Gating of the bacterial protein translocation channel SecY

Description

To prevent the proton motif force from collapsing, the bacterial membrane must be impermeable to protons. Signal peptide binding is believed to open the SecY complex to allow for protein translocation across the bacterial plasma membrane. However, the binding site of the signal peptide only becomes accessible upon SecA binding in post-translational translocation or upon the action of an unknown trigger in co-translational translocation. To clarify the conundrum, we reconstituted the purified SecY complex into bilayer lipid membranes. We observed that the binding of SecA or of ribosomes to SecYEG is essential and sufficient to trigger the opening of the translocon even in the absence of a signal peptide. The pore has the ion conductivity of the plug deletion mutant [1]. Counting the number of reconstituted channels in the bilayer by both electrophysiological and fluorescent means indicates a very high open probability. The reversal potential remains at zero in asymmetrical salt concentration, thus ruling out ion selectivity. This finding suggests that in order to maintain cell viability, SecYEG is likely to adopt more than one conformation while bound to ribosomes or SecA.

Period	05 Sept 2012
Event title	Regional Biophysics Conference 2012
Event type	Conference
Location	SerbiaShow on map