Flexibility of Short-chain dehydrogenase is interconnected to its promiscuity for the reduction of multiple ketone intermediates

Abstract

Short-chain dehydrogenases/reductases (SDRs) are an essential family of enzymes used to synthesize enantiopure alcohols. Several studies describe prospected or engineered candidates for converting substrates of interest using cost and time-intensive high-throughput approaches. For catalysis, SDRs are classified into five types based on chain length and cofactor binding site. Of these, the shorter Classical and the longer Extended enzymes participate in ketoreduction. However, comparative analysis of various modelled SDRs reveals a length independent conserved N-terminal Rossmann fold and a variable C-terminus region. The latter domain is hypothesized to affect the flexibility of the enzyme. We have used machine learning on this flexible domain to build a rationale to screen promiscuous SDRs. A dataset consisting of physicochemical properties derived from the amino-acid composition of enzymes is used to select closely associated promiscuous mesophilic enzymes. The resulting in vitro studies on pro-pharmaceutical substrates illustrate a direct correlation between the C-terminal lid-loop structure, enzyme melting temperature and the turnover number. We present a walkthrough for exploring promiscuous SDRs for catalyzing enantiopure alcohols of industrial importance.