TatB and TatC form a functional and structural unit of the twin-arginine translocase from Escherichia coli

In Escherichia coil, a subset of periplasmic proteins is exported via the t win-arginine translocation (Tat) pathway. In the present study, we have pur ified the Tat complex from E. coli, and we show that it contains only TatA, TatB, and TatC, Within the purified complex, TatB and TatC are present in a strict 1:1 ratio, suggesting a functional association. This has been conf irmed by expression of a translational fusion between TatB and TatC, This T at(BC) chimera supports efficient Tat-dependent export, indicating that Tat B and TatC act as a unit in both structural and functional terms. The purif ied Tat complex contains varying levels of TatA, suggesting a gradual loss during isolation and a looser association. The molecular mass of the comple x is similar to 600 kDa, demonstrating the presence of multiple copies of T atA, B, and C, Co-immunoprecipitation experiments show that TatC is require d for the interaction of TatA with TatB, suggesting that TatA may interact with the complex via binding to TatC.