Ion Conductivity of the Bacterial Translocation Channel SecYEG Engaged in Translocation
Sprache des Titels:
While engaged in protein transport, the bacterial translocon
SecYEG must maintain the membrane barrier to small ions. The
preservation of the proton motif force was attributed to (i) cation
exclusion, (ii) engulfment of the nascent chain by the hydrophobic
pore ring, and (iii) a half-helix partly plugging the channel.
In contrast, we show here that preservation of the proton
motif force is due to a voltage-driven conformational change.
Preprotein or signal peptide binding to the purified and reconstituted
SecYEG results in large cation and anion conductivities
only when the membrane potential is small. Physiological values
of membrane potential close the activated channel. This voltage-
dependent closure is not dependent on the presence of the
plug domain and is not affected by mutation of 3 of the 6 constriction
residues to glycines. Cellular ion homeostasis is not
challenged by the small remaining leak conductance.