STRUCTURE AND FUNCTION OF ASTEROSAPS, SPERM-ACTIVATING PEPTIDES FROM THE JELLY COAT OF STARFISH EGGS

Jelly coat of starfish eggs has the capacity to activate homologous sp ermatozoa and induce the acrosome reaction. We have isolated 12 sperm- activating peptides (SAPs) from the egg jelly of the starfish, Asteria s amurensis. Eleven SAPs were structurally identified by sequence anal ysis and electrospray ionisation mass spectrometry. All of them are gl utamine-rich tetratriacontapeptides with an intramolecular disulphide Linkage between Cys(8) and Cys(32). They are much larger than sea urch in SAPs and do not show any significant sequence similarities to known proteins. Thus we have collectively named them asterosaps. The amino terminal region, where structural diversity of asterosaps is observed, is not important for their activity, whereas the disulphide Linkage i s essential. Asterosaps do not induce the acrosome reaction by themsel ves, but are able to induce the acrosome reaction in combination with an egg jelly glycoconjugate named ARTS. Furthermore, anti-asterosap ra bbit antibody significantly decreased the acrosome reaction-inducing a ctivity of the jelly solution and the activity was restored by additio n of excess asterosap. These results support our hypothesis that the m ain physiological role of SAPs is the induction of the acrosome reacti on in cooperation with two other jelly components, ARTS and Co-ARIS.