title: Purification and N-terminal sequence of the alpha subunit of antigen 43, a unique protein complex associated with the outer membrane of Escherichia coli.
abstract: Antigen 43 has been identified as a unique protein complex in the outer membrane of Escherichia coli. The complex contains two different polypeptides, alpha (Mr, 60,000) and beta (Mr, 53,000), in equal stoichiometry (P. Owen, P. Caffrey, and L.-G. Josefsson, J. Bacteriol. 169:3770-3777, 1987). The alpha subunit was released in a water-soluble form upon heating of outer membranes to 60 degrees C and was purified to apparent homogeneity by gel filtration and ion-exchange chromatography. The purified protein was acidic (pI 4.6) and had a polarity of 49.2%. The N-terminal sequence showed homology with the N termini of certain enterobacterial fimbrial subunits. In addition, antigen 43 underwent a reversible phase variation similar to that of type 1 fimbriae. By use of subunit-specific antisera, it was shown that the purified alpha subunit was capable of reassociating with the beta polypeptide. However, electron microscopic examination indicated that antigen 43 does not form a recognizable surface structure. The available evidence supports the view that antigen 43 is a complex consisting of a peripheral membrane protein (alpha) anchored to a subunit (beta) that is integral to the outer membrane.
authors.affiliation: Department of Microbiology, Trinity College, Dublin, Ireland.
authors.forename: P
authors.initials: P
authors.lastname: Caffrey
authors.forename: P
authors.initials: P
authors.lastname: Owen
mesh_terms: D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000235:genetics / Q000302:isolation & purification*; D000954:Antigens, Surface / Q000235:genetics / Q000302:isolation & purification; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000302:isolation & purification*; D003378:Counterimmunoelectrophoresis; D004926:Escherichia coli / Q000276:immunology* / Q000648:ultrastructure; D006358:Hot Temperature; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011233:Precipitin Tests; D011487:Protein Conformation; D012689:Sequence Homology, Nucleic Acid
chemical_list: D000942:Antigens, Bacterial; D000954:Antigens, Surface; D001425:Bacterial Outer Membrane Proteins