Shan Changyu, Li Hongwei, Zhang Yuping, Li Yuyan, Chen Yingchun, He Wei
Department of Pharmaceutical Chemistry, The Third Military Medical University, Chongqing, China.
College of Pharmacy and Bioengineering, Chongqing University of Technology, Chongqing, China.
PeerJ. 2019 Aug 5;7:e7329. doi: 10.7717/peerj.7329. eCollection 2019.
Epididymal protease inhibitor (EPPIN) that is located on the sperm surface and specific to the male reproductive system is a non-hormonal contraceptive target, since the binding of EPPIN with the seminal plasma protein semenogelin-1 (SEMG1) causes a loss of sperm function. Here, we investigated the binding interactions between EPPIN and SEMG1 by homology modeling, docking and molecular dynamics simulation. Since no crystal structure was reported for EPPIN, its 3D structure was constructed by homology modeling and refined by dynamics simulation, illustrating the C-terminus domain of EPPIN could bind with its N-terminus domain through the residues 30-32 and 113-116. The binding interaction of SEMG1 peptide and EPPIN was investigated by Z-DOCK and dynamics simulation. After evaluating the models according to the calculated binding free energies, we demonstrated that C-terminus domain of EPPIN was important for the binding of SEMG1 via residues Tyr107, Gly112, Asn116, Gln118 and Asn122, while residue Arg32 in N-terminus domain also had contribution for their binding interaction. Additionally, the binding pocket of EPPIN was defined according to these key residues and verified by molecular docking with reported inhibitor , suggesting that the pocket formed by Arg32, Asn114, Asn116, Phe117 and Asn122 could be important for the design of new ligands. This study might be helpful for the understanding of biological function of EPPIN and would encourage the discovery of non-hormonal contraceptive leads/drugs in the future.
附睾蛋白酶抑制剂（EPPIN）位于精子表面，对男性生殖系统具有特异性，是一种非激素避孕靶点，因为EPPIN与精浆蛋白精液凝素-1（SEMG1）的结合会导致精子功能丧失。在此，我们通过同源建模、对接和分子动力学模拟研究了EPPIN与SEMG1之间的结合相互作用。由于尚未报道EPPIN的晶体结构，我们通过同源建模构建了其三维结构，并通过动力学模拟进行了优化，结果表明EPPIN的C末端结构域可通过30 - 32位和113 - 116位残基与其N末端结构域结合。通过Z - DOCK和动力学模拟研究了SEMG1肽与EPPIN的结合相互作用。根据计算得到的结合自由能对模型进行评估后，我们证明EPPIN的C末端结构域对于SEMG1通过Tyr107、Gly112、Asn116、Gln118和Asn122残基的结合很重要，而N末端结构域中的Arg32残基对它们的结合相互作用也有贡献。此外，根据这些关键残基定义了EPPIN的结合口袋，并通过与报道的抑制剂进行分子对接进行了验证，这表明由Arg32、Asn114、Asn116、Phe117和Asn122形成的口袋对于新配体的设计可能很重要。这项研究可能有助于理解EPPIN的生物学功能，并有望在未来促进非激素避孕先导物/药物的发现。
