The TatBC complex formation suppresses a modular TatB-multimerization in Escherichia coli.

Twin-arginine translocation (Tat) systems allow the translocation of folded proteins across biological membranes of most prokaryotes. In proteobacteria, a TatBC complex binds Tat substrates and initiates their translocation after recruitment of the component TatA. TatA and TatB belong to one protein family, but only TatB forms stable complexes with TatC. Here we show that TatB builds up TatA-like modular complexes in the absence of TatC. This TatB ladder ranges from about 100 to over 880 kDa with 105+/-10 kDa increments. TatC alone can form a 250 kDa complex which could be a scaffold that can recruit TatB to form defined TatBC complexes.