Abstract
Short-chain dehydrogenases/reductases (SDRs) are one of the most prevalent enzyme families distributed among the sequenced microorganisms. Despite the presence of a conserved catalytic tetrad and high structural similarity, these enzymes exhibit different substrate specificities. The insufficient knowledge regarding the amino acids underlying substrate specificity hinders the understanding of the SDRs' roles in diverse and significant biological processes. Here, we performed bioinformatic analysis, molecular modeling, and mutagenesis studies to identify the key residues that regulate the substrate specificities of two homologous microbial SDRs (i.e., DesE and KduD). Further, we investigated the impact of altering the physicochemical properties of these amino acids on enzyme activity. Interestingly, molecular dynamics simulations also suggest a critical role of enzyme conformational flexibility in substrate recognition and catalysis. Overall, our findings improve the understanding of microbial SDR substrate specificity and shed light on future rational design of more efficient and effective biocatalysts.