武藤 裕

Summary The pre-spliceosomal complex involves interactions between U1 and U2 snRNPs, where a ubiquitin-like domain (ULD) of SF3A1, a component of U2 snRNP, binds to the stem-loop 4 (SL4; the UUCG tetraloop) of U1 snRNA in U1 snRNP. Here, we reported the 1.80 Å crystal structure of human SF3A1 ULD (ULDSF3A1) complexed with SL4. The structural part of ULDSF3A1 (res. 704–785) adopts a typical β-grasp fold with a topology of β1-β2-α1-310a-β3-β4-310b-β5, closely resembling that of ubiquitin, except for the length and structure of the β1/β2 loop. A patch on the surface formed by three ULDSF3A1-specific residues, Lys756 (β3), Phe763 (β4), and Lys765 (following β4), contacts the canonical UUCG tetraloop structure. In contrast, the directly following C-terminal tail composed of 786KERGGRKK793 was essentially stretched. The main or side chains of all the residues interacted with the major groove of the stem helix; the RGG residues adopted a peculiar conformation for RNA recognition. These findings were confirmed by mutational studies using bio-layer interferometry. Collectively, a unique combination of the β-grasp fold and the C-terminal tail constituting ULDSF3A1 is required for the SL4-specific binding. This interaction mode also suggests that putative post-translational modifications, including ubiquitination in ULDSF3A1, directly inhibit SL4 binding.

In humans, YTH (YT521-B homology) domain containing protein 2 (YTHDC2) plays a crucial role in the phase-shift from mitosis to meiosis. YTH domains bind to methylated adenosine nucleotides such as m6A. In a phylogenic tree, the YTH domain of YTHDC2 (YTH2) and that of the YTH containing protein YTHDC1 (YTH1) belong to the same sub-group. However, the binding affinity of m6A differs between these proteins. Here, we report 1H, 13C and 15N resonance assignment of YTH2 and its solution structure to examine the difference of the structural architecture and the dynamic properties of YTH1 and YTH2. YTH2 adopts a β1-α1-β2-α2-β3-β4-β5-α3-β6-α4 topology, which was also observed in YTH1. However, the β4-β5 loops of YTH1 and YTH2 are distinct in length and amino acid composition. Our data revealed that, unlike in YTH1, the structure of m6A-binding pocket of YTH2 formed by the β4-β5 loop is stabilized by electrostatic interaction. This assignment and the structural information for YTH2 will provide the insight on the further functional research of YTHDC2.

The accurate exclusion of introns by RNA splicing is critical for the production of mature mRNA. U2AF1 binds specifically to the 3´ splice site, which includes an essential AG dinucleotide. Even a single amino acid mutation of U2AF1 can cause serious disease such as certain cancers or myelodysplastic syndromes. Here, we describe the first crystal structures of wild-type and pathogenic mutant U2AF1 complexed with target RNA, revealing the mechanism of 3´ splice site selection, and how aberrant splicing results from clinically important mutations. Unexpected features of this mechanism may assist the future development of new treatments against diseases caused by splicing errors.

The spliceosomal protein SF3b49, a component of the splicing factor 3b (SF3b) protein complex in the U2 small nuclear ribonucleoprotein, contains two RNA recognition motif (RRM) domains. In yeast, the first RRM domain (RRM1) of Hsh49 protein (yeast orthologue of human SF3b49) reportedly interacts with another component, Cus1 protein (orthologue of human SF3b145). Here, we solved the solution structure of the RRM1 of human SF3b49 and examined its mode of interaction with a fragment of human SF3b145 using NMR methods. Chemical shift mapping showed that the SF3b145 fragment spanning residues 598-631 interacts with SF3b49 RRM1, which adopts a canonical RRM fold with a topology of 1-1-2-3-2-4. Furthermore, a docking model based on NOESY measurements suggests that residues 607-616 of the SF3b145 fragment adopt a helical structure that binds to RRM1 predominantly via 1, consequently exhibiting a helix-helix interaction in almost antiparallel. This mode of interaction was confirmed by a mutational analysis using GST pull-down assays. Comparison with structures of all RRM domains when complexed with a peptide found that this helix-helix interaction is unique to SF3b49 RRM1. Additionally, all amino acid residues involved in the interaction are well conserved among eukaryotes, suggesting evolutionary conservation of this interaction mode between SF3b49 RRM1 and SF3b145. PDB Code(s):

p54(nrb)/NonO is a nuclear RNA-binding protein involved in many cellular events such as pre-mRNA processing, transcription, and nuclear retention of hyper-edited RNAs. In particular, it participates in the splicing process by directly binding the 5' splice site of pre-mRNAs. The protein also concentrates in a nuclear body called paraspeckle by binding a G-rich segment of the ncRNA NEAT1. The N-termirial section of p54(nrb)/NonO contains tandem RNA recognition motifs (RRMs) preceded by an HQ-rich region including a threonine residue (Thr15) whose,phosphorylation inhibits its RNA binding ability, except for G-rich RNAs. In this work, our goal was to understand the rules that characterize the binding of the p54(nrb)/NonO RRMs to their RNA target. We have done in vitro RNA binding experiments which revealed that only the first RRM of p54(nrb)/NonO binds to the 5' splice site RNA We have then determined the structure of the p54(nrb)/NonO RRM1 by liquid-state NMR which revealed the presence of a canonical fold (beta 1 alpha 1 beta 2 beta 3 alpha 2 beta 4) and the conservation of aromatic amino acids at the protein surface. We also investigated the dynamics of this domain by NMR. The p54(nrb)/NonO RRM1 displays some motional properties that are typical of a well-folded protein with some regions exhibiting more flexibility (loops and beta-strands). Furthermore, we determined the affinity of p54(nrb)/NonO RRM1 interaction to the 5' splice site RNA by NMR and fluorescence quenching and mapped its binding interface by NMR, concluding in a classical nucleic acid interaction. This study provides an improved understanding of the molecular basis (structure and dynamics) that governs the binding of the p54(nrb)/NonO RRM1 to one of its target RNAs.

