tatC

TatC is a membrane protein that serves as a central component of the twin-arginine translocation (Tat) pathway, found in many bacteria and in the chloroplasts of plants. It is an integral inner membrane protein that typically contains six predicted transmembrane helices and a large cytoplasmic or periplasmic loop that contributes to substrate recognition. In Escherichia coli and many other species, TatC is encoded together with TatA and TatB in a tatABC operon and forms a receptor complex for Tat substrates.

TatC recognizes the twin-arginine signal peptide of substrate proteins, which contains a consensus motif SRRxFLK near the N-terminus. Binding of the signal peptide to TatC, often in collaboration with TatB, recruits the folded cargo to the translocation machinery. Substrates translocate across the cytoplasmic membrane in a process powered by the proton motive force, with TatA oligomerization forming the translocation channel as needed. Unlike Sec pathways, Tat transports fully folded proteins and cofactor-containing complexes, such as periplasmic enzymes and Rieske-type proteins.

TatC is highly conserved and is essential for Tat pathway function in most organisms that possess it. Homologs are present in many Gram-negative and Gram-positive bacteria and in chloroplasts, where the pathway delivers proteins into the thylakoid lumen. Disruption of tatC generally abolishes Tat-dependent secretion, impacting cellular processes and, in some pathogens, virulence.