Kobilka Institute of Innovative Drug Discovery, School of Life and Health Sciences, The Chinese University of Hong Kong, Shenzhen, Guangdong, 518172, China.
State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai, 200031, China.
Nat Commun. 2021 Jan 19;12(1):449. doi: 10.1038/s41467-020-20675-2.
Steroid hormones are essential in stress response, immune system regulation, and reproduction in mammals. Steroids with 3-oxo-Δ structure, such as testosterone or progesterone, are catalyzed by steroid 5α-reductases (SRD5As) to generate their corresponding 3-oxo-5α steroids, which are essential for multiple physiological and pathological processes. SRD5A2 is already a target of clinically relevant drugs. However, the detailed mechanism of SRD5A-mediated reduction remains elusive. Here we report the crystal structure of PbSRD5A from Proteobacteria bacterium, a homolog of both SRD5A1 and SRD5A2, in complex with the cofactor NADPH at 2.0 Å resolution. PbSRD5A exists as a monomer comprised of seven transmembrane segments (TMs). The TM1-4 enclose a hydrophobic substrate binding cavity, whereas TM5-7 coordinate cofactor NADPH through extensive hydrogen bonds network. Homology-based structural models of HsSRD5A1 and -2, together with biochemical characterization, define the substrate binding pocket of SRD5As, explain the properties of disease-related mutants and provide an important framework for further understanding of the mechanism of NADPH mediated steroids 3-oxo-Δ reduction. Based on these analyses, the design of therapeutic molecules targeting SRD5As with improved specificity and therapeutic efficacy would be possible.
甾体激素在哺乳动物的应激反应、免疫系统调节和生殖中起着至关重要的作用。具有 3-氧代-Δ 结构的甾体激素，如睾酮或孕酮，可被甾体 5α-还原酶（SRD5As）催化生成相应的 3-氧代-5α 甾体激素，这对于多种生理和病理过程都是必不可少的。SRD5A2 已经是临床相关药物的靶点。然而，SRD5A 介导的还原的详细机制仍不清楚。在这里，我们报道了来自变形菌门细菌的 PbSRD5A 的晶体结构，它是 SRD5A1 和 SRD5A2 的同源物，与辅因子 NADPH 的复合物分辨率为 2.0Å。PbSRD5A 以单体形式存在，由七个跨膜片段（TMs）组成。TM1-4 包围着一个疏水性的底物结合腔，而 TM5-7 通过广泛的氢键网络与辅因子 NADPH 配位。基于结构同源性的 HsSRD5A1 和 -2 的模型，以及生化特性的研究，定义了 SRD5As 的底物结合口袋，解释了与疾病相关的突变体的性质，并为进一步理解 NADPH 介导的甾体 3-氧代-Δ 还原的机制提供了重要框架。基于这些分析，可以设计出针对 SRD5As 的治疗性分子，以提高特异性和治疗效果。
