In silico docking analysis of beta-defensin 20 against cation channel sperm-associated protein 1-4 to predict its role in the sperm maturation

Abstract

Beta-defensin 20 (DEFB20) is widely expressed in the epididymis with gene features involved in epididymal sperm maturation. However, the action mechanism and function of DEFB20 in sperm maturation are still unclear. One of the important roles of beta-defensin is the ion channel activity. The cation channel sperm-associated protein (CatSper) alpha is an ion channel protein found on the sperm surface. This study aimed to investigate the interaction between DEFB20 and CatSper1-4 protein in relation to the sperm maturation process. Protein sequences were obtained from the National Center for Biotechnology Information (NCBI). Protein modeling and validation were carried out by using the Robetta modeling server and the Ramachandran plot method. Rosetta web server was used for the docking analysis. The results revealed a natural interaction between DEFB20 and CatSper1-4. The interaction occurred at the cation channel (close to the casein kinase II), ion transport protein, and kinase c phosphorylation of the CatSper1-4 active site. The DEFB20 region interacting with CatSper2-4 was the beta-defensin domain, while with CatSper1 was the non-beta-defensin domain. Based on the analysis, DEFB20 may interact with CatSper α subunits, particularly CatsSper1, to affect ion channel activity during sperm maturation.

Keywords: CatSper; DEFB20; docking; sperm maturation.

Figure 1

The 3D structures of DEFB20 and CatSper1–4: (a) CatSper1, (b) CatSper2, (c) CatSper3 isoform 1, (d) CatSper3 isoform 2, (e) CatSper3 isoform 3, (f) CatSper4 isoform 1, (g) CatSper4 isoform 2, and (h) DEFB20. DEFB20: beta-defensin 20; CatSper: the cation channel sperm-associated protein; 3D: three-dimensional.

Figure 2

Molecular docking visuals of DEFB20 and CatSper1–4. (a) Interaction between Arg310, Ala313, and Gln314 from CatSper1 has hydrophobic interaction with K61 in DEFB20. (b) Glu569 from CatSper2 (model 2) has an interaction hydrogen bond with Leu38 in DEFB20 and hydrophobic interaction in position Arg37. (c) Lys573 from CatSper2 (model 4) has hydrophobic interaction with Leu38 in DEFB20. (d) Ser16 and Ser17 from CatSper3 isoform 1 have hydrophobic interaction with Arg28 and Leu38 in DEFB20. Ser16 in CatSper3 isoform 1 has hydrogen bond with Leu38 in DEFB20. (e) Ile114, Leu117, Leu118, and Ile121 from CatSper3 isoform 2 have hydrophobic interaction with Asn27, Ser26, and Phe25 in DEFB20. (f) Ser265, Met266, Asp270, Glu273, and Lys277 from CatSper3 isoform 3 have hydrophobic interaction with Phe25, Ser26, Asn27, Cys45, Leu47, and His48 in DEFB20. (g) Tyr253 and Ala254 from CatSper4 isoform 1 have hydrophobic interaction with Leu38 and Arg37 in DEFB20. (h) Glu235, Asp236, and Thr240 from CatSper4 isoform 2 have hydrophobic interaction with Asn27, Val28, and Glu29 in DEFB20. Hydrogen bonds occur in Thr240 of CatSper4 isoform 2 Asn27 in DEFB20. DEFB20: beta-defensin 20; CatSper: the cation channel sperm-associated protein; Glu: glutamic acid; Leu: leucine; Arg: arginine; Lys: lysine; Ser: serine; Ile: isoleucine; Gln: glutamine; Met: methionine; Tyr: tyrosine; Phe: phenylalanine; Asn: asparagine; Cys: cysteine; His: histidine; Thr: threonine; Val: valine.