title: Biochemical analysis of the interaction of calcium with toposome: a major protein component of the sea urchin egg and embryo.
abstract: 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.
authors.affiliation: Department of Biochemistry, Memorial University of Newfoundland, St John's, Newfoundland, Canada A1B 3X9.
authors.forename: Michael
authors.initials: M
authors.lastname: Hayley
authors.forename: Ming
authors.initials: M
authors.lastname: Sun
authors.forename: Erika F
authors.initials: EF
authors.lastname: Merschrod
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Davis
authors.forename: John J
authors.initials: JJ
authors.lastname: Robinson
mesh_terms: 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