The pre-mRNA splicing reaction of eukaryotic cells has to be carried out extremely accurately, as failure to recognize the splice sites correctly causes serious disease. The small subunit of the U2AF heterodimer is essential for the determination of 3 ' splice sites in pre-mRNA splicing, and several single-residue mutations of the U2AF small subunit cause severe disorders such as myelodysplastic syndromes. However, the mechanism of RNA recognition is poorly understood. Here we solved the crystal structure of the U2AF small subunit (U2AF23) from fission yeast, consisting of an RNA recognition motif (RRM) domain flanked by two conserved CCCH-type zinc fingers (ZFs). The two ZFs are positioned side by side on the beta sheet of the RRM domain. Further mutational analysis revealed that the ZFs bind cooperatively to the target RNA sequence, but the RRM domain acts simply as a scaffold to organize the ZFs and does not itself contact the RNA directly. This completely novel and unexpected mode of RNA-binding mechanism by the U2AF small subunit sheds light on splicing errors caused by mutations of this highly conserved protein.

D-Serine is an essential coagonist with glutamate for stimulation of N-methyl-D-aspartate (NMDA) glutamate receptors. Although astrocytic metabolic processes are known to regulate synaptic glutamate levels, mechanisms that control D-serine levels are not well defined. Here we show that D-serine production in astrocytes is modulated by the interaction between the D-serine synthetic enzyme serine racemase (SRR) and a glycolytic enzyme, glyceraldehyde 3-phosphate dehydrogenase (GAPDH). In primary cultured astrocytes, glycolysis activity was negatively correlated with D-serine level. We show that SRR interacts directly with GAPDH, and that activation of glycolysis augments this interaction. Biochemical assays using mutant forms of GAPDH with either reduced activity or reduced affinity to SRR revealed that GAPDH suppresses SRR activity by direct binding to GAPDH and through NADH, a product of GAPDH. NADH allosterically inhibits the activity of SRR by promoting the disassociation of ATP from SRR. Thus, astrocytic production of D-serine is modulated by glycolytic activity via interactions between GAPDH and SRR. We found that SRR is expressed in astrocytes in the subiculum of the human hippocampus, where neurons are known to be particularly vulnerable to loss of energy. Collectively, our findings suggest that astrocytic energy metabolism controls D-serine production, thereby influencing glutamatergic neurotransmission in the hippocampus.

We developed fluorescent turn-on probes containing a fluorescent nucleoside, 5-(benzofuran-2-yl) deoxyuridine (dU(BF)) or 5-(3-methylbenzofuran-2-yl) deoxyuridine (dU(MBF)), for the detection of single-stranded DNA or RNA by utilizing DNA triplex formation. Fluorescence measurements revealed that the probe containing dUMBF achieved superior fluorescence enhancement than that containing dU(BF). NMR and fluorescence analyses indicated that the fluorescence intensity increased upon triplex formation partly as a consequence of a conformational change at the bond between the 3-methylbenzofuran and uracil rings. In addition, it is suggested that the microenvironment around the 3-methylbenzofuran ring contributed to the fluorescence enhancement. Further, we developed a method for detecting RNA by rolling circular amplification in combination with triplex-induced fluorescence enhancement of the oligonucleotide probe containing dU(MBF).

The family of cytoplasmic polyadenylation element binding proteins CPEB1, CPEB2, CPEB3, and CPEB4 binds to the 3'-untranslated region (3'-UTR) of mRNA, and plays significant roles in mRNA metabolism and translation regulation. They have a common domain organization, involving two consecutive RNA recognition motif (RRM) domains followed by a zinc finger domain in the C-terminal region. We solved the solution structure of the first RRM domain (RRM1) of human CPEB3, which revealed that CPEB3 RRM1 exhibits structural features distinct from those of the canonical RRM domain. Our structural data provide important information about the RNA binding ability of CPEB3 RRM1. (C) 2014 Wiley Periodicals, Inc.

Tissue-specific alternative pre-mRNA splicing is often cooperatively regulated by multiple splicing factors, but the structural basis of cooperative RNA recognition is poorly understood. In Caenorhabditis elegans, ligand binding specificity of fibroblast growth factor receptors (FGFRs) is determined by mutually exclusive alternative splicing of the sole FGFR gene, egl-15. Here we determined the solution structure of a ternary complex of the RNA-recognition motif (RRM) domains from the RBFOX protein ASD-1, SUP-12 and their target RNA from egl-15. The two RRM domains cooperatively interact with the RNA by sandwiching a G base to form the stable complex. Multichromatic fluorescence splicing reporters confirmed the requirement of the G and the juxtaposition of the respective cis elements for effective splicing regulation in vivo. Moreover, we identified a new target for the heterologous complex through an element search, confirming the functional significance of the intermolecular coordination.

Tissue-specific alternative pre-mRNA splicing is often cooperatively regulated by multiple splicing factors, but the structural basis of cooperative RNA recognition is poorly understood. In Caenorhabditis elegans, ligand binding specificity of fibroblast growth factor receptors (FGFRs) is determined by mutually exclusive alternative splicing of the sole FGFR gene, egl-15. Here we determined the solution structure of a ternary complex of the RNA-recognition motif (RRM) domains from the RBFOX protein ASD-1, SUP-12 and their target RNA from egl-15. The two RRM domains cooperatively interact with the RNA by sandwiching a G base to form the stable complex. Multichromatic fluorescence splicing reporters confirmed the requirement of the G and the juxtaposition of the respective cis elements for effective splicing regulation in vivo. Moreover, we identified a new target for the heterologous complex through an element search, confirming the functional significance of the intermolecular coordination.

