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1iwb
From Proteopedia
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'''Crystal structure of diol dehydratase''' | '''Crystal structure of diol dehydratase''' | ||
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[[Category: Toraya, T.]] | [[Category: Toraya, T.]] | ||
[[Category: Yasuoka, N.]] | [[Category: Yasuoka, N.]] | ||
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| - | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 20:30:05 2008'' | |
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Revision as of 17:30, 2 May 2008
Crystal structure of diol dehydratase
Overview
Substrate binding triggers catalytic radical formation through the cobalt-carbon bond homolysis in coenzyme B12-dependent enzymes. We have determined the crystal structure of the substrate-free form of Klebsiella oxytoca diol dehydratase*cyanocobalamin complex at 1.85 A resolution. The structure contains two units of the heterotrimer consisting of alpha, beta, and gamma subunits. As compared with the structure of its substrate-bound form, the beta subunits are tilted by approximately 3 degrees and cobalamin is also tilted so that pyrrole rings A and D are significantly lifted up toward the substrate-binding site, whereas pyrrole rings B and C are only slightly lifted up. The structure revealed that the potassium ion in the substrate-binding site of the substrate-free enzyme is also heptacoordinated; that is, two oxygen atoms of two water molecules coordinate to it instead of the substrate hydroxyls. A modeling study in which the structures of both the cobalamin moiety and the adenine ring of the coenzyme were superimposed onto those of the enzyme-bound cyanocobalamin and the adenine ring-binding pocket, respectively, demonstrated that the distortions of the Co-C bond in the substrate-free form are already marked but slightly smaller than those in the substrate-bound form. It was thus strongly suggested that the Co-C bond becomes largely activated (labilized) when the coenzyme binds to the apoenzyme even in the absence of substrate and undergoes homolysis through the substrate-induced conformational changes of the enzyme. Kinetic coupling of Co-C bond homolysis with hydrogen abstraction from the substrate shifts the equilibrium to dissociation.
About this Structure
1IWB is a Protein complex structure of sequences from Klebsiella oxytoca. Full crystallographic information is available from OCA.
Reference
Substrate-induced conformational change of a coenzyme B12-dependent enzyme: crystal structure of the substrate-free form of diol dehydratase., Shibata N, Masuda J, Morimoto Y, Yasuoka N, Toraya T, Biochemistry. 2002 Oct 22;41(42):12607-17. PMID:12379103 Page seeded by OCA on Fri May 2 20:30:05 2008
