Towards the role of TatA and TatB in the activity and stability of thylakoidal Tat translocase

Abstract

Protein sorting and transport are fundamental processes in eukaryotic cells. In chloroplasts, twin-arginine translocation (Tat) translocase mediates the transport of folded proteins across thylakoid membranes, which consists of TatA, TatB and TatC subunits. Here, in thylakoidal reconstitution assays were used to investigate the roles of individual Tat subunits. Only one of three in vitro translation systems supported functional TatB reconstitution, leading to the use of purified TatA and TatB for further quantitative studies. Unexpectedly, high concentrations of either protein reduced intrinsic Tat transport. BN-PAGE revealed that external TatA destabilizes TatBC complexes, although TatBC signal intensities did not correlate linearly with transport activity. Moreover, TatB could substitute for TatA, whereas TatA could not replace TatB. Finally, the proton motive force was shown to influence TatBC stability, highlighting the dynamic regulation of the chloroplast Tat translocase.