Anaphase-promoting complex or cyclosome (APC/C) is a multisubunit ubiquitin ligase E3 that targets cell-cycle regulators. Cdc20 is required for full activation of APC/C in M phase, and mediates substrate recognition. In vertebrates, Emi2/Erp1/FBXO43 inhibits APC/C-Cdc20, and functions as a cytostatic factor that causes long-term M phase arrest of mature oocytes. In this study, we found that a fragment corresponding to the zinc-binding region (ZBR) domain of Emi2 inhibits cell-cycle progression, and impairs the association of Cdc20 with the APC/C core complex in HEK293T cells. Furthermore, we revealed that the ZBR fragment of Emi2 inhibits in vitro ubiquitin chain elongation catalyzed by the APC/C cullin-RING ligase module, the ANAPC2-ANAPC11 subcomplex, in combination with the ubiquitin chain-initiating E2, E2C/UBE2C/UbcH10. Structural analyses revealed that the Emi2 ZBR domain uses different faces for the two mechanisms. Thus, the double-faced ZBR domain of Emi2 antagonizes the APC/C function by inhibiting both the binding with the coactivator Cdc20 and ubiquitylation mediated by the cullin-RING ligase module and E2C. In addition, the tail region between the ZBR domain and the C-terminal RL residues [the post-ZBR (PZ) region] interacts with the cullin subunit, ANAPC2. In the case of the ZBR fragment of the somatic paralogue of Emi2, Emi1/FBXO5, these inhibitory activities against cell division and ubiquitylation were not observed. Finally, we identified two sets of key residues in the Emi2 ZBR domain that selectively exert each of the dual Emi2-specific modes of APC/C inhibition, by their mutation in the Emi2 ZBR domain and their transplantation into the Emi1 ZBR domain. (C) 2014 The Authors. Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies. This is an open access article under the CC BY-NC-ND license

Aggregation of TAR DNA-binding protein of 43 kDa (TDP-43) is a pathological signature of amyotrophic lateral sclerosis (ALS). Although accumulating evidence suggests the involvement of RNA recognition motifs (RRMs) in TDP-43 proteinopathy, it remains unclear how native TDP-43 is converted to pathogenic forms. To elucidate the role of homeostasis of RRM1 structure in ALS pathogenesis, conformations of RRM1 under high pressure were monitored by NMR. We first found that RRM1 was prone to aggregation and had three regions showing stable chemical shifts during misfolding. Moreover, mass spectrometric analysis of aggregated RRM1 revealed that one of the regions was located on protease-resistant beta-strands containing two cysteines (Cys-173 and Cys-175), indicating that this region served as a core assembly interface in RRM1 aggregation. Although a fraction of RRM1 aggregates comprised disulfide-bonded oligomers, the substitution of cysteine(s) to serine(s) (C/S) resulted in unexpected acceleration of amyloid fibrils of RRM1 and disulfide-independent aggregate formation of full-length TDP-43. Notably, TDP-43 aggregates with RRM1-C/S required the C terminus, and replicated cytopathologies of ALS, including mislocalization, impaired RNA splicing, ubiquitination, phosphorylation, and motor neuron toxicity. Furthermore, RRM1-C/S accentuated inclusions of familial ALS-linked TDP-43 mutants in the C terminus. The relevance of RRM1-C/S-induced TDP-43 aggregates in ALS pathogenesis was verified by immunolabeling of inclusions of ALS patients and cultured cells overexpressing the RRM1-C/S TDP-43 with antibody targeting misfolding-relevant regions. Our results indicate that cysteines in RRM1 crucially govern the conformation of TDP-43, and aberrant self-assembly of RRM1 at amyloidogenic regions contributes to pathogenic conversion of TDP-43 in ALS.

RNA helicase A (RHA) is a multifunctional protein that regulates gene expression. RHA has two double-stranded RNA-binding domains (dsRBDs) that serve as modules for highly structured RNA binding and protein-protein interactions. Using the dsRBDs, RHA binds to cellular and viral mRNAs, exports them from the nucleus, and regulates splicing as well as translational initiation. The RHA dsRBDs also reportedly mediate interactions with small RNAs and other dsRBD-containing proteins, and altogether form a processing complex involved in RNA silencing pathways. In addition, the RHA dsRBDs bridge RNA polymerase II with several transcription factors. Here we report the 1H, 13C, and 15N chemical shift assignments of the dsRBDs of RHA. The resonance assignments obtained in this work will contribute to the elucidation of the interactions between RHA and transcriptional or post-transcriptional gene regulators. © 2012 Springer Science+Business Media B.V.

Background: Interactions between p53 and Bcl-2 family proteins serve a critical role in transcription-independent p53 apoptosis. Results: We studied the interactions of p53TAD2 with anti-apoptotic Bcl-2 family proteins at the atomic level by NMR, mutagenesis, and structure calculation. Conclusion: Bcl-XL/Bcl-2, MDM2, and CBP/p300 share similar modes of binding to the dual p53TAD motifs. Significance: Dual-site interaction of p53TAD is a highly conserved mechanism in the transcription-dependent and transcription- independent p53 apoptotic pathways. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.

The WWE domain is often identified in proteins associated with ubiquitination or poly-ADP-ribosylation. Structural information about WWE domains has been obtained for the ubiquitination-related proteins, such as Deltex and RNF146, but not yet for the poly-ADP-ribose polymerases (PARPs). Here we determined the solution structures of the WWE domains from PARP11 and PARP14, and compared them with that of the RNF146 WWE domain. NMR perturbation experiments revealed the specific differences in their ADP-ribose recognition modes that correlated with their individual biological activities. The present structural information sheds light on the ADP-ribose recognition modes by the PARP WWE domains. (C) 2012 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.

