Gating of the bacterial protein translocation channel SecY
Sprache des Vortragstitels:
Regional Biophysics Conference 2012
Sprache des Tagungstitel:
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 .
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.