Unsaturated fatty acids augment protein transport via the SecA:SecYEG translocon

Abstract

The translocon SecYEG forms the primary protein-conducting channel in the cytoplasmic membrane of bacteria, and the associated ATPase SecA provides the energy for the transport of secretory and cell envelope protein precursors. The translocation requires negative charge at the lipid membrane surface, but its dependence on the properties of the membrane hydrophobic core is not known. Here, we demonstrate that SecA:SecYEG-mediated protein transport is immensely stimulated by unsaturated fatty acids (UFAs). Furthermore, UFA-rich tetraoleoyl-cardiolipin, but not bis(palmitoyloleoyl)-cardiolipin, facilitate the translocation via the monomeric translocon. Biophysical analysis and molecular dynamics simulations show that UFAs determine the loosely packed membrane interface, where the N-terminal amphipathic helix of SecA docks. While UFAs do not affect the translocon folding, they promote SecA binding to the membrane, and the effect is enhanced manifold at elevated ionic strength. Tight SecA:lipid interactions convert into the augmented translocation. As bacterial cells actively change their membrane composition in response to their habitat, the modulation of SecA:SecYEG activity via the fatty acids may be crucial for protein secretion over a broad range of environmental conditions.

A new technology for isolating organellar membranes provides fingerprints of lipid bilayer stress

“…This membrane distortion should also render them sensitive to the lipid composition. In fact, increased membrane stiffness from increased lipid saturation or aberrantly high sterol levels inhibits the insertion of transmembrane proteins in model membranes (Brambillasca et al , 2005), the mammalian ER (Nilsson et al , 2001), and bacterial membranes (Kamel et al , 2022). Therefore, it comes as no surprise that the stiffness and thickness of the ER membrane is continuously monitored by the UPR for regulating the relative rate of protein and lipid biosynthesis as well as the ERAD machinery (Travers et al , 2000; Schuck et al , 2009; Halbleib et al , 2017).…”