Large conformational changes of a highly dynamic pre-protein binding domain in SecA

SecA is an essential molecular motor for the translocation of proteins across the membrane via the bacterial Sec secretion system. While the Sec system is found in all cells from archaea to multicellular eukaryotes, the SecA protein is mainly found in bacteria. The mechanism of how the motor protein works on a molecular level is still under dispute but it is well established that SecA binds ATP and uses its hydrolysis for the translocation of substrates. In this work, we addressed the question of which conformational changes the protein might undergo during protein translocation. To this end, we investigated the molecular movements of SecA in the absence or the presence of ATP using single-molecule FRET measurements and in silico normal mode analyses. Our results demonstrate that the pre-protein binding domain of SecA is highly dynamic in the absence of the nucleotide and moves towards the helical wing domain in an ATP-bound state.