{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n EPPIN (epididymal protease inhibitor) is a testis‐ and epididymis‐specific, cysteine‐rich protein that plays a dual role in the male reproductive tract. On one hand, EPPIN is a key component of a sperm surface protein complex where it binds seminal plasma proteins—most notably semenogelin—to modulate sperm motility. The binding of EPPIN to semenogelin, which occurs via a discrete C‐terminal region (with critical residues such as Cys102, Tyr107, and Phe117), appears to regulate semen liquefaction and the gradual recovery of sperm’s forward progression following ejaculation [(1,2,5)]. On the other hand, EPPIN exhibits antibacterial activity by permeabilizing bacterial membranes, an effect that is dependent on its proper disulfide bond conformation and the integrity of both its Kunitz‐type and WAP (whey acidic protein) domains [(1,3,4)]."}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n In the context of innate immunity, EPPIN belongs to a larger gene cluster of WAP motif proteins located on human chromosome 20, which includes several related protease inhibitors and antibacterial proteins. This cluster—evidenced by conservation and rapid evolutionary changes in its members—suggests that these proteins evolved from a common ancestral gene to provide a dual defence: protecting spermatozoa from microbial invaders and regulating the proteolytic events essential for sperm maturation and function [(6,7)]. \n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Moreover, genetic studies have suggested that variants in the EPPIN gene can influence semen quality and fertility, making it an attractive target not only for understanding the molecular basis of male infertility but also for the development of nonhormonal male contraceptives. Indeed, immunocontraceptive strategies targeting EPPIN have demonstrated reversible infertility in nonhuman primate models [(2,8)].\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n In summary, EPPIN (often considered together with other WAP-domain proteins such as WFDC family members) functions as a modulator of sperm motility through specific protein–protein interactions and as an innate immune effector protecting spermatozoa. Its precise regulation, structural integrity, and evolutionary diversification underscore its importance in both reproductive fitness and host defence.\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Citations:."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "8"}]}, {"type": "t", "text": "\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Suresh Yenugu, Richard T Richardson, Perumal Sivashanmugam, et al. 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