Division of Biochemical Sciences, CSIR-National Chemical Laboratory, Pune, India.
Academy of Scientific and Innovative Research (AcSIR), CSIR-National Chemical Laboratory, Pune, India.
FEBS Lett. 2018 Aug;592(15):2624-2635. doi: 10.1002/1873-3468.13174. Epub 2018 Jul 10.
Iridoid synthases belong to the family of short-chain dehydrogenase/reductase involved in the biosynthesis of iridoids. Despite having high sequence and structural homology with progesterone 5β-reductase, these enzymes exhibit differential substrate specificities. Previously, two loops, L1 and L2 at substrate-binding pocket, were suggested to be involved in generating substrate specificity. However, the structural basis of specificity determinants was elusive. Here, combining sequence and structural analysis, site-directed mutagenesis, and molecular dynamics simulations, we have shown that iridoid synthase contains two channels for substrate entry whose geometries are altered by L1-L2 dynamics, primarily orchestrated by interactions of residues Glu161 and Gly162 of L1 and Asn358 of L2. A complex interplay of these interactions confer the substrate specificity to the enzyme.
裂环烯醚萜合酶属于短链脱氢酶/还原酶家族，参与裂环烯醚萜的生物合成。尽管与孕酮 5β-还原酶具有高度的序列和结构同源性，但这些酶表现出不同的底物特异性。先前，有研究表明底物结合口袋中的两个环 L1 和 L2 参与产生底物特异性。然而，特异性决定因素的结构基础仍不清楚。在这里，我们通过序列和结构分析、定点突变和分子动力学模拟表明，裂环烯醚萜合酶包含两个底物进入通道，其几何形状通过 L1-L2 动力学改变，主要由 L1 中的残基 Glu161 和 Gly162 与 L2 中的残基 Asn358 的相互作用协调。这些相互作用的复杂相互作用赋予了酶的底物特异性。
