A Sperm Membrane Protein That Binds in a Species-specific Manner to the Egg Extracellular Matrix Is Homologous to von Willebrand Factor

Daniel M Hardy,David L Garbers

doi:10.1074/jbc.270.44.26025

Daniel M Hardy, David L Garbers

Open Access

https://doi.org/10.1074/jbc.270.44.26025

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Abstract

We have purified a sperm membrane protein, designated zonadhesin, that binds in a species-specific manner to the extracellular matrix (zona pellucida) of the egg, and cloned its cDNA. The cDNA encodes a novel protein with a single transmembrane segment separating a 36 amino acid, highly basic intracellular C terminus from a 2418-amino acid extracellular region. The extracellular sequence specifies a mosaic protein comprising a unique N-terminal domain, a mucin-like domain, and five tandem domains proximal to the membrane that are homologous to prepro von Willebrand factor. The N-terminal and mucin-like domains were absent from zonadhesin that bound to the egg extracellular matrix, suggesting that processing occurs during sperm maturation and/or capacitation. By Northern blotting and in situ hybridization, zonadhesin mRNA was detected only within the testis, where it was expressed primarily in haploid spermatids. The unique domain structure of zonadhesin suggests multiple functions, one of which is to mediate sperm adhesion to the zona pellucida.

Highlights

Fertilization in both invertebrates and vertebrates is species-specific, and events such as motility activation, gamete adhesion, and induction of the acrosome reaction show absolute or relative species specificity [1,2,3,4,5]
Zonadhesin was purified to apparent homogeneity based on its zona pellucida binding activity (Fig. 1)
30 ␮g of p105 and 10 –15 ␮g of p45 were obtained from 880 mg of sperm membrane protein, using 44 mg of native, particulate zona pellucida as the affinity matrix

Summary

Introduction

Fertilization in both invertebrates and vertebrates is species-specific, and events such as motility activation, gamete adhesion, and induction of the acrosome reaction show absolute or relative species specificity [1,2,3,4,5]. Sperm membrane proteins that interact with the egg in a species-specific manner are likely to be primary gamete recognition and/or signaling components. We have purified this sperm membrane protein (named zonadhesin), obtained partial amino acid sequence, and isolated its cDNA.

Results

Conclusion