Crystallization of p68 on lipid monolayers and as three-dimensional single crystals.
Two-dimensional crystals of p68, a Ca2+ -binding protein that has homology with members of the lipocortin/calpactin family, were obtained by interaction with a phospholipid monolayer. By measuring surface pressure at constant surface area, p68 was found to interact in a Ca2+ -dependent manner specifically with phosphatidylethanolamine, less so with phosphatidylserine and not at all with phosphatidylcholine. With dimyristoyl-phosphatidylethanolamine, two-dimensional crystalline arrays were formed. Image analysis of electron micrographs of these crystals, which diffracted to about 50 A, revealed p3 symmetry with a unit cell of about 178 A by 178 A; the protein densities showed a two-domain structure giving a cylindrical molecule of about 100 A by 35 A diameter packed as trimers. Three-dimensional microcrystals obtained without lipid or Ca2+ were suitable for electron microscopy and gave a tetragonal unit cell of about 256 A by 68 A. The implications of these observations on the structure and lipid specificity of p68 binding are discussed.[1]References
- Crystallization of p68 on lipid monolayers and as three-dimensional single crystals. Newman, R., Tucker, A., Ferguson, C., Tsernoglou, D., Leonard, K., Crumpton, M.J. J. Mol. Biol. (1989) [Pubmed]
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