Contributions of the transmembrane domain and a key acidic motif to assembly and function of the TatA complex.
The twin-arginine translocase (Tat) pathway transports folded proteins across bacterial and thylakoid membranes. In Escherichia coli, a membrane-bound TatA complex, which oligomerizes to form complexes of less than 100 to more than 500 kDa, is considered essential for translocation. We have studied the contributions of various TatA domains to the assembly and function of this heterogeneous TatA complex. The TOXCAT assay was used to analyze the potential contribution of the TatA transmembrane (TM) domain. We observed relatively weak interactions between TatA TM domains, suggesting that the TM domain is not the sole driving force behind oligomerization. A potential hydrogen-bonding role for a TM domain glutamine was also investigated, and it was found that mutation blocks transport at low expression levels, while assembly is unaffected at higher expression levels. Analysis of truncated TatA proteins instead highlighted an acidic motif directly following the TatA amphipathic helix. Mutating these negatively charged residues to apolar uncharged residues completely blocks activity, even at high levels of TatA, and appears to disrupt ordered complex formation.
Warren
Gemma
G
MOAC Doctoral Training Centre, University of Warwick, Coventry CV4 7AL, UK.
Oates
Joanne
J
Robinson
Colin
C
Dixon
Ann M
AM
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry*; D026901:Membrane Transport Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D020524:Thylakoids / Q000378:metabolism
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; C499697:TatA protein, E coli