title: Expression of the bifunctional Bacillus subtilis TatAd protein in Escherichia coli reveals distinct TatA/B-family and TatB-specific domains.
abstract: In the Tat protein export pathway of Gram-negative bacteria, TatA and TatB are homologous proteins that carry out distinct and essential functions in separate sub-complexes. In contrast, Gram-positive Tat systems usually lack TatB and the TatA protein is bifunctional. We have used a mutagenesis approach to delineate TatA/B-type domains in the bifunctional TatAd protein from Bacillus subtilis. This involved expression of mutated TatAd variants in Escherichia coli and tests to determine whether the variants could function as TatA or TatB by complementing E. coli tatA and/or tatB mutants. We show that mutations in the C-terminal half of the transmembrane span and the subsequent FGP 'hinge' motif are critical for TatAd function with its partner TatCd subunit, and the same determinants are required for complementation of either tatA or tatB mutants in Escherichia coli. This is thus a critical domain in both TatA and TatB proteins. In contrast, substitution of a series of residues at the N-terminus specifically blocks the ability of TatAd to substitute for E. coli TatB. The results point to the presence of a universally conserved domain in the TatA/B-family, together with a separate N-terminal domain that is linked to the TatB-type function in Gram-negative bacteria.
authors.affiliation: School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK.
authors.forename: James P
authors.initials: JP
authors.lastname: Barnett
authors.forename: Janna
authors.initials: J
authors.lastname: Lawrence
authors.forename: Sharon
authors.initials: S
authors.lastname: Mendel
authors.forename: Colin
authors.initials: C
authors.lastname: Robinson
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001412:Bacillus subtilis / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005816:Genetic Complementation Test; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D054730:Protein Interaction Domains and Motifs; D021381:Protein Transport; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D026901:Membrane Transport Proteins