Inhibition of human spermatozoa-zona pellucida binding by a combinatorially derived peptide from a synthetic target.

Intact zona-free human oocytes were screened using a combinatorial peptide library selection protocol. Pieczenik Peptide Sequence 1 (PPS1) HEHRKRG binds human spermatozoa. A complementary and unique binding sequence HNSSLSPLATPA (PPS2) was developed from the first PPS1 ligand that binds to the human zona pellucida or oolemma. Cytoplasm-free zonae from unfertilized eggs were obtained and used as an assay system to test the effects of exposure to these two ligands. Spermatozoa were inserted into evacuated zonae and their behaviour and binding activity were assessed at regular intervals. The behaviour of spermatozoa exposed to PPS1 and unlabelled spermatozoa injected into unexposed zonae was similar as far as binding was concerned (50 and 54% binding), but PPS1 exposed spermatozoa had higher motility and displacement, marked by their escape from the zona pellucida. Zonae exposed to PPS2 inhibited the interaction between injected spermatozoa and the inside of the zona when compared with controls (8.3 and 53.8% attached respectively, P < 0.001). The sperm-zona pellucida interaction described in this paper is applied as a functional assay for molecular interactions of sperm binding and can be used to assess function for potential surface markers on gametes. It is shown here that a unique binding ligand (PPS2) can be synthesized from another complimentary ligand (PPS1) without the need for a known intermediate substrate. PPS1 and PPS2 may have properties that can be used to target processes involved in conception and assisted reproduction. A movie sequence taken approximately 30 min after injection of spermatozoa into empty human zonae pellucidae shows behaviour of non-manipulated spermatozoa into zonae not exposed or exposed to ligand. This may be purchased for viewing on the Internet at www.rbmonline.com/Article/2159 (free to web subscribers).