title: Crystallization of p68 on lipid monolayers and as three-dimensional single crystals.
abstract: 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.
authors.affiliation: Imperial Cancer Research Fund Laboratories, London, U.K.
authors.forename: R
authors.initials: R
authors.lastname: Newman
authors.forename: A
authors.initials: A
authors.lastname: Tucker
authors.forename: C
authors.initials: C
authors.lastname: Ferguson
authors.forename: D
authors.initials: D
authors.lastname: Tsernoglou
authors.forename: K
authors.initials: K
authors.lastname: Leonard
authors.forename: M J
authors.initials: MJ
authors.lastname: Crumpton
mesh_terms: D017317:Annexin A6; D002135:Calcium-Binding Proteins / Q000378:metabolism; D003460:Crystallization; D006801:Humans; D010743:Phospholipids / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D017317:Annexin A6; D002135:Calcium-Binding Proteins; D010743:Phospholipids