THE ABALONE EGG VITELLINE ENVELOPE RECEPTOR FOR SPERM LYSIN IS A GIANT MULTIVALENT MOLECULE

Abalone sperm lysin is a 16-kDa acrosomal protein, which nonenzymatica lly and species selectively creates a hole in the egg vitelline envelo pe (VE) through which the sperm passes to reach the egg cell membrane. The crystal structures of both monomeric and dimeric lysins have been solved and the sequences of lysins from 20 abalone species have been determined, As a first step in understanding the molecular mechanism b y which lysin creates a hole in the VE, its VE receptor was isolated, The VE receptor for lysin (VERL) is an unbranched, rod-like molecule w ith an approximate relative molecular mass of 2 million; half the mass being carbohydrate. Fluorescence polarization studies showed positive cooperativity in the binding of lysin to VERL (EC50 approximate to 9 nM) and were consistent with tile species selectivity of lysin in diss olving VEs, Each molecule of VERL bound between 126 and 142 molecules of monomeric lysin (two independent assays), showing that VERL possess es repetitive lysin-binding motifs.