Affinity of TatC sub(d) for TatA sub(d) Elucidates Its Receptor Function in the Bacillus subtilis Twin Arginine Translocation (Tat) Translocase System

• Published in: The Journal of biological chemistry 2006-07, Vol.281 (29), p.19977-19984
• Main Authors: Schreiber, Sandra, Stengel, Rayk, Westermann, Martin, Volkmer-Engert, Rudolph, Pop, Ovidiu I, Mueller, Joerg P
• Format: Article
• Language: English
• Subjects: Bacillus subtilis; Escherichia coli
• ISSN: 0021-9258; 1083-351X

Twin arginine translocation (Tat) systems catalyze the transport of folded proteins across the bacterial cytosolic membrane or the chloroplast thylakoid membrane. In the Tat systems of Escherichia coli and many other species TatA-, TatB-, and TatC-like proteins have been identified as essential translocase components. In contrast, the Bacillus subtilis phosphodiesterase PhoD-specific system consists only of a pair of TatA sub(d)/TatC sub(d) proteins and involves a TatA sub(d) protein engaged in a cytosolic and a membrane-embedded localization. Because soluble TatA sub(d) was able to bind the twin arginine signal peptide of prePhoD prior to membrane integration it could serve to recruit its substrate to the membrane via the interaction with TatC sub(d). By analyzing the distribution of TatA sub(d) and studying the mutual affinity with TatC sub(d) we have shown here that TatC sub(d) assists the membrane localization of TatA sub(d). Besides detergent-solubilized TatC sub(d), membrane-integrated TatC sub(d) showed affinity for soluble TatA sub(d). By using a peptide library-specific binding of TatA sub(d) to cytosolic loops of membrane protein TatC sub(d) was demonstrated. Depletion of TatC sub(d) in B. subtilis resulted in a drastic reduction of TatA sub(d), indicating a stabilizing effect of TatC sub(d) for TatA sub(d). In addition, the presence of the substrate prePhoD was the prerequisite for appropriate localization in the cytosolic membrane of B. subtilis as demonstrated by freeze-fracture experiments.