Amino acid sequence of an egg-lysin protein from abalone spermatozoa that solubilizes the vitelline layer

Spermatozoa of the California red abalone (Haliotis rufescens; Phylum Mollusca, order Archeogastropoda) possess an acrosomal protein that dissolves the egg vitelline layer during fertilization. Evidence strongly suggests that the dissolution mechanism is a stoichiometric, nonenzymatic process that depends on the hydrophobic nature of the sperm protein which should therefore be termed an egg-lysin. Here we report the complete amino acid sequence of this unique protein. Peptides obtained by cyanogen bromide cleavage and trypsin and V8 protease digestions were isolated and subjected to automated Edman degradation. Seven unique CNBr fragments accounted for the intact lysin and the proteolytically derived peptides were used to establish the order of these fragments. The protein is composed of 134 amino acids and contains 36 charged amino acids. The majority of these occur at distances of 2 or 3 residues from each other. A stretch of 41 amino acids contains 10 positively charged amino acids and no negatively charged residue. Model building experiments demonstrated that the charged residues that may occur in alpha-helical regions of the protein would occupy one-half of the circumference of such helices. The other half would display predominantly hydrophobic residues. This arrangement of the charged and hydrophobic residues may account for the biological properties of the lysin.