Structure and function of asterosaps, sperm-activating peptides from the jelly coat of starfish eggs

摘要

Animal eggs are generally encased in extracellular investments. These structures are not simply protective coats but play crucial roles in efficient fertilization. Sperm-activating peptide (SAP) is one of the bioactive components of the egg jelly coatin echinoderms (Garbers, 1989). SAP has several effects on spermatozoa such as stimulation of respiration and motility in the slightly acidified sea water, and an increase in intracellular pH and intracellular concentrations of Ca~(2+), cGMP and cAMP. Originally, the physiological roles of SAP were attributed only to maintaining sperm motility in the jelly coat (Suzuki et al., 1981). On the contrary, SAP is now considered to be a multi-functional peptide, namely chemoattraction (Ward et al., 1985; Miller & Vogt, 1996) and promotion of the acrosome reaction (Matsui et al. 1986; Yamaguchi et al. 1987).