title: The structure and associations of the double S layer on the cell wall of Aquaspirillum sinuosum.
abstract: Aquaspirillum sinuosum cell walls bear two paracrystalline, proteinaceous surface layers (S layers). Each shows a different symmetry: the inner layer is closely apposed to the outer membrane and is a tetragonal array (90 degrees axes; 5-nm units; repeat frequency 8 nm); the outer layer is a hexagonal array on the external surface (14-nm units; repeat frequency 18 nm) and, although the units have a six-pointed stellate form, the linkage between units is not resolved. The outer layer consists of a major 130-kDa protein and a 180-kDa minor component; these co-extract, co-assemble, and are inseparable by hydroxylapatite chromatography or by recrystallization. The solubilizing effects of reagents suggest stabilization by hydrogen bonding and Ca2+. The two outer layer proteins are serologically related and show partial identity by peptide mapping. Periodic acid--Schiff staining of the 180-kDa band suggests that this may be a glycosylated form of the 130-kDa component. The inner layer components form a doublet of 75- and 80-kDa polypeptides with extreme resistance to extraction. Close apposition to the outer membrane, resistance to chaotropes, aqueous insolubility, and behaviour in charge-shift electrophoresis suggest hydrophobic interaction between subunits and an integral association with the outer membrane.
authors.affiliation: Department of Microbiology and Immunology, University of Western Ontario, London, Canada.
authors.forename: S H
authors.initials: SH
authors.lastname: Smith
authors.forename: R G
authors.initials: RG
authors.lastname: Murray
mesh_terms: D000942:Antigens, Bacterial; D001419:Bacteria / Q000032:analysis / Q000276:immunology / Q000648:ultrastructure*; D001425:Bacterial Outer Membrane Proteins / Q000276:immunology / Q000302:isolation & purification; D002473:Cell Wall / Q000032:analysis / Q000276:immunology / Q000648:ultrastructure; D008854:Microscopy, Electron; D008970:Molecular Weight
chemical_list: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins