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1x1d

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{{STRUCTURE_1x1d| PDB=1x1d | SCENE= }}
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'''Crystal structure of BchU complexed with S-adenosyl-L-homocysteine and Zn-bacteriopheophorbide d'''
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===Crystal structure of BchU complexed with S-adenosyl-L-homocysteine and Zn-bacteriopheophorbide d===
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==Overview==
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BchU plays a role in bacteriochlorophyll c biosynthesis by catalyzing methylation at the C-20 position of cyclic tetrapyrrole chlorin using S-adenosylmethionine (SAM) as a methyl source. This methylation causes red-shifts of the electronic absorption spectrum of the light-harvesting pigment, allowing green photosynthetic bacteria to adapt to low-light environments. We have determined the crystal structures of BchU and its complex with S-adenosylhomocysteine (SAH). BchU forms a dimer and each subunit consists of two domains, an N-terminal domain and a C-terminal domain. Dimerization occurs through interactions between the N-terminal domains and the residues responsible for the catalytic reaction are in the C-terminal domain. The binding site of SAH is located in a large cavity between the two domains, where SAH is specifically recognized by many hydrogen bonds and a salt-bridge. The electron density map of BchU in complex with an analog of bacteriochlorophyll c located its central metal near the SAH-binding site, but the tetrapyrrole ring was invisible, suggesting that binding of the ring to BchU is loose and/or occupancy of the ring is low. It is likely that His290 acts as a ligand for the central metal of the substrate. The orientation of the substrate was predicted by simulation, and allows us to propose a mechanism for the BchU directed methylation: the strictly conserved Tyr246 residue acts catalytically in the direct transfer of the methyl group from SAM to the substrate through an S(N)2-like mechanism.
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{{ABSTRACT_PUBMED_16797589}}
==About this Structure==
==About this Structure==
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Jul 27 18:53:15 2008''

Revision as of 15:53, 27 July 2008

Image:1x1d.png

Template:STRUCTURE 1x1d

Crystal structure of BchU complexed with S-adenosyl-L-homocysteine and Zn-bacteriopheophorbide d

Template:ABSTRACT PUBMED 16797589

About this Structure

1X1D is a Single protein structure of sequence from Chlorobaculum tepidum. Full crystallographic information is available from OCA.

Reference

Crystal structures of BchU, a methyltransferase involved in bacteriochlorophyll c biosynthesis, and its complex with S-adenosylhomocysteine: implications for reaction mechanism., Wada K, Yamaguchi H, Harada J, Niimi K, Osumi S, Saga Y, Oh-Oka H, Tamiaki H, Fukuyama K, J Mol Biol. 2006 Jul 21;360(4):839-49. Epub 2006 Jun 8. PMID:16797589

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