1x1a
From Proteopedia
(New page: 200px<br /><applet load="1x1a" size="450" color="white" frame="true" align="right" spinBox="true" caption="1x1a, resolution 2.60Å" /> '''Crystal structure of...) |
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| - | [[Image:1x1a.gif|left|200px]]<br /><applet load="1x1a" size=" | + | [[Image:1x1a.gif|left|200px]]<br /><applet load="1x1a" size="350" color="white" frame="true" align="right" spinBox="true" |
caption="1x1a, resolution 2.60Å" /> | caption="1x1a, resolution 2.60Å" /> | ||
'''Crystal structure of BchU complexed with S-adenosyl-L-methionine'''<br /> | '''Crystal structure of BchU complexed with S-adenosyl-L-methionine'''<br /> | ||
==Overview== | ==Overview== | ||
| - | BchU plays a role in bacteriochlorophyll c biosynthesis by catalyzing | + | 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. |
==About this Structure== | ==About this Structure== | ||
| - | 1X1A is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Chlorobaculum_tepidum Chlorobaculum tepidum] with SO4, SAM and GOL as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http:// | + | 1X1A is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Chlorobaculum_tepidum Chlorobaculum tepidum] with <scene name='pdbligand=SO4:'>SO4</scene>, <scene name='pdbligand=SAM:'>SAM</scene> and <scene name='pdbligand=GOL:'>GOL</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1X1A OCA]. |
==Reference== | ==Reference== | ||
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[[Category: sam]] | [[Category: sam]] | ||
| - | ''Page seeded by [http:// | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 15:50:04 2008'' |
Revision as of 13:50, 21 February 2008
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Crystal structure of BchU complexed with S-adenosyl-L-methionine
Overview
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.
About this Structure
1X1A is a Single protein structure of sequence from Chlorobaculum tepidum with , and as ligands. 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
Page seeded by OCA on Thu Feb 21 15:50:04 2008
Categories: Chlorobaculum tepidum | Single protein | Fukuyama, K. | Wada, K. | Yamaguchi, H. | GOL | SAM | SO4 | Ado-hcy | Ado-met | Bacteriochllochlorophyll | Bchu | Methyltransferase | S-adenosylhomocysteine | S-adenosylmethyonine | Sah | Sam
