Acrosomal proteins

The abalone sperm AR can be artificially induced by raising the calcium ion concentration of seawater from the normal 10 mM to 50 mM in seawater buffered with 10 mM Tris at pH 8.2. Unlike other species used for fertilization studies, the abalone AR does not lead to the rapid death of the sperm. In abalone sperm, the acrosomal compartment is sealed off from the respiratory compartment acrosome-reacted, sperm will continue to swim for days if stored in the cold room at 4°C. The acrosomal exudate of these sperm is composed predominantly of soluble ly sin and 18K protein. Reducing and denaturing polyacrylamide gel electrophoresis of whole sperm, AV exudate, and purified lysin shows that abalone spermatocytes make a substantial investment in the synthesis of these two acrosomal proteins (Figure 6). 

Primers were made to obtain the full length sequences of five species by PCR (Swanson and Vacquier, 1995b). Instead of presenting an alignment of all 27 lysin sequences and the five 18K sequences, we will present the sequences of both proteins from five species of California abalone (Figure 9 Vacquier et al., 1997). The sequences of both acrosomal proteins are known for four species. Haliotis kamtschatkana (known for lysin) and H. assimilis (known for 18K) are considered to be comparable, closely related species. 

Table 1. Pairwise Comparisons of the Percent Identity of the Mature Acrosomal Proteins, Number of Synonymous (Ds), and Nonsynonymous (Dn) Substitutions Per...

Usui, N. and Haino-Fukushima, K. (1991). Two major acrosomal proteins act on different parts of the oocyte vitelline coat in the abalone Haliolis discus. Mol. Reprod. and Dev. 28 189-198. 

Sperm penetrate the zona pellucida only after completion of the acrosome reaction. A similar process occurs in nonmammalian species, where sperm must penetrate the vitelline coat. In abalone this is accomplished by release of lysin, an acrosomal protein that disperses the vitelline coat by a noncatalytic mechanism (Lewis et al., 1982 Shaw et al., 1993). In contrast, the generally accepted model for mammalian sperm penetration of the zona pellucida is the acrosin hypothesis in which proteolysis of zona pellucida matrix glycoproteins by acrosin, the acrosomal serine esterase, plays a trailblazing role in the sperm penetration process (Yanag-... 

Yamagata, K., Murayama, K., Okabe, M., Toshimori, K., Nakanishi, T., Kashiwabara, S., and Baba, T. (1998). Acrosin accelerates the dispersal of sperm acrosomal proteins during acrosome reaction. J. Biol. Chem. 273 10470-10474. 

In Chapter 2, Vacquier and coauthors present a detailed account of their research on two acrosomal proteins of abalone sperm. This research has significantly advanced our understanding of how species-specificity evolves. Knowledge of the behavior and structure of these sperm proteins has suggested possible mechanisms of evolution of species-specific gamete interactions and has demonstrated that these proteins may play essential roles in establishing reproductive isolation between species. 

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