title: Substrate-dependent stereospecificity of Tyl-KR1: an isolated polyketide synthase ketoreductase domain from Streptomyces fradiae.
abstract: The stereospecificity of an enzymatic reaction depends on the way in which a substrate and its enantiomer bind to the active site. These binding modes cannot be easily predicted. We have studied the stereospecificity and stereoselectivity of the ketoreductase domain Tyl-KR1 of the tylactone polyketide synthase from Streptomyces fradiae by analysing the stereochemical outcome of the reduction of five different keto ester substrates. The absolute configuration of the Tyl-KR1 reduction products was determined by using vibrational circular dichroism (VCD) spectroscopy combined with quantum chemical calculations. The conversion of only one of the tested substrates, 2-methyl-3-oxovaleric acid N-acetylcysteamine thioester, afforded the expected anti-(2R,3R) configuration of the α-methyl-β-hydroxyl ester product, representing the stereochemistry observed for the physiological polyketide product tylactone. For all other substrates, which were modified with respect to the type of ester and/or the chain length (C4 instead of C5), the opposite configuration (anti-(2S,3S)) was obtained with significant enantio- and diastereoselectivity. Inversion of both stereocentres suggests completely different binding modes invoked by only minor modifications of the substrate structure.
authors.affiliation: Institute of Pharmaceutical Sciences, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104 Freiburg, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Häckh
authors.forename: Michael
authors.initials: M
authors.lastname: Müller
authors.forename: Steffen
authors.initials: S
authors.lastname: Lüdeke
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D020134:Catalytic Domain; D010421:Pentanoic Acids / Q000737:chemistry; D048630:Polyketide Synthases / Q000737:chemistry*; D061065:Polyketides / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D013237:Stereoisomerism; D013302:Streptomyces / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D010421:Pentanoic Acids; D061065:Polyketides; C017517:2-methyl-3-oxovaleric acid; D048630:Polyketide Synthases; D000429:Alcohol Oxidoreductases; C087192:polyketide synthase ketoreductase