prlA suppressors in Escherichia coli relieve the proton electrochemical gradient dependency of translocation of wild-type precursors.
The SecY protein of Escherichia coli is an integral membrane component of the protein export apparatus. Suppressor mutations in the secY gene (prlA alleles) have been isolated that restore the secretion of precursor proteins with defective signal sequences. These mutations have never been shown to affect the translocation of wild-type precursor proteins. Here, we report that prlA suppressor mutations relieve the proton-motive force (pmf) dependency of the translocation of wild-type precursors, both in vivo and in vitro. Furthermore, the proton-motive force dependency of the translocation of a precursor with a stably folded domain in the mature region was suppressed by prlA mutations in vitro. These data show that prlA mutations cause a general relaxation of the export apparatus rather than a specific change that results in bypassing of the recognition of the signal sequence. In addition, these results are indicative for a mechanism in which the proton-motive force stimulates translocation by altering the conformation of the translocon.
Nouwen
N
N
Department of Molecular Cell Biology, Institute of Biomembranes, Utrecht University, The Netherlands.
de Kruijff
B
B
Tommassen
J
J
D000255:Adenosine Triphosphate / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004563:Electrochemistry; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D016153:Genes, Suppressor; D011498:Protein Precursors / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000378:metabolism; D000069816:SEC Translocation Channels
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D011498:Protein Precursors; D021382:Protein Sorting Signals; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli; C057184:outer membrane protein A precursor (E coli); D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000255:Adenosine Triphosphate