Mode of action of sperm-activating peptide

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In the past decade, we purified 74 sperm-activating peptides from the egg jelly of 17 species of sea urchins distributed over five taxonomic orders. These peptides show essentially the same biological effects on sea urchin spermatozoa although the biological effects and structures of the peptides are specific at the ordinal level. With regard to that specificity, these peptides can be classified into five groups. Sperm-activating peptide I (SAP-I : GFDLNGGGVG) crosslinked specifically to a 71 kDa protein and induced an electrophoretic mobility change in the guanylate cyclase of Hemicentrotus pulcherrimus sperm plasma membrane with concomitant dephosphorylation and inactivation of the enzyme. The dephosphorylation and subsequent inactivation of the enzyme were inhibited in the presence of calyculin A. The phosphorylated and dephosphorylated forms of the guanylate cyclase contained about 24 and 4 moles of phosphate per mol protein, respectively. A cDNA clone for the gudnylate cyclase has been isolated from a cDNA library for H. pulcherrimus testes. An open reading frame predicted a protein of 1125 amino acids including an apparent signal peptide of 21 residues ; a single transmembrane domain of 25 amino acids divided the mature protein into an amino-terminal, extracellular domain of 485 amino acids and carboxyl domain of 594 intracellular amino acids. The intracellular domain possessed a kinase-like region and a catalytic region. Nine and fifteen serine residues existed in the kinase-like and the catalytic regions, respectively. We purified three different protein phosphatases from the sperm tails. The activity of these enzyme was inhibited by calyculin A.