A POTENTIAL FUSION PEPTIDE AND AN INTEGRIN LIGAND DOMAIN IN A PROTEIN ACTIVE IN SPERM-EGG FUSION

THE union of sperm and egg is a special membrane fusion event that gives a signal 1 to begin development. We have hypothesized 2 that proteins mediating cell-cell fusion events resemble viral fusion proteins 3,4 and have shown that PH-30, a sperm surface protein involved in sperm-egg fusion 5, shares biochemical characteristics with viral fusion proteins 6. We report here the complementary DNA and deduced amino-acid sequences of the mature alpha and beta-subunits of PH-30. Both are type-I integral membrane glycoproteins. The alpha-subunit contains a putative fusion peptide typical of viral fusion proteins and the beta-subunit contains a domain related to a family of soluble integrin ligands found in snake venoms. Thus, the PH-30 alpha/beta complex resembles many viral fusion proteins in both its membrane topology and its predicted binding and fusion functions.