1szo
Crystal Structure Analysis of the 6-Oxo Camphor Hydrolase His122Ala Mutant Bound to Its Natural Product (2S,4S)-alpha-Campholinic Acid
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OverviewOverview
The crotonase homolog, 6-oxo camphor hydrolase (OCH), catalyzes the, desymmetrization of bicyclic beta-diketones to optically active keto acids, via an enzymatic retro-Claisen reaction, resulting in the cleavage of a, carbon-carbon bond. We have previously reported the structure of OCH, (Whittingham, J. L., Turkenburg, J. P., Verma, C. S., Walsh, M. A., and, Grogan, G. (2003) J. Biol. Chem. 278, 1744-1750), which suggested the, involvement of five residues, His-45, His-122, His-145, Asp-154, and, Glu-244, in catalysis. Here we report mutation studies on OCH that reveal, that H145A and D154N mutants of OCH have greatly reduced values of, k(cat)/K(m) derived from a very large increase in K(m) for the native, substrate, 6-oxo camphor. In addition, H122A has a greatly reduced value, of k(cat), and its K(m) is five times that of the wild-type. The location, of the active site is confirmed by the 1.9-A structure of the H122A mutant, of OCH complexed with the minor diastereoisomer of, (2S,4S)-alpha-campholinic acid, the natural product of the enzyme. This, shows the pendant acetate of the product hydrogen bonded to a, His-145/Asp-154 dyad and the endocyclic carbonyl of the cyclopentane ring, hydrogen bonded to Trp-40. The results are suggestive of a base-catalyzed, mechanism of C-C bond cleavage and provide clues to the origin of, prochiral selectivity by the enzyme and to the recruitment of the, crotonase fold for alternate modes of transition state stabilization to, those described for other crotonase superfamily members.
About this StructureAbout this Structure
1SZO is a Single protein structure of sequence from Rhodococcus sp. ncimb 9784 with CA and CAX as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Structure of 6-oxo camphor hydrolase H122A mutant bound to its natural product, (2S,4S)-alpha-campholinic acid: mutant structure suggests an atypical mode of transition state binding for a crotonase homolog., Leonard PM, Grogan G, J Biol Chem. 2004 Jul 23;279(30):31312-7. Epub 2004 May 11. PMID:15138275
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