title: Isolation and cloning of Omp alpha, a coiled-coil protein spanning the periplasmic space of the ancestral eubacterium Thermotoga maritima.
abstract: We have discovered a new oligomeric protein component associated with the outer membrane of the ancestral eubacterium Thermotoga maritima. In electron micrographs, the protein, Omp alpha, appears as a rod-shaped spacer that spans the periplasm, connecting the outer membrane to the inner cell body. Purification, biochemical characterization and sequencing of Omp alpha suggest that it is a homodimer composed of two subunits of 380 amino acids with a calculated M(r) of 43,000 and a pI of 4.54. The sequence of the omp alpha gene indicates a tripartite organization of the protein with a globular NH2-terminal domain of 64 residues followed by a putative coiled-coil segment of 300 residues and a COOH-terminal, membrane-spanning segment. The predicted length of the coiled-coil segment (45 nm) correlates closely with the spacing between the inner and outer membranes. Despite sequence similarity to a large number of coiled-coil proteins and high scores in a coiled-coil prediction algorithm, the sequence of the central rod-shaped domain of Omp alpha does not have the typical 3.5 periodicity of coiled-coil proteins but rather has a periodicity of 3.58 residues. Such a periodicity was also found in the central domain of staphylococcal M protein and beta-giardin and might be indicative of a subclass of fibrous proteins with packing interactions that are distinct from the ones seen in other two-stranded coiled-coils.
authors.affiliation: Max-Planck-Institut für Biochemie, Martinsried, Germany.
authors.forename: A M
authors.initials: AM
authors.lastname: Engel
authors.forename: Z
authors.initials: Z
authors.lastname: Cejka
authors.forename: A
authors.initials: A
authors.lastname: Lupas
authors.forename: F
authors.initials: F
authors.lastname: Lottspeich
authors.forename: W
authors.initials: W
authors.lastname: Baumeister
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000648:ultrastructure; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D004591:Electrophoresis, Polyacrylamide Gel; D005614:Freeze Fracturing; D006089:Gram-Negative Anaerobic Bacteria / Q000737:chemistry / Q000235:genetics* / Q000648:ultrastructure; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D018272:Porins; D017433:Protein Structure, Secondary
chemical_list: D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; D018272:Porins; C078167:OMPA outer membrane proteins