Signal peptides open protein-conducting channels in E. coli.
Plasma membrane vesicles and protoplasts of Escherichia coli were fused to planar lipid bilayers and studied with electrophysiological techniques. Large transmembrane aqueous channels were opened when 0.2 nM LamB signal peptide was added to the cytoplasmic side of the membrane. These aqueous pores are similar in conductance to those previously observed in mammalian endoplasmic reticulum when puromycin is used to release and thus unplug nascent translocating chains. Signal sequences have been previously shown to be necessary and sufficient for targeting proteins to cellular membranes. These results demonstrate that signal peptides are sufficient for opening the protein-conducting channels. We suggest that they are the physiological ligands that open protein-conducting channels at the initiation of protein translocation across prokaryotic plasma membrane and mammalian endoplasmic reticulum.
Simon
S M
SM
Laboratory of Cell Biology, Rockefeller University, New York, New York 10021.
Blobel
G
G
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D004553:Electric Conductivity; D004926:Escherichia coli / Q000378:metabolism*; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007473:Ion Channels / Q000378:metabolism*; D008051:Lipid Bilayers; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D018272:Porins; D021382:Protein Sorting Signals / Q000502:physiology*; D011506:Proteins / Q000378:metabolism*; D011991:Receptors, Virus / Q000737:chemistry / Q000378:metabolism*
D001425:Bacterial Outer Membrane Proteins; D007473:Ion Channels; D008051:Lipid Bilayers; D018272:Porins; D021382:Protein Sorting Signals; D011506:Proteins; D011991:Receptors, Virus; C016532:maltoporins