RNA helicase A (RHA) is a highly conserved protein with multifaceted functions in the gene expression of cellular and viral mRNAs. RHA recognizes highly structured nucleotides and catalytically rearranges the various interactions between RNA, DNA, and protein molecules to provide a platform for the ribonucleoprotein complex. We present the first solution structures of the double-stranded RNA-binding domains (dsRBDs), dsRBD1 and dsRBD2, from mouse RHA. We discuss the binding mode of the dsRBDs of RHA, in comparison with the known dsRBD structures in their complexes. Our structural data provide important information for the elucidation of the molecular reassembly mediated by RHA. Proteins 2012;. (c) 2012 Wiley Periodicals, Inc.

Multi-targeting therapy is an emerging strategy of drug discovery to improve therapeutic efficacy, safety and resistance profiles. In this study, we monitored the binding of a potent MDM2 inhibitor Nutlin-3 with anti-apoptotic Bcl-2 family proteins using NMR spectroscopy. Our results showed the universal binding of Nutlin-3 with diverse anti-apoptotic Bcl-2 family proteins. Taken together with the binding data for Nutlin-3 analogs, the structural model of the Bcl-X-L/Nutlin-3 complex showed that the binding mode of Nutlin-3 resembles that of the Bcl-X-L/Bcl-2 inhibitors, suggesting the molecular mechanism of transcription-independent mitochondrial apoptosis by Nutlin-3. Finally, our structural comparison provides structural insights into the dual-targeting mechanism of how Nutlin-3 can bind to two different target proteins, MDM2 and anti-apoptotic Bcl-2 family proteins in a similar manner. (C) 2012 Elsevier Inc. All rights reserved.

'RNA recognition motifs (RRMs)' are common domain-folds composed of 80-90 amino-acid residues in eukaryotes, and have been identified in many cellular proteins. At first they were known as RNA binding domains. Through discoveries over the past 20 years, however, the RRMs have been shown to exhibit versatile molecular recognition activities and to behave as molecular Lego building blocks to construct biological systems. Novel RNA/protein recognition modes by RRMs are being identified, and more information about the molecular recognition by RRMs is becoming available. These RNA/protein recognition modes are strongly correlated with their biological significance. In this review, we would like to survey the recent progress on these versatile molecular recognition modules. (C) 2012 John Wiley & Sons, Ltd.

Human Transformer2-beta (hTra2-beta) is an important member of the serine/arginine-rich protein family, and contains one RNA recognition motif (RRM). It controls the alternative splicing of several pre-mRNAs, including those of the calcitonin/calcitonin gene-related peptide (CGRP), the survival motor neuron 1 (SMN1) protein and the tau protein. Accordingly, the RRM of hTra2-beta specifically binds to two types of RNA sequences [the CAA and (GAA)(2) sequences]. We determined the solution structure of the hTra2-beta RRM (spanning residues Asn110-Thr201), which not only has a canonical RRM fold, but also an unusual alignment of the aromatic amino acids on the beta-sheet surface. We then solved the complex structure of the hTra2-beta RRM with the (GAA)(2) sequence, and found that the AGAA tetra-nucleotide was specifically recognized through hydrogen-bond formation with several amino acids on the N- and C-terminal extensions, as well as stacking interactions mediated by the unusually aligned aromatic rings on the beta-sheet surface. Further NMR experiments revealed that the hTra2-beta RRM recognizes the CAA sequence when it is integrated in the stem-loop structure. This study indicates that the hTra2-beta RRM recognizes two types of RNA sequences in different RNA binding modes.

The TAR RNA-binding Protein (TRBP) is a double-stranded RNA (dsRNA)-binding protein, which binds to Dicer and is required for the RNA interference pathway. TRBP consists of three dsRNA-binding domains (dsRBDs). The first and second dsRBDs (dsRBD1 and dsRBD2, respectively) have affinities for dsRNA, whereas the third dsRBD (dsRBD3) binds to Dicer. In this study, we prepared the single domain fragments of human TRBP corresponding to dsRBD1 and dsRBD2 and solved the crystal structure of dsRBD1 and the solution structure of dsRBD2. The two structures contain an alpha-beta-beta-beta-alpha fold, which is common to the dsRBDs. The overall structures of dsRBD1 and dsRBD2 are similar to each other, except for a slight shift of the first alpha helix. The residues involved in dsRNA binding are conserved. We examined the small interfering RNA (siRNA)-binding properties of these dsRBDs by isothermal titration colorimetry measurements. The dsRBD1 and dsRBD2 fragments both bound to siRNA, with dissociation constants of 220 and 113 nM, respectively. In contrast, the full-length TRBP and its fragment with dsRBD1 and dsRBD2 exhibited much smaller dissociation constants (0.24 and 0.25 nM, respectively), indicating that the tandem dsRBDs bind simultaneously to one siRNA molecule. On the other hand, the loop between the first alpha helix and the first beta strand of dsRBD2, but not dsRBD1, has a Trp residue, which forms hydrophobic and cation-pi interactions with the surrounding residues. A circular dichroism analysis revealed that the thermal stability of dsRBD2 is higher than that of dsRBD1 and depends on the Trp residue.

The zinc finger CW (zf-CW) domain is a motif of about 60 residues that is frequently found in proteins involved in epigenetic regulation. Here, we determined the NMR solution structure of the zf-CW domain of the human zf-CW and PWWP domain containing protein 1 (ZCWPW1). The zf-CW domain adopts a new fold in which a zinc ion is coordinated tetrahedrally by four conserved Cys ligand residues. The tertiary structure of the zf-CW domain partially resembles that adopted by the plant homeo domain (PHD) finger bound to the histone tail, suggesting that the zf-CW domain and the PHD finger have similar functions. The solution structure of the complex of the zf-CW domain with the histone H3 tail peptide (1-10) with trimethylated K4 clarified its binding mode. Our structural and biochemical studies have identified the zf-CW domain as a member of the histone modification reader modules for epigenetic regulation.

