Calcium-binding proteins from the outer acrosomal membrane of ram spermatozoa: potential candidates for involvement in the acrosome reaction

Sukardi, S. and Elliott, R. M. and Withers, J. O. and Fontaine, U. and Millar, J. D. and Curry, M. R. and Watson, P. F. (2001) Calcium-binding proteins from the outer acrosomal membrane of ram spermatozoa: potential candidates for involvement in the acrosome reaction. Reproduction: Journal of the Society for Reproduction and Fertility, 122 (6). pp. 939-946. ISSN 1741-7899

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Official URL: http://dx.doi.org/10.1530/rep.0.1220939

Abstract

After an intracellular calcium influx, fusion of the sperm plasma membrane and outer acrosomal membrane (the acrosome reaction) precedes mammalian fertilization in vivo. This study describes the isolation of outer acrosomal membrane from ram spermatozoa and the subsequent characterization of calcium-binding proteins. Pooled ejaculates were diluted, cooled slowly and washed. Incubation with Hyamine 1622 (benzethenium chloride) and subsequent slow centrifugation gently dislodged and concentrated acrosomal membranes, the fragments of which were isolated on a two-step discontinuous sucrose gradient. The acrosomal membrane material stained with Giemsa, whereas spermatozoa from the gradient pellet stained intensely only in the equatorial segment. The acrosomal fraction showed a limited number of polypeptides by SDS-PAGE. Incubation with 45Ca2+ revealed two radioactive bands at 34 and 39 kDa. Extraction in the presence of EGTA implied that these proteins are not peripheral proteins associated with the membrane only in the presence of calcium ions, but are integral membrane proteins. Polyclonal antisera raised to the two bands showed specific binding to the anterior acrosomal region and demonstrated the intracellular location of the proteins. Sequence data of protein A revealed 83% homology with calnexin homologue precursor and 70% homology with annexin XI. Protein B showed 68% homology with protein SP-10 precursor and 64-72% homology with various annexins. However, crossreactivity with a range of commercial annexin antibodies and a specific antibody to a synthetic motif encompassing the annexin calcium-binding site was not demonstrable. It is concluded that the isolated proteins are unlikely to be annexins, but are possibly novel calcium-binding proteins

Item Type:Article
Additional Information:After an intracellular calcium influx, fusion of the sperm plasma membrane and outer acrosomal membrane (the acrosome reaction) precedes mammalian fertilization in vivo. This study describes the isolation of outer acrosomal membrane from ram spermatozoa and the subsequent characterization of calcium-binding proteins. Pooled ejaculates were diluted, cooled slowly and washed. Incubation with Hyamine 1622 (benzethenium chloride) and subsequent slow centrifugation gently dislodged and concentrated acrosomal membranes, the fragments of which were isolated on a two-step discontinuous sucrose gradient. The acrosomal membrane material stained with Giemsa, whereas spermatozoa from the gradient pellet stained intensely only in the equatorial segment. The acrosomal fraction showed a limited number of polypeptides by SDS-PAGE. Incubation with 45Ca2+ revealed two radioactive bands at 34 and 39 kDa. Extraction in the presence of EGTA implied that these proteins are not peripheral proteins associated with the membrane only in the presence of calcium ions, but are integral membrane proteins. Polyclonal antisera raised to the two bands showed specific binding to the anterior acrosomal region and demonstrated the intracellular location of the proteins. Sequence data of protein A revealed 83% homology with calnexin homologue precursor and 70% homology with annexin XI. Protein B showed 68% homology with protein SP-10 precursor and 64-72% homology with various annexins. However, crossreactivity with a range of commercial annexin antibodies and a specific antibody to a synthetic motif encompassing the annexin calcium-binding site was not demonstrable. It is concluded that the isolated proteins are unlikely to be annexins, but are possibly novel calcium-binding proteins
Keywords:Acrosome reaction, Calcium-binding proteins, Ram spermatozoa
Subjects:C Biological Sciences > C142 Reproductive Biology
C Biological Sciences > C131 Applied Cell Biology
D Veterinary Sciences, Agriculture and related subjects > D710 Agricultural Biology
Divisions:College of Science > School of Life Sciences
ID Code:906
Deposited By: Bev Jones
Deposited On:28 Jun 2007
Last Modified:18 Jul 2011 16:14

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