Human sperm–egg binding is inhibited by peptides corresponding to core region of an acrosomal serine protease inhibitor

Abstract

An antiserum, designated R4 and raised against denatured hamster acrosomes, was shown to localize specifically to the acrosomal region of hamster, rat, mouse, and human spermatozoa, and to inhibit both hamster and human sperm-oocyte binding in vitro. Following screening of a human testis lambda gt11 cDNA expression library with the antiserum R4, a series of cDNA clones were isolated. One (cDNA 134) was selected based on the ability of the beta-galactosidase fusion protein to inhibit human and hamster sperm-zona binding in vitro. The fusion protein was also shown to inhibit the penetration of zona-free hamster oocytes by human spermatozoa. Sequence analysis revealed that cDNA 134 coded for a portion of a serine protease inhibitor (serpin) closely related to plasma Protein C inhibitor. Sequencing of an additional cDNA clone (261) and Northern blot analysis confirmed that a Protein C inhibitor-like mRNA is synthesised in the human testis. Affinity-purified anti-134 antibody specifically localized to the acrosomal region of both hamster and human sperm. Synthetic peptides corresponding to the conserved core region responsible for the interaction of the serpin with its cognate protease also blocked human sperm-zona binding in vitro. The results suggest that this acrosomally located inhibitor plays an important role in the series of binding events that results in human fertilization.

Protein C Inhibitor Secreted from Activated Platelets Efficiently Inhibits Activated Protein C on Phosphatidylethanolamine of Platelet Membrane and Microvesicles

“…Plasma PCI seems to be produced mainly in the liver because the plasma level of PCI decreased in patients with severe liver diseases (14). Recently, PCI was detected in human seminal plasma, Graaf follicular fluid, testis, epididymis, prostate, seminal vesicle (15), and the preacrosomal region of human spermatozoa (16,17). PCI was found previously to inhibit acrosin, a serine protease localized in the acrosome of spermatozoa (17,18).…”

Polymorphisms in the protein C inhibitor gene in in vitro fertilization failure

“…In humans, PCI is expressed in different organs and tissues; the highest PCI concentration occurs in seminal plasma (11) and in seminal vesicle secretions (12). The PCI has also been shown to be present in the testis and the prostate and on the acrosomal cap of human sperm (13). Some studies have also suggested that PCI could play a role in male fertility (reviewed in Ref.…”

Characterization of Semenogelin II and its Molecular interaction with Prostate‐Specific Antigen and Protein C Inhibitor

“…Interestingly, the level of seminal plasma PCI was found to be low in some infertile men 115, 161. In contrast, PCI was also reported to inhibit the serine protease acrosin [19], present in the acrosome of spermatozoa as well as the binding of the spermatozoa to oocytes [17], suggesting a potential role for PCI in the regulation of fertilization.Ejaculated human semen is composed of seminal vesicle secretion (seminal fluid), prostatic fluid, and epididymal fluid containing the spermatozoa. The seminal fluid is composed of a gelatinous coagula containing two major proteins, semenogelins I (Sg I, 52 kDa) and 11 (Sg 11, 71-76 kDa).…”

“…Interestingly, the level of seminal plasma PCI was found to be low in some infertile men 115, 161. In contrast, PCI was also reported to inhibit the serine protease acrosin [19], present in the acrosome of spermatozoa as well as the binding of the spermatozoa to oocytes [17], suggesting a potential role for PCI in the regulation of fertilization.…”

“…Prostate-specific antigen, semenogelase ( -3.9 pM), partly forming a complex with a serine protease, prostate-specific antigen (PSA). PCI has also been described to be present in the Graaf follicular fluid, testis, epididymis, prostate, seminal vesicle [15,161, and acrosomal regions of human spermatozoa [17,181. Interestingly, the level of seminal plasma PCI was found to be low in some infertile men 115, 161.…”