title: Two-dimensional crystals of cholera toxin B-subunit-receptor complexes: projected structure at 17-A resolution.
abstract: The B subunit of cholera toxin forms two-dimensional crystals when bound to its membrane receptor, ganglioside GM1, in phospholipid layers. A rectangular crystal lattice gives diffraction extending to 15-A resolution in negative stain, and image-processing of electron micrographs reveals a ring of five protein densities. The diameter of the central hole and the outer diameter of the ring are about 20 and 60 A, respectively. These data are consistent with a pentameric, doughnut-shaped structure of the B subunit that lies flat on a membrane surface. A hexagonal crystal lattice is obtained as well, and results of image processing and chemical crosslinking allow two interpretations: the B subunit may exist in both pentameric and hexameric forms or, more likely, the hexagonal lattice may represent a disordered or liquid crystalline form, in which a pentamer undergoes rotational averaging about its 5-fold axis.
authors.forename: D S
authors.initials: DS
authors.lastname: Ludwig
authors.forename: H O
authors.initials: HO
authors.lastname: Ribi
authors.forename: G K
authors.initials: GK
authors.lastname: Schoolnik
authors.forename: R D
authors.initials: RD
authors.lastname: Kornberg
mesh_terms: D002772:Cholera Toxin; D003460:Crystallization; D005677:G(M1) Ganglioside; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic
chemical_list: D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; C023552:choleragen receptor; D005677:G(M1) Ganglioside; D002772:Cholera Toxin