Genetic Evidence for a Tight Cooperation of TatB and TatC during Productive Recognition of Twin-Arginine

• Published in: PloS one 2012-06, Vol.7 (6), p.e39867
• Main Authors: Lausberg, Frank, Fleckenstein, Stefan, Kreutzenbeck, Peter, Fröbel, Julia, Rose, Patrick, Müller, Matthias, Freudl, Roland
• Format: Article
• Language: English
• Subjects: Amino acids; Analysis; Escherichia coli; International trade; Protein binding; Proteins
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0039867

The twin arginine translocation (Tat) pathway transports folded proteins across the cytoplasmic membrane of bacteria. Tat signal peptides contain a consensus motif (S/T-R-R-X-F-L-K) that is thought to play a crucial role in substrate recognition by the Tat translocase. Replacement of the phenylalanine at the +2 consensus position in the signal peptide of a Tat-specific reporter protein (TorA-MalE) by aspartate blocked export of the corresponding TorA(D.sup.+2 )-MalE precursor, indicating that this mutation prevents a productive binding of the TorA(D.sup.+2) signal peptide to the Tat translocase. Mutations were identified in the extreme amino-terminal regions of TatB and TatC that synergistically suppressed the export defect of TorA(D.sup.+2 )-MalE when present in pairwise or triple combinations. The observed synergistic suppression activities were even more pronounced in the restoration of membrane translocation of another export-defective precursor, TorA(KQ)-MalE, in which the conserved twin arginine residues had been replaced by lysine-glutamine. Collectively, these findings indicate that the extreme amino-terminal regions of TatB and TatC cooperate tightly during recognition and productive binding of Tat-dependent precursor proteins and, furthermore, that TatB and TatC are both involved in the formation of a specific signal peptide binding site that reaches out as far as the end of the TatB transmembrane segment.