The Tat Protein Export Pathway

Abstract

The Tat (twin arginine translocation) system is a recently discovered protein transport pathway which is found in the cytoplasmic membranes of many bacteria, and in the energy-transducing membranes of plant organelles. Proteins are targeted to the Tat export machinery by N-terminal signal peptides harbouring a distinctive ‘twin arginine’ motif. The Tat system serves to export a subset of periplasmic and periplasmic-facing proteins that normally require redox cofactors for activity. Overwhelming evidence suggests that substrate proteins are translocated across the membrane in a folded conformation, with their redox cofactors already bound, and in some cases as hetero-oligomers. This remarkable translocase is the first example of a protein transport system transporting folded substrates across an energy-coupling membrane. Here, the salient features of the bacterial Tat protein export pathway are discussed.