2e0n
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(New page: 200px<br /><applet load="2e0n" size="350" color="white" frame="true" align="right" spinBox="true" caption="2e0n, resolution 2.00Å" /> '''Crystal structure of...)
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Revision as of 17:15, 29 January 2008
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Crystal structure of CbiL in complex with S-adenosylhomocysteine, a methyltransferase involved in anaerobic vitamin B12 biosynthesis
Overview
During anaerobic cobalamin (vitamin B12) biosynthesis, CbiL catalyzes, methylation at the C-20 position of a cyclic tetrapyrrole ring using, S-adenosylmethionine 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 a catalytic, mechanism: the conserved Tyr226 residue in CbiL catalyzes the direct, transfer of a methyl group from S-adenosylmethionine to the substrate, through an S(N)2-like mechanism. Furthermore, the structural model of CbiL, binding to its substrate suggests the axial residue coordinated to the, central cobalt of cobalt-factor II.
About this Structure
2E0N is a Single protein structure of sequence from Chlorobaculum tepidum with as ligand. Active as Precorrin-2 C(20)-methyltransferase, with EC number 2.1.1.130 Full crystallographic information is available from OCA.
Reference
Crystal structures of CbiL, a methyltransferase involved in anaerobic vitamin B biosynthesis, and CbiL in complex with S-adenosylhomocysteine--implications for the reaction mechanism., Wada K, Harada J, Yaeda Y, Tamiaki H, Oh-Oka H, Fukuyama K, FEBS J. 2007 Jan;274(2):563-73. PMID:17229157
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