Lateral gate dynamics of the bacterial translocon using single molecule fluorescence

Abstract

During translation, transmembrane segments (TMs) of nascent membrane proteins emerging from the ribosome insert into the translocon (SecYEG in bacteria) and reach the phospholipid bilayer through the open lateral gate formed of two helices of SecY. We use single-molecule fluorescence resonance energy transfer (smFRET) to observe lateral-gate fluctuations in SecYEG embedded in nanodiscs containing native membrane phospholipids. We show that the lateral gate is highly dynamic with or without the ligands and propose a model-free statistical approach to describe these conformational ensembles.