title: Membrane topology of the chromate transporter ChrA of Pseudomonas aeruginosa.
abstract: The membrane topology of the plasmid-encoded Pseudomonas aeruginosa ChrA protein, which effluxes chromate ions, was determined by the analysis of translational fusions with reporter enzymes alkaline phosphatase and beta-galactosidase. A novel 13-TMS (transmembrane segments) topology, with the N-terminus located in the cytoplasm and the C-terminus in the periplasmic space, was consistent with the enzyme activities determined in both Escherichia coli and P. aeruginosa. Alignment of the two halves of ChrA showed significant sequence homology, with TMS I, II, III, IV, V and VI displaying similarity to TMS VIII, IX, X, XI, XII and XIII, respectively, although with opposite membrane orientations. This suggests that ChrA arose from the duplication of a gene encoding a 6-TMS ancestral protein, followed by the insertion of extra TMS VII. These data also suggest that the two halves of ChrA may carry out distinct functions for the transport of chromate.
authors.affiliation: Instituto de Investigaciones Químico-Biológicas, Universidad Michoacana, Morelia, Mich., México.
authors.forename: Rafael
authors.initials: R
authors.lastname: Jiménez-Mejía
authors.forename: Jesús
authors.initials: J
authors.lastname: Campos-García
authors.forename: Carlos
authors.initials: C
authors.lastname: Cervantes
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics*; D002840:Chromates / Q000378:metabolism* / Q000494:pharmacology; D020440:Gene Duplication; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics*; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010957:Plasmids; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D002840:Chromates; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011993:Recombinant Fusion Proteins; C073039:ChrA protein, Bacteria