The Notch signaling pathway is critical for many developmental processes and requires complex trafficking of both Notch receptor and its ligands, Delta and Serrate. In Drosophila melanogaster, the endocytosis of Delta in the signal-sending cell is essential for Notch receptor activation. The Neuralized protein from D. melanogaster (Neur) is a ubiquitin E3 ligase, which binds to Delta through its first neuralized homology repeat 1 (NHR1) domain and mediates the ubiquitination of Delta for endocytosis. Tom, a Bearded protein family member, inhibits the Neur-mediated endocytosis through interactions with the NHR1 domain. We have identified the domain boundaries of the novel NHR1 domain, using a screening system based on our cell-free protein synthesis method, and demonstrated that the identified Neur NHR1 domain had binding activity to the 20-residue peptide corresponding to motif 2 of Tom by isothermal titration calorimetry experiments. We also determined the solution structure of the Neur NHR1 domain by heteronuclear NMR methods, using a (15)N/(13)C-labeled sample. The Neur NHR1 domain adopts a characteristic beta-sandwich fold, consisting of a concave five-stranded antiparallel beta-sheet and a convex seven-stranded antiparallel beta-sheet. The long loop (L6) between the beta 6 and beta 7 strands covers the hydrophobic patch on the concave beta-sheet surface, and the Neur NHR1 domain forms a compact globular fold. Intriguingly, in spite of the slight, but distinct, differences in the topology of the secondary structure elements, the structure of the Neur NHR1 domain is quite similar to those of the B30.2/SPRY domains, which are known to mediate specific protein-protein interactions. Further NMR titration experiments of the Neur NHR1 domain with the 20-residue Tom peptide revealed that the resonances originating from the bottom area of the beta-sandwich (the L3, L5, and L11 loops, as well as the tip of the L6 loop) were affected. In addition, a structural comparison of the Neur NHR1 domain with the first NMR domain of the human KIAA1787 protein, which is from another NHR subfamily and does not bind to the 20-residue Tom peptide, suggested the critical amino acid residues for the interactions between the Neur NHR1 domain and the Tom peptide. The present structural study will shed light on the role of the Neur NHR1 domain in the Notch signaling pathway. (C) 2009 Elsevier Ltd. All rights reserved.

Most human protein-encoding genes contain multiple exons that are spliced together, frequently in alternative arrangements, by the spliceosome. It is established that U1 snRNP is an essential component of the spliceosome, in human consisting of RNA and ten proteins, several of which are post-translationally modified and exist as multiple isoforms. Unresolved and challenging to investigate are the effects of these post translational modifications on the dynamics, interactions and stability of the particle. Using mass spectrometry we investigate the composition and dynamics of the native human U1 snRNP and compare native and recombinant complexes to isolate the effects of various subunits and isoforms on the overall stability. Our data reveal differential incorporation of four protein isoforms and dynamic interactions of subunits U1-A, U1-C and Sm-B/B'. Results also show that unstructured post-translationally modified C-terminal tails are responsible for the dynamics of Sm-B/B' and U1-C and that their interactions with the Sm core are controlled by binding to different U1-70k isoforms and their phosphorylation status in vivo. These results therefore provide the important functional link between proteomics and structure as well as insight into the dynamic quaternary structure of the native U1 snRNP important for its function.

The CUG-binding protein 1 (CUG-BP1) is a member of the CUG-BP1 and ETR-like factors (CELF) family or the Bruno-like family and is involved in the control of splicing, translation and mRNA degradation. Several target RNA sequences of CUG-BP1 have been predicted, such as the CUG triplet repeat, the GU-rich sequences and the AU-rich element of nuclear pre-mRNAs and/or cytoplasmic mRNA. CUG-BP1 has three RNA-recognition motifs (RRMs), among which the third RRM (RRM3) can bind to the target RNAs on its own. In this study, we solved the solution structure of the CUG-BP1 RRM3 by hetero-nuclear NMR spectroscopy. The CUG-BP1 RRM3 exhibited a noncanonical RRM fold, with the four-stranded beta-sheet surface tightly associated with the N-terminal extension. Furthermore, we determined the solution structure of the CUG-BP1 RRM3 in the complex with (UG)(3) RNA, and discovered that the UGU trinucleotide is specifically recognized through extensive stacking interactions and hydrogen bonds within the pocket formed by the beta-sheet surface and the N-terminal extension. This study revealed the unique mechanism that enables the CUG-BP1 RRM3 to discriminate the short RNA segment from other sequences, thus providing the molecular basis for the comprehension of the role of the RRM3s in the CELF/Bruno-like family.

The human AU RNA binding protein/enoyl-Coenzyme A hydratase (AUH) is a 3-hydroxy-3-methylglutaconyl-CoA dehydratase in the leucine degradation pathway. It also possesses an RNA-binding activity to AUUU repeats, which involves no known conserved RNA-binding domains and is seemingly unrelated to the enzymatic activity. In this study, we performed mass spectrometric analyses to elucidate the oligomeric states of AUH in the presence and absence of RNA. With a short RNA (AUUU) or without RNA, AUH mainly exists as a trimer in solution. On the other hand, the AUH trimer dimerizes upon binding to one molecule of a long RNA containing 24 repeats of the AUUU motif, (AUUU)(24)A. AUH was crystallized with the long RNA. Although the RNA was disordered in the crystalline lattice, the AUH structure was determined as an asymmetric dimer of trimers with a kink in the alignment of the trimer axes, resulting in the formation of two clefts with significantly different sizes.

