cpTatA

cpTatA is a component of the chloroplast twin-arginine translocation (Tat) pathway, a protein export system in the thylakoid membranes of chloroplasts. It works together with cpTatB and cpTatC to form the Tat translocase that transports fully folded proteins across the thylakoid membrane, typically into the lumen.

The cpTatA protein is small and hydrophobic, featuring a single N-terminal transmembrane helix followed by an amphipathic region. In plants and algae, cpTatA is encoded in the nuclear genome and is synthesized with a chloroplast transit peptide that targets it to the organelle; the transit peptide is cleaved to yield the mature cpTatA that anchors in the thylakoid membrane.

In the translocase, cpTatA is believed to participate in pore formation and substrate translocation, assembling into oligomeric complexes with cpTatB and cpTatC. It is part of a mechanistic model in which cpTatA contributes to gating and passage of substrates bearing twin-arginine signal peptides (RR) as they are moved across the membrane, driven by the proton motive force.

Evolutionarily, cpTatA represents the chloroplast counterpart of bacterial TatA and shares functional and structural similarities. The cpTatA and cpTatB components are typically nuclear-encoded in plants and algae, reflecting the endosymbiotic origin of chloroplasts and the retention of a Tat system adapted to the chloroplast environment.

See also: Twin-arginine translocation pathway, cpTatB, cpTatC.