Redundancy and specificity of multiple Trigger Factor chaperones in Desulfitobacteria

The ribosome-bound Trigger Factor (TF) chaperone assists folding of newly synthesized polypeptides and participates in the assembly of macromolecular complexes. In the present study we showed that multiple distinct TF paralogues are present in genomes of Desulfitobacteria, a bacterial genus known for its ability to grow upon organohalide respiration. Two full-length TF chaperones and at least one truncated TF (lacking the N-terminal ribosome-binding domain) were identified, the latter being systematically linked to clusters of reductive dehalogenase genes encoding the key enzymes in organohalide respiration. Using a well characterized heterologous chaperone-deficient E. coli strain lacking both TF and DnaK chaperones, we demonstrated that all three TF chaperones were functional in vivo, as judged by their ability to partially suppress bacterial growth defect and protein aggregation in the absence of both major E. coli chaperones. Next, we found that the N-terminal truncated TF-like protein PceT functions as a dedicated chaperone for the cognate reductive dehalogenase PceA by solubilizing and stabilizing it in the heterologous system. Finally we showed that PceT specifically interacts with the twin-arginine signal peptide of PceA. Taken together, our data defines PceT (and more generally the new RdhT family) as a class of TF-like chaperones involved in the maturation of proteins secreted by the Twin-arginine translocation pathway.