Fn14 is the smallest member of the tumor necrosis factor (TNF) receptor superfamily, and specifically binds to its ligand, TWEAK (TNF-like weak inducer of apoptosis), which is a member of the TNF superfamily. The receptor-ligand recognition between Fn14 and TWEAK induces a variety of cellular processes for tissue remodeling and is also involved in the pathogenesis of some human diseases, such as cancer, chronic autoimmune diseases, and acute ischaemic stroke. The extracellular ligand-binding region of Fn14 is composed of 53 amino acid residues and forms a single, cysteine-rich domain (CRD). In this study, we determined the solution structure of the Fn14 CRD (Glu28-Ala70) by heteronuclear NMR, with a (13)C-/(15)N-labeled sample. The tertiary structure of the CRD comprises a beta-sheet with two strands, followed by a 3(10) helix and a C-terminal alpha-helix, and is stabilized by three disulfide bonds connecting Cys36-Cys49, Cys52-Cys67, and Cys55-Cys64. Comparison of the disulfide bond connectivities and the tertiary structures with those of other CRDs revealed that the Fn14 CRD is similar to the fourth CRD of TNF receptor 1 (A1-C2 module type), but not to the CRD of B-cell maturation antigen and the second CRD of transmembrane activator and CAML (calcium modulator and cyclophilin ligand) interactor (A1-D2 module type). This is the first structural report about the A1-C2 type CRD that could bind to the known target.

The muscleblind-like (MBNL) proteins 1, 2, and 3, which contain four CCCH zinc finger motifs (ZF1-4), are involved in the differentiation of muscle inclusion by controlling the splicing patterns of several pre-mRNAs. Especially, MBNL1 plays a crucial role in myotonic dystrophy. The CCCH zinc finger is a sequence motif found in many RNA binding proteins and is suggested to play an important role in the recognition of RNA molecules. Here, we solved the solution structures of both tandem zinc finger (TZF) motifs, TZF12 (comprising ZF1 and ZF2) and TZF34 (ZF3 and ZF4), in MBNL2 from Homo sapiens. In TZF12 of MBNL2, ZF1 and ZF2 adopt a similar fold, as reported previously for the CCCH-type zinc fingers in the TIS11d protein. The linker between ZF1 and ZF2 in MBNL2 forms an antiparallel beta-sheet with the N-terminal extension of ZF1. Furthermore, ZF1 and ZF2 in MBNL2 interact with each other through hydrophobic interactions. Consequently, TZF12 forms a single, compact global fold, where ZF1 and ZF2 are approximately symmetrical about the C2 axis. The structure of the second tandem zinc finger (TZF34) in MBNL2 is similar to that of TZF12. This novel three-dimensional structure of the TZF domains in MBNL2 provides a basis for functional studies of the CCCH-type zinc finger motifs in the MBNL protein family.

Methylation of the NI atom of guanosine at position 37 in tRNA, the position 3(1)-adjacent to the anticodon, generates the modified nucleoside m(1)G37. In archaea and eukaryotes, m(1)G37 synthesis is catalyzed by tRNA(m(1)G37)methyltransferase (archaeal or eukaryotic Trm5, a/eTrm5). Here we report the crystal structure of archaeal Trm5 (aTrm5) from Methanocaldococcus jannaschii (formerly known as Methanococcus jannaschii) in complex with the methyl donor analogue at 2.2 angstrom resolution. The crystal structure revealed that the entire protein is composed of three structural domains, D1, D2, and D3. In the a/eTrm5 primary structures, D2 and D3 are highly conserved, while D1 is not conserved. The D3 structure is the Rossmann fold, which is the hallmark of the canonical class-I methyltransferases. The a/eTrm5-defining domain, D2, exhibits structural similarity to some class-I methyltransferases. In contrast, a DAM search with the DI structure yielded no structural homologues. In the crystal structure, D3 contacts both DI and D2. The residues involved in the DI:D3 interactions are not conserved, while those participating in the D2:D3 interactions are well conserved. DI and D2 do not contact each other, and the linker between them is disordered. aTrm5 fragments corresponding to the DI and D2-D3 regions were prepared in a soluble form. The NMR analysis of the DI fragment revealed that DI is well folded by itself, and it did not interact with either the D2-D3 fragment or the tRNA. The NMR analysis of the D2-D3 fragment revealed that it is well folded, independently of DI, and that it interacts with tRNA. Furthermore, the D2-D3 fragment was as active as the full-length enzyme for tRNA methylation. The positive charges on the surface of D2-D3 may be involved in tRNA binding. Therefore, these findings suggest that the interaction between DI and D3 is not persistent, and that the D2-D3 region plays the major role in tRNA methylation.

The degradation of the poly(A) tail is crucial for posttranscriptional gene regulation and for quality control of mRNA. Poly(A)-specific ribonuclease (PARN) is one of the major mammalian 3 specific exo-ribonucleases involved in the degradation of the mRNA poly(A) tail, and it is also involved in the regulation of translation in early embryonic development. The interaction between PARN and the m(7)GpppG cap of mRNA plays a key role in stimulating the rate of deadenylation. Here we report the solution structures of the cap-binding domain of mouse PARN with and without the m(7)GpppG cap analog. The structure of the cap-binding domain adopts the RNA recognition motif (RRM) with a characteristic -helical extension at its C-terminus, which covers the -sheet surface (hereafter referred to as PARN RRM). In the complex structure of PARN RRM with the cap analog, the base of the N(7)-methyl guanosine (m(7)G) of the cap analog stacks with the solvent-exposed aromatic side chain of the distinctive tryptophan residue 468, located at the C-terminal end of the second -strand. These unique structural features in PARN RRM reveal a novel cap-binding mode, which is distinct from the nucleotide recognition mode of the canonical RRM domains.

