title: The TatC component of the twin-arginine protein translocase functions as an obligate oligomer.
abstract: The Tat protein export system translocates folded proteins across the bacterial cytoplasmic membrane and the plant thylakoid membrane. The Tat system in Escherichia coli is composed of TatA, TatB and TatC proteins. TatB and TatC form an oligomeric, multivalent receptor complex that binds Tat substrates, while multiple protomers of TatA assemble at substrate-bound TatBC receptors to facilitate substrate transport. We have addressed whether oligomerisation of TatC is an absolute requirement for operation of the Tat pathway by screening for dominant negative alleles of tatC that inactivate Tat function in the presence of wild-type tatC. Single substitutions that confer dominant negative TatC activity were localised to the periplasmic cap region. The variant TatC proteins retained the ability to interact with TatB and with a Tat substrate but were unable to support the in vivo assembly of TatA complexes. Blue-native PAGE analysis showed that the variant TatC proteins produced smaller TatBC complexes than the wild-type TatC protein. The substitutions did not alter disulphide crosslinking to neighbouring TatC molecules from positions in the periplasmic cap but abolished a substrate-induced disulphide crosslink in transmembrane helix 5 of TatC. Our findings show that TatC functions as an obligate oligomer.
authors.affiliation: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.
authors.forename: François
authors.initials: F
authors.lastname: Cléon
authors.affiliation: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.
authors.forename: Johann
authors.initials: J
authors.lastname: Habersetzer
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK.
authors.forename: Felicity
authors.initials: F
authors.lastname: Alcock
authors.affiliation: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.
authors.forename: Holger
authors.initials: H
authors.lastname: Kneuper
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK.
authors.forename: Phillip J
authors.initials: PJ
authors.lastname: Stansfeld
authors.affiliation: Department of Chemistry, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK.
authors.forename: Hajra
authors.initials: H
authors.lastname: Basit
authors.affiliation: Department of Chemistry, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK.
authors.forename: Mark I
authors.initials: MI
authors.lastname: Wallace
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, UK.
authors.forename: Ben C
authors.initials: BC
authors.lastname: Berks
authors.affiliation: Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.
authors.forename: Tracy
authors.initials: T
authors.lastname: Palmer
mesh_terms: D000595:Amino Acid Sequence; D001120:Arginine; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D019897:Periplasm / Q000378:metabolism; D010641:Phenotype; D011485:Protein Binding; D021122:Protein Subunits; D021381:Protein Transport
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D021122:Protein Subunits; C461379:TatC protein, E coli; D001120:Arginine