4qdf
From Proteopedia
Crystal structure of apo KshA5 and KshA1 in complex with 1,4-30Q-CoA from R. rhodochrous
Structural highlights
FunctionKSHA5_RHORH Probably involved in the degradation of cholesterol (PubMed:21642460). In vitro, catalyzes the introduction of a 9alpha-hydroxyl moiety into the ring B of 3-ketosteroid substrates such as 1,4-androstadiene-3,17-dione (ADD), 4-androstene-3,17-dione (AD), 4-androstene-17beta-ol-3-one (testosterone), 4-pregnene-3,20-dione (progesterone), 19-nor-4-androstene-3,17-dione, 1-(5alpha)-androstene-3,17-dione, 5alpha-androstane-3,17-dione, 5beta-androstane-3,17-dione, 5alpha-androstane-17beta-ol-3-one (stanolon), 11beta-hydrocortisone, 3-oxo-23,24-bisnorcholesta-4-en-22-oate (4-BNC), 23,24-bisnorcholesta-4-ene-22-oate, 3-oxo-23,24-bisnorcholesta-1,4-dien-22-oate (1,4-BNC) and 3-oxo-23,24-bisnorcholesta-1,4-dien-22-oyl-coenzyme A thioester (1,4-BNC-CoA) (PubMed:21642460, PubMed:25049233). KshA5 has the broadest substrate range without a clear substrate preference and is active with Delta-4, Delta-1,4, 5alpha-H and 5beta-H steroids, as well as with steroids having bulky aliphatic side chains and an isopropionyl side chain at C17.[1] [2] Publication Abstract from PubMedKshA is the oxygenase component of 3-ketosteroid 9alpha-hydroxylase, a Rieske oxygenase involved in the bacterial degradation of steroids. Consistent with its role in bile acid catabolism, KshA1 from Rhodococcus rhodochrous DSM43269 had the highest apparent specificity (kcat/Km) for steroids with an isopropyl side chain at C17, such as 3-oxo-23,24-bisnorcholesta-1,4-diene-22-oate (1,4-BNC). By contrast, the KshA5 homolog had the highest apparent specificity for substrates with no C17 side chain (kcat/Km >10(5) s(-1) m(-1) for 4-estrendione, 5alpha-androstandione, and testosterone). Unexpectedly, substrates such as 4-androstene-3,17-dione (ADD) and 4-BNC displayed strong substrate inhibition (Ki S approximately 100 mum). By comparison, the cholesterol-degrading KshAMtb from Mycobacterium tuberculosis had the highest specificity for CoA-thioesterified substrates. These specificities are consistent with differences in the catabolism of cholesterol and bile acids, respectively, in actinobacteria. X-ray crystallographic structures of the KshAMtb.ADD, KshA1.1,4-BNC-CoA, KshA5.ADD, and KshA5.1,4-BNC-CoA complexes revealed that the enzymes have very similar steroid-binding pockets with the substrate's C17 oriented toward the active site opening. Comparisons suggest Tyr-245 and Phe-297 are determinants of KshA1 specificity. All enzymes have a flexible 16-residue "mouth loop," which in some structures completely occluded the substrate-binding pocket from the bulk solvent. Remarkably, the catalytic iron and alpha-helices harboring its ligands were displaced up to 4.4 A in the KshA5.substrate complexes as compared with substrate-free KshA, suggesting that Rieske oxygenases may have a dynamic nature similar to cytochrome P450. Substrate specificities and conformational flexibility of 3-ketosteroid 9alpha-hydroxylases.,Penfield JS, Worrall LJ, Strynadka NC, Eltis LD J Biol Chem. 2014 Sep 12;289(37):25523-36. doi: 10.1074/jbc.M114.575886. Epub, 2014 Jul 21. PMID:25049233[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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