T cell intracellular antigen-1 (TIA-1), an apoptosis promoting factor, functions as a splicing regulator for the Fas pre-mRNA. TIA-1 possesses three RNA recognition motifs (RRMs) and a glutamine-rich domain. The second RRM (RRM2) is necessary and sufficient for tight, sequence-specific binding to the uridine-rich sequences buried around the 5' splice sites. In the present study, we solved the solution structure of the murine TIA-1 RRM2 by heteronuclear-nuclear magnetic resonance spectroscopy. The TIA-1 RRM2 adopts the RRM fold (beta alpha beta beta alpha beta) and possesses an extra beta-strand between beta 2 and beta 3, which forms an additional beta-sheet with the C-terminal part of beta 2. We refer to this structure as the beta 2-beta 2' beta-loop. Interestingly, this characteristic beta-loop structure is conserved among a number of RRMs, including the U2AF65 RRM2 and the Sex-lethal RRM1 and RRM2, which also bind to uridine-rich RNAs. Furthermore, we identified a new sequence motif in the beta 2-beta 2' beta-loop, the DxxT motif. Chemical shift perturbation analyses of both the main and side chains upon binding to the uridine pentamer RNA revealed that most of the beta-sheet surface, including the beta 2-beta 2' beta-loop, is involved in the RNA binding. An investigation of the chemical shift perturbation revealed similarity in the RNA recognition modes between the TIA-1 and U2AF65 RRMs.

The spliceosomal protein p14, a component of the SF3b complex in the U2 small nuclear ribonucleoprotein.(snRNP), is essential for the U2 snRNP to recognize the branch site adenosine. The elucidation of the dynamic process of the splicing machinery rearrangement awaited the solution structural information. We identified a suitable complex of human p14 and the SF3b155 fragment for the determination of its solution structure by NMR. In addition to the overall structure Of the complex, which was recently reported in a crystallographic study (typical RNA recognition motif fold beta 1-alpha 1-beta 2-beta 3-alpha 2-beta 4 of p14, and alpha A-beta A fold of the SF3b155 fragment), we identified three important features revealed by the NMR solution structure. First, the C-terminal extension and. the nuclear localization signal of p14 (alpha 3 and alpha 4 in the crystal structure, respectively) were dispensable for the complex formation. Second, the proline-rich segment of SF3b155, following beta A, closely approaches p14. Third, interestingly, the beta 1-alpha 1 loop and the alpha 2-beta 4 beta-hairpin form a positively charged groove. Extensive mutagenesis analyses revealed the functional relevance of the residues involved in the protein-protein interactions: two aromatic residues of SF3b155 (Phe408 and Tyr412) play crucial roles in the complex formation, and two hydrophobic residues (Val414 and Leu415) in SF3b 155 serve as an anchor for the complex formation, by cooperating with the aromatic residues. These findings clearly led to the conclusion that SFb155 binds to p14 with three contact points, involving Phe408, Tyr412, and Val414/Leu415. Furthermore, to dissect the interactions between p 14 and the branch site RNA, we performed chemical-shift-perturbation experiments, not only for the main-chain but also for the side-chain resonances, for several p14-SF3b155 complex constructs upon binding to RNA. These analyses identified a positively charged groove and the C-terminal extension of p14 as RNA-binding sites. Strikingly, an aromatic residue in the beta 1-alpha 1 loop, Tyr28, and a positively charged residue in the alpha 2-beta 4 beta-hairpin, Agr85, are critical for the RNA-binding activity of the positively charged groove. The 7yr28Ala and Arg85Ala point mutants and a deletion mutant of the C-terminal extension clearly revealed that their RNA binding activities were independent of each other. Collectively, this study provides details for the protein-recognition mode of p14 and insight into the branch site recognition.

The RimM protein has been implicated in the maturation of the 30S ribosomal subunit. It binds to ribosomal protein S19, located in the head domain of the 30S subunit. Multiple sequence alignments predicted that RimM possesses two domains in its N- and C-terminal regions. In the present study, we have produced Thermus thermophilus RimM in both the full-length form (162 residues) and its N-terminal fragment, spanning residues I to 85, as soluble proteins in Escherichia coli and have performed structural analyses by nuclear magnetic resonance spectroscopy. Residues I to 80 of the RimM protein fold into a single structural domain adopting a six-stranded P-barrel fold. On the other hand, the C-terminal region of RimM (residues 81 to 162) is partly folded in solution. Analyses of H-1-N-15 heteronuclear single quantum correlation spectra revealed that a wide range of residues in the C-terminal region, as well as the residues in the vicinity of a hydrophobic patch in the N-terminal domain, were dramatically affected upon complex formation with ribosomal protein S19.

The zinc finger HIT domain is a sequence motif found in many proteins, including thyroid hormone receptor interacting protein 3 (TRIP-3), which is possibly involved in maturity-onset diabetes of the young (MODY). Novel zinc finger motifs are suggested to play important roles in gene regulation and chromatin remodeling. Here, we determined the high-resolution solution structure of the zinc finger HIT domain in ZNHIT2 (protein FON) from Homo sapiens, by an NMR method based on 567 upper distance limits derived from NOE intensities measured in three-dimensional NOESY spectra. The structure yielded a backbone RMSD to the mean coordinates of 0.19 angstrom for the structured residues 12-48. The fold consists of two consecutive antiparallel beta-sheets and two short C-terminal helices packed against the second beta-sheet, and binds two zinc ions. Both zinc ions are coordinated tetrahedrally via a CCCC-CCHC motif to the ligand residues of the zf-HIT domain in an interleaved manner. The tertiary structure of the zinc finger HIT domain closely resembles the folds of the B-box, RING finger, and PHD domains with a cross-brace zinc coordination mode, but is distinct from them. The unique three-dimensional structure of the zinc finger HIT domain revealed a novel zinc-binding fold, as a new member of the treble clef domain family. On the basis of the structural data, we discuss the possible functional roles of the zinc finger HIT domain.

