Tatpathway

Tatpathway, or twin-arginine translocation pathway, is a protein export system found in many bacteria, and in the chloroplasts of plants and some archaea. It uniquely transports fully folded proteins across the cytoplasmic membrane, unlike the Sec pathway, which generally translocates unfolded polypeptides.

In bacteria the machinery comprises TatA, TatB, and TatC. TatC serves as the initial receptor that recognizes signal peptides bearing a twin-arginine motif RR, typically within a consensus sequence such as SRRxFLK. The signal peptide is N-terminal and contains a twin-arginine pair followed by a hydrophobic region. TatA and TatB are smaller membrane proteins that assemble with TatC to form the translocation complex, with TatA thought to participate in forming or enlarging the translocation pore during transport.

Translocation is energized by the proton motive force across the inner membrane; ATP is not required. The exact mechanism remains a subject of study, but a common view is that TatC binds the substrate, TatA oligomerizes to create a transient channel, and the folded cargo moves into the periplasm or thylakoid lumen while cofactors are preserved.

Substrates include a range of periplasmic and membrane-associated enzymes, many of which carry cofactors or metal clusters, such as redox enzymes, hydrolases, and cytochromes. Not all secreted proteins use Tat; some rely on the Sec pathway or other export routes. In plants, chloroplast thylakoids host cpTat components (cpTatA, cpTatB, cpTatC) that export folded proteins into the lumen, contributing to photosynthetic function. The Tat pathway is a target of interest for biotechnology and antimicrobial research.