Functional protein transport is essential for all living organisms. In E. coli , approximately one third of all proteins are exported to the membranes or periplasm. The universal Sec pathway uses either a co- or post-translational process to translocate unfolded proteins through or into the inner cell membrane of bacteria. With in vivo single-molecule tracking, we aim to further elucidate the cellular roles for two of the players in the post-translational process—the ATPase SecA and the chaperone SecB. SecB binds to polypeptides in the cytosol and delivers the unfolded pre-proteins to the translocon-associated SecA. SecA drives the translocation of the polypeptides through the SecYEG translocon. Currently, we are investigating the relationship between SecA and SecB, and, among other things, the suggested co-translational targeting mechanisms for these two molecules. To do so, we make use of a newly developed camera-based single-molecule 3D tracking method that can capture fast binding kinetics. This allows us to study dynamic changes of binding states at the inner membrane at much higher detail than with conventional 2D tracking.
Wikström et al. (Sun,) studied this question.
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