Biochemical analysis of the interaction of calcium with toposome: a major protein component of the sea urchin egg and embryo.
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.
Hayley
Michael
M
Department of Biochemistry, Memorial University of Newfoundland, St John's, Newfoundland, Canada A1B 3X9.
Sun
Ming
M
Merschrod
Erika F
EF
Davis
Philip J
PJ
Robinson
John J
JJ
D000818:Animals; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002413:Cations, Divalent / Q000737:chemistry / Q000378:metabolism; D004527:Egg Proteins / Q000737:chemistry* / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000737:chemistry* / Q000378:metabolism; D006023:Glycoproteins / Q000737:chemistry* / Q000378:metabolism; D008670:Metals / Q000737:chemistry / Q000378:metabolism; D018625:Microscopy, Atomic Force; D010063:Ovum / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D047270:Strongylocentrotus purpuratus / Q000737:chemistry* / Q000378:metabolism