5e4r
From Proteopedia
Crystal structure of domain-duplicated synthetic class II ketol-acid reductoisomerase 2Ia_KARI-DD
Structural highlights
FunctionILVC_IGNAA Involved in the biosynthesis of branched-chain amino acids (BCAA). Catalyzes an alkyl-migration followed by a ketol-acid reduction of (S)-2-acetolactate (S2AL) to yield (R)-2,3-dihydroxy-isovalerate. In the isomerase reaction, S2AL is rearranged via a Mg-dependent methyl migration to produce 3-hydroxy-3-methyl-2-ketobutyrate (HMKB). In the reductase reaction, this 2-ketoacid undergoes a metal-dependent reduction by NADPH or NADH to yield (R)-2,3-dihydroxy-isovalerate.[1] [2] Publication Abstract from PubMedThe duplication of protein structural domains has been proposed as a common mechanism for the generation of new protein folds. A particularly interesting case is the class II ketol-acid reductoisomerase (KARI), which putatively arose from an ancestral class I KARI by duplication of the C-terminal domain and corresponding loss of obligate dimerization. As a result, the class II enzymes acquired a deeply embedded figure-of-eight knot. To test this evolutionary hypothesis we constructed a novel class II KARI by duplicating the C-terminal domain of a hyperthermostable class I KARI. The new protein is monomeric, as confirmed by gel filtration and x-ray crystallography, and has the deeply-knotted class II KARI fold. Surprisingly, its catalytic activity is nearly unchanged from the parent KARI. This provides strong evidence in support of domain duplication as the mechanism for the evolution of the class II KARI fold and demonstrates the ability of domain duplication to generate topological novelty in a function-neutral manner. This article is protected by copyright. All rights reserved. Artificial domain duplication replicates evolutionary history of ketol-acid reductoisomerases.,Cahn JK, Brinkmann-Chen S, Buller AR, Arnold FH Protein Sci. 2015 Dec 8. doi: 10.1002/pro.2852. PMID:26644020[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
| ||||||||||||||||||||
