Abstract
Bacterial periplasmic proteins use the Sec machinery or the TAT pathway for translocation across the plasma membrane. Precursors transported by the Sec machinery are unfolded before translocation, while precursors transported by the TAT pathway have pre-bound cofactors or have been oligomerized. We have characterized periplasmic substrate-binding proteins (NrtA and CmpA) of ABC transporters in Synechococcus sp. PCC7942 that have 47% identity to each other. These proteins have characteristic signal peptide for the TAT pathway. We have shown that the *TAT* signal peptide was essential for the function of the NrtA protein. In this report, we show that the CmpA protein forms tetramer. These findings suggest that the TAT pathway is required for the tetrameric structure of the substrate-binding proteins and the tetrameric structure is required for the function of these proteins. We are characterizing the relationship between the TAT pathway and the tetrameric structure of these proteins.
