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Biochemical analysis of the interaction of calcium with toposome: a major protein component of the sea urchin egg and embryo.

Hayley M, Sun M, Merschrod EF, Davis PJ, Robinson JJ

Department of Biochemistry, Memorial University of Newfoundland, St John's, Newfoundland, Canada A1B 3X9.

We have investigated the biochemical and functional properties of toposome, a major protein component of sea urchin eggs and embryos. Atomic force microscopy was utilized to demonstrate that a Ca(2+)-driven change in secondary structure facilitated toposome binding to a lipid bilayer. Thermal denaturation studies showed that toposome was dependent upon calcium in a manner paralleling the effect of this cation on secondary and tertiary structure. The calcium-induced, secondary, and tertiary structural changes had no effect on the chymotryptic cleavage pattern. However, the digestion pattern of toposome bound to phosphatidyl serine liposomes did vary as a function of calcium concentration. We also investigated the interaction of this protein with various metal ions. Calcium, Mg(2+), Ba(2+), Cd(2+), Mn(2+), and Fe(3+) all bound to toposome. In addition, Cd(2+) and Mn(2+) displaced Ca(2+), prebound to toposome, while Mg(2+), Ba(2+), and Fe(3+) had no effect. Collectively, these results further enhance our understanding of the role of Ca(2+) in modulating the biological activity of toposome.

Published 2 April 2008 in J Cell Biochem, 103(5): 1464-71.
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