Targeting and Integration of Bacterial Membrane Proteins
Patrick Kuhn, Renuka Kudva, Thomas Welte, Lukas Sturm, and Hans-Georg Koch
from: Bacterial Membranes: Structural and Molecular Biology (Edited by: Han Remaut and Rémi Fronzes). Caister Academic Press, U.K. (2014)
Membrane proteins execute a plethora of essential functions in bacterial cells and therefore bacteria utilize efficient strategies to ensure that these proteins are properly targeted and inserted into the membrane. Most bacterial inner membrane proteins are recognized early during their synthesis, i.e. co-translationally by the bacterial signal recognition particle (SRP), which delivers the ribosome-nascent chain (RNC) via its interaction with the membrane-bound SRP receptor to the SecYEG translocon, a highly dynamic and evolutionarily conserved protein conducting channel. Membrane protein insertion via SecYEG is coupled to ongoing polypeptide chain elongation at the ribosome and the emerging transmembrane helices exit the SecYEG channel laterally into the lipid phase. Lateral release and folding of transmembrane helices is most likely facilitated by YidC, which transiently associates with the SecYEG translocon. YidC has also been shown to facilitate insertion of inner membrane proteins independently of the SecYEG translocon. The targeting of outer membrane proteins to SecYEG occurs predominantly post-translationally by the SecA/SecB pathway and thus follows the same route as periplasmic proteins. In this chapter, we summarize the current knowledge on membrane protein targeting and transport/integration by either SecYEG or YidC read more ...