tailieunhanh - Báo cáo khoa học: Crystal structures of CbiL, a methyltransferase involved in anaerobic vitamin B12 biosynthesis, and CbiL in complex with S-adenosylhomocysteine ) implications for the reaction mechanism

During anaerobic cobalamin (vitamin B12) biosynthesis, CbiL catalyzes methylation at the C-20 position of a cyclic tetrapyrrole ring usingS-aden-osylmethionine as a methyl group source. This methylation is a key modifi-cation for the ring contraction process, by which a porphyrin-type tetrapyrrole ring is converted to a corrin ring through elimination of the modified C-20 and direct bonding of C-1 to C-19. | ỊFEBS Journal Crystal structures of CbiL a methyltransferase involved in anaerobic vitamin B12 biosynthesis and CbiL in complex with S-adenosylhomocysteine - implications for the reaction mechanism Kei Wada1 Jiro Harada2 Yuki Yaeda2 Hitoshi Tamiaki2 Hirozo Oh-oka1 and Keiichi Fukuyama1 1 Department of BiologicalSciences Graduate Schoolof Science Osaka University Toyonaka Japan 2 Department of Bioscience and Biotechnology Faculty of Science and Engineering Ritsumeikan University Kusatsu Shiga Japan Keywords BchU Chlorobium tepidum cobalamin precorrin-2 SN2-reaction Correspondence K. Wada Department of Biological Sciences Graduate School of Science Osaka University Osaka 560-0043 Japan Fax 81 6 6850 5425 Tel 81 6 6850 5423 E-mail keiwada@ Received 21 October 2006 revised 18 November 2006 accepted 21 November 2006 doi During anaerobic cobalamin vitamin B12 biosynthesis CbiL catalyzes methylation at the C-20 position of a cyclic tetrapyrrole ring using S-aden-osylmethionine as a methyl group source. This methylation is a key modification for the ring contraction process by which a porphyrin-type tetrapyrrole ring is converted to a corrin ring through elimination of the modified C-20 and direct bonding of C-1 to C-19. We have determined the crystal structures of Chlorobium tepidum CbiL and CbiL in complex with S-adenosylhomocysteine the S-demethyl form of S-adenosylmethionine . CbiL forms a dimer in the crystal and each subunit consists of N-terminal and C-terminal domains. S-Adenosylhomocysteine binds to a cleft between the two domains where it is specifically recognized by extensive hydrogen bonding and van der Waals interactions. The orientation of the cobalt-factor II substrate was modeled by simulation and the predicted model suggests that the hydroxy group of Tyr226 is located in close proximity to the C-20 atom as well as the C-1 and C-19 atoms of the tetrapyrrole ring. These configurations allow us to propose

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