title: The superoxide dismutase SodA is targeted to the periplasm in a SecA-dependent manner by a novel mechanism.
abstract: The manganese/iron-type superoxide dismutase (SodA) of Rhizobium leguminosarum bv. viciae 3841 is exported to the periplasm of R. l. bv. viciae and Escherichia coli. However, it does not possess a hydrophobic cleaved N-terminal signal peptide typically present in soluble proteins exported by the Sec-dependent (Sec) pathway or the twin-arginine translocation (TAT) pathway. A tatC mutant of R. l. bv. viciae exported SodA to the periplasm, ruling out export of SodA as a complex with a TAT substrate as a chaperone. The export of SodA was unaffected in a secB mutant of E. coli, but its export from R. l. bv. viciae was inhibited by azide, an inhibitor of SecA ATPase activity. A temperature-sensitive secA mutant of E. coli was strongly reduced for SodA export. The 10 N-terminal amino acid residues of SodA were sufficient to target the reporter protein alkaline phosphatase to the periplasm. Our results demonstrate the export of a protein lacking a classical signal peptide to the periplasm by a SecA-dependent, but SecB-independent targeting mechanism. Export of the R. l. bv. viciae SodA to the periplasm was not limited to the genus Rhizobium, but was also observed in other proteobacteria.
authors.affiliation: Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich NR47UH, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Krehenbrink
authors.forename: Anne
authors.initials: A
authors.lastname: Edwards
authors.forename: J Allan
authors.initials: JA
authors.lastname: Downie
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D019897:Periplasm / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D021381:Protein Transport; D016961:Rhizobium leguminosarum / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C057842:SecB protein, Bacteria; C095500:SodA protein, Bacteria; D013482:Superoxide Dismutase; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins