cpTatC

cpTatC is a membrane protein component of the chloroplast twin-arginine translocation (Tat) system, a pathway that transports fully folded proteins across the thylakoid membrane into the thylakoid lumen. It is the chloroplast homolog of bacterial TatC and is found in plants and algae with plastids.

cpTatC is an integral, multi-pass membrane protein of roughly 240–300 amino acids that typically contains six transmembrane helices and cytosolic and lumenal loops. Together with the TatB-like protein Hcf106, cpTatC forms the high-affinity receptor complex that recognizes signal peptides bearing the conserved twin-arginine (RR) motif. Recognition of substrate and assembly of the translocase recruits Tha4 (a TatA family protein), which oligomerizes to form the translocation pore or facilitate membrane alterations that permit passage; the process is driven by the thylakoid proton motive force rather than ATP hydrolysis.

Functional studies in model plants show that loss or mutation of cpTatC impairs transport of native Tat substrates, leading to accumulation of precursor proteins, disrupted thylakoid protein composition, and defects in photosynthetic function. Structural and biochemical analyses of bacterial TatC and TatBC complexes provide a model for cpTatC architecture and signal peptide binding, although some plant-specific features and regulatory interactions remain under investigation. cpTatC is essential for proper thylakoid protein targeting and chloroplast biogenesis.