Twin-arginine translocation pathway
As a Twin - Arginine Translocation (English for twin -arginine transport), briefly indeed, Tat system in biochemistry a special transport system for proteins in plants, bacteria and archaea is called. This Proteintransportweg is used in the plant thylakoid membrane and in the plasma membrane of bacteria and archaea. It is one of the post-translational protein transport paths and allows, in contrast to Sec-dependent protein transport the transport of proteins in the folded state.
The Tat- dependent protein transport was first discovered in plants, where it was first described as ApH - dependent protein transport, since the proton gradient across the thylakoid membrane is used as an energy source for transportation. This dependence, however, is now controversial. In bacteria, the evolutionary precursors of chloroplasts (see endosymbiotic theory ) of the Tat pathway was found.
Far three membrane proteins have been identified that are essential for the transport. These are called TatA, TatB and TatC. Originally, the proteins in the plant system as THA4 ( TatA ) were Hcf106 ( TatB ) and cpTatC ( TatC ) refers. Furthermore, for example, in the bacterium Escherichia coli, another protein Tate found, which, however, evident in his function corresponds to the TatA protein. Further bacteria are known which only two of the above proteins need ( TatC and TatA in Bacillus subtilis).
Proteins that are transported via the Tat pathway, have the N-terminus a signal peptide. The name of twin - arginine translocation derived from this signal peptide, as it contains the characteristic sequence motif (S / T) - RRxFLK ( in single letter code ), which consists among other things of two adjacent arginine residues (English twin -arginine motif). After completion of transport of the protein across the membrane, the signal peptide is cleaved by a signal peptidase.