Mitsuaki Hirose

A kinetically controlled self-organization system was realized using the synthetically simple molecule 4,6-O-pyrenylidene glucose (Py-Glc).

Abstract The N-acetyl (NAc) group of N-acetyl glucosamine (GlcNAc) in the core structure of N-glycans is believed to stabilize their folded conformation. In this study, we synthesized Man3GlcNAc2, the common structural motif of N-glycan, bearing NAc groups and Man3Glc2 having no NAc group to understand the differences in their folded conformations due to the presence or absence of NAc group using 2D-NMR analysis. In Man3GlcNAc2, the branched α1-6Man was found to be positioned closer to the core sugar residue compared to Man3Glc2.

Metalated tetrapyrrole molecules play crucial roles in respiration, photosynthesis, and biocatalysis. In this study, the chelatase activity of the bacterial magnesium dechelatase homologous gene, which encodes an enzyme that extracts the central magnesium ion from chlorophyll, was demonstrated. The recombinant protein inserted metal ions, such as zinc, into methyl pyropheophorbide a, a synthetic derivative of chlorophyll a. Mutation analysis and structural modeling suggested H32, D34, and D62 as key residues involved in coordinating metal ions and facilitating proton extraction from methyl pyropheophorbide a. Chelatase activity was also found in the recombinant plant magnesium dechelatase protein. The bacterial gene complemented Escherichia coli ferrochelatase mutants. These findings provide novel insights into the mechanisms underlying chelation reactions.

Abstract Bacteriochlorophylls c and e are responsible for the main part of the light-harvesting process in chlorosome antenna systems of green sulfur bacteria and contain a methyl group at the peripheral C-20 position of their core chlorin rings. This study performed in vitro and in vivo analysis of the C-20 methyltransferase BchU derived from the green sulfur bacterium Chlorobaculum tepidum, which synthesizes bacteriochlorophyll c, to clarify the role of this enzyme in the biosynthetic pathway. Although the reaction step of BchU in the biosynthesis could not be determined by genetic analysis, enzymatic assays using various substrates showed that BchU reacts primarily with substrates after hydration of BchF and BchV at the C-3 position. The results in this study allow the proposition of a biosynthetic pathway for BChl c and e involving this enzyme.