The SF3a complex, consisting of SF3a60, SF3a66, and SF3a120, in 17S U2 snRNP is crucial to spliceosomal assembly. SF3a120 contains two tandem SURP domains (SURP1 and SURP2), and SURP2 is responsible for binding to SF3a60. We found that the SURP2 fragment forms a stable complex with an SF3a60 fragment (residues 71-107) and solved its structure by NMR spectroscopy. SURP2 exhibits a fold of the alpha 1-alpha 2-alpha 3(10)-alpha 3 topology, and the SF3a60 fragment forms an amphipathic alpha helix intimately contacting all of SURP2. We also solved the SURP1 structure, which has the same fold as SURP2. The protein-binding interface of SURP2 is quite similar to the corresponding surface of SURP1, except for two amino acid residues. One of them, Leu169, is characteristic of SF3a120 SURP2 among SURP domains. Mutagenesis showed that this single Leu residue is the critical determinant for complex formation, which reveals the protein recognition mechanism in the subunit assembly.

The Dugesia japonica vasa-like gene B (DjVLGB) protein is a DEAD-box RNA helicase of a planarian.. which is well known for its strong regenerative capacity. DjVLGB shares sequence similarity to the Drosophila germ-line-specific DEAD-box RNA helicase Vasa, and even higher similarity to its paralogue, mouse PL10. In this study, we solved the crystal structure of the DjVLGB N-terminal RecA-like domain. The overall fold and the structures of the putative ATPase active site of the DjVLGB N-terminal RecA-like domain are similar to those of the previously reported DEAD-box RNA helicase structures. In contrast, the surface structure of the side opposite to the putative ATPase active site is different from those of the other DEAD-box RNA helicases; the characteristic hydrophobic pockets are formed with aromatic and proline residues. These pocket-forming residues are conserved in the PL10-subfamily proteins, but less conserved in the Vasa orthologues and not conserved in the DEAD-box RNA helicases. Therefore, the structural features that we found are characteristic of the PL10-subfamily proteins and might contribute to their biological roles in germ-line development. (c) 2005 Elsevier Inc. All rights reserved.

The spliceosomal U1C protein is critical to the initiation and regulation of precursor messenger RNA (pre-mRNA) splicing, as part of the U1 small nuclear ribonucleoprotein particle (snRNP). We have produced full-length and 61 residue constructs of human U1C in soluble form in Escherichia coli. Atomic absorption spectroscopy and mass spectrometry show that both constructs contain one Zn atom and are monomeric. Gelmobility-shift assays showed that one molecule of recombinant U1C, either full-length or 61 residue construct, can be incorporated into the U1 snRNP core domain in the presence of U1 70k. This result is in perfect agreement with the previous experiment with U1C isolated from the HeLa U1 snRNP showing that the recombinant U1C is functionally active. We have determined the solution structure of the N-terminal 61 residue construct of U1C by NMR. A Cys(2)His(2)-type zinc finger, distinct from the TFIIIA-type, is extended at its C terminus by two additional helices. The two Zn-coordinating histidine residues are separated by a five residue loop. The conserved basic residues in the first two helices and the intervening loop may be involved in RNA binding. The opposite beta-sheet face with two surface-exposed Tyr residues may be involved in protein contacts. Both the full-length and 61 residue constructs of human U1C fail to bind RNA containing the 5' splice site sequence, in contrast to what has been reported for the Saccharomyces cerevisiae orthologue. (C) 2004 Elsevier Ltd. All rights reserved.

Many biogenic amines evoke a variety of physiological responses by acting on G protein-coupled receptors. We have determined the conformation of two acetylcholine analogs, (S) methacholine and (2S, 4R, 5S)-muscarine, bound to the M-2 muscarinic acetylcholine receptor (M-2 mAChR) by NMR spectroscopy. The analysis of the transferred nuclear Overhauser effect indicated that the receptor selectively recognized the conformers of (S)-methacholine and (2S, 4R, 5S)-muscarine with the gauche O-C2-C1-N dihedral angle at +60degrees. This is distinct from the predominant conformations of these ligands in solution with O-C2-C1-N dihedral angle (+80similar to85degrees) in the absence of the M-2 mAChR, as assessed by analyses of the coupling constants and nuclear Overhauser effect spectroscopy. We have also built a molecular model of the M-2 mAChR-(S)-methacholine complex, based on the X-ray crystallographic structure of rhodopsin. This model indicated that the conformation with the gauche O-C2-C1-N dihedral angle at +55.5degrees, which is similar to the one determined by NMR measurement, is energetically favored in the binding of (S)-methacholine to the receptor. We suggest that this conformation represents the binding of the agonist to the M-2 mAChR in the absence of G protein.

In the second step of the two consecutive transesterifications of the self-splicing reaction of the group I intron, the conserved guanosine at the 31 terminus of the intron (omegaG) binds to the guanosine-binding site (GBS) in the intron. In the present study, we designed a 22-nt model RNA (GBS/omegaG) including the GBS and omegaG from the Tetrahymena group I intron, and determined the solution structure by NMR methods. In this structure, omegaG is recognized by the formation of a base triple with the G2649.C311 base pair, and this recognition is stabilized by the stacking interaction between omegaG and C262. The bulged structure at A263 causes a large helical twist angle (40 +/- 8degrees) between the G264.C311 and C262.G312 base pairs. We named this type of binding pocket with a bulge and a large twist, formed on the major groove, a "Bulge-and-Twist" (BT) pocket. With another twist angle between the C262.G312 and G413.C313 base pairs (45 +/- 10degrees), the axis of GBS/omegaG is kinked at the GBS region. This kinked axis superimposes well on that of the corresponding region in the structure model built on a 5.0 Angstrom resolution electron density map (Golden et al., Science, 1998, 282:345-358). This compact structure of the GBS is also consistent with previous biochemical studies on group I introns. The BT pockets are also found in the arginine-binding site of the HIV-TAR RNA, and within the 16S rRNA and the 23S rRNA.