The process of fertilization is ubiquitous, yet the interactions between the sperm and the egg are one of the least studied areas of cellular, molecular, and structural biology. One question of interest in fertilization biology is the nature of species specific interactions between gametes. The abalone is an ideal organism in which to study this question. Abalone gametes are abundant and easy to obtain. Many abalone have overlapping environments and breeding seasons, yet hybrids are rare, indicating a mechanism that prevents cross-species fertilization. Inside the anterior tip of the abalone sperm is the acrosomal vesicle which contains two proteins - a 16 kDa protein named """"""""lysin"""""""" and an 18 kDa protein. Lysin dissolves the outer protective coat of the egg while the 18 kDa protein is involved in fusing the membranes of the male and female gametes. The two proteins are thought to have arisen via a gene duplication and have similar predicted secondary and tertiary structures. Primary sequence alignments of both proteins indicate regions of homology involved in function interspersed with regions of hyper-variable residues that participate in species-specific recognition. Lysin occurs as a dimer in solution and a monomer in its active form. The structures of both dimeric and monomeric lysin have been solved to 2.8 E and 1.9 E respectively. High resolution data collected at beamline 9-1 allowed us determine the structures to 2.0 E and 1.3 E respectively. We have also determined the 1.7 E structure of the lysin dimer from green abalone using native and derivative data collected at beamline 9-1. Athough full analysis of the structures has not yet been completed, the details learned from comparisons of these structures will aid in deducing the molecular nature of species-specific fertilization.
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