1amj: Difference between revisions

Revision as of 10:27, 2 May 2008

STERIC AND CONFORMATIONAL FEATURES OF THE ACONITASE MECHANISM

OverviewOverview

Crystal structures of mitochondrial aconitase with alpha-methylisocitrate and with sulfate bound have been solved and refined at 2.0 A resolution with R factors of 18.2 and 16.8%, respectively. The steric factors and conformational effects observed in both new structures support the proposed mechanism for the overall reaction catalyzed by aconitase. The alternate substrate alpha-methylisocitrate is derived from alpha-methyl-cis-aconitate during crystallization and is observed to bind in the active site in a manner very similar to that observed for isocitrate. The methyl group is accommodated by favorable contact with Ile-425. However, the other potential hydration product of alpha-methyl-cis-aconitate, alpha-methylcitrate, cannot be accommodated in the active site due to steric conflict of the methyl group with Asp-165. The results are consistent with the requirement that cis-aconitate must bind in two ways, in the citrate mode and in the isocitrate mode. Crystals of aconitase with sulfate bound are isomorphous to those with isocitrate bound. However, the structure displays significant conformational changes, providing a model for the substrate-free state of enzyme. Three water molecules bind in place of the C alpha- and C beta-hydroxyl and carboxyl groups of isocitrate, while sulfate binds in place of the C gamma-carboxyl group. Side chains of Ser-642 and Arg-447 in the active site rotate to pair with other side chains in the absence of substrate. The new conformation of Arg-447 triggers a concerted set of shifts which transmits conformational change to the surface of the protein, 30 A from the active site. In the absence of substrate, a chain segment containing the [4Fe-4S] ligand Cys-358 also shifts, resulting in the net translation and reorientation of the Fe-S cluster.

About this StructureAbout this Structure

1AMJ is a Single protein structure of sequence from Bos taurus. Full crystallographic information is available from OCA.

ReferenceReference

Steric and conformational features of the aconitase mechanism., Lauble H, Stout CD, Proteins. 1995 May;22(1):1-11. PMID:7675781 Page seeded by OCA on Fri May 2 10:27:04 2008

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OCA

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 [[Image:1amj.gif|left|200px]]
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 '''STERIC AND CONFORMATIONAL FEATURES OF THE ACONITASE MECHANISM'''
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 [[Category: Single protein]]
 [[Category: Stout, C D.]]
-[[Category: lyase(carbon-oxygen)]]
+''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May  2 10:27:04 2008''
-''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Mar 30 18:43:25 2008''