Evidence that a functional fertilin-like ADAM plays a role in human sperm-oolemmal interactions

Fertilin is a protein initially identified in guinea pig spermatozoa; it is the prototype of a larger family of conserved proteins designated as a dis integrin and a metalloproteinase (ADAM). These heterodimers which consist o f alpha and beta subunits, containing metalloproteinase-like and disintegri n-like domains, appear to play a role in mammalian fertilization. Peptides derived from the disintegrin domains of two ADAMs, fertilin and cyritestin, interfere with gamete adhesion and sperm-egg membrane fusion in non-human species. It has been suggested that fertilin-beta binds to an oolemmal inte grin, and it is proposed that the tripeptide FEE (Phe-Glu-Glu) is the integ rin recognition sequence in human fertilin-beta. We evaluated whether ferti lin beta plays a role in human fertilization by studying the effects of a l inear octapeptide containing the FEE sequence, SFEECDLP, and a scrambled oc tapeptide with the same amino acids, SFPCEDEL, on the incorporation of huma n spermatozoa by human zona-free eggs. The effects of G4120, a potent RGD-c ontaining (Arg-Gly-Asp) thioether-bridged cyclic peptide which blocks both fibronectin and vitronectin receptors, and the relationship between FEE- an d RGD-receptor interactions on sperm-egg interactions were also studied. Th e FEE-containing peptide, but not the scrampled peptide, inhibited sperm ad hesion to oocytes and their penetration, over the range 1-5 mu M The inhibi tion induced by SFEECDLP was reversible and occurred only in the presence o f peptide itself. The G4120 peptide exhibited 10-fold less inhibitory effec ts on sperm adhesion and penetration than did SFEECDLP. When combined, SFEE CDLP and G4120 exhibited strong inhibition of both adhesion and penetration at concentrations that individually had been ineffective, suggesting co-op eration between the two receptor-ligand interactions during fertilization. We propose that a fertilin-like molecule is functionally active on human sp ermatozoa and that its interaction with an oolemmal integrin receptor plays a role in fertilization in humans.