Positive charges on the translocating polypeptide chain arrest movement through the translocon

J Cell Sci. 2011 Dec 15;124(Pt 24):4184-93. doi: 10.1242/jcs.086850. Epub 2012 Jan 5.

Abstract

Polypeptide chains synthesized by membrane-bound ribosomes are translocated through, and integrated into, the endoplasmic reticulum (ER) membrane by means of the protein translocation channel, the translocon. Positive charges on the nascent chain determine the orientation of the hydrophobic segment as it is inserted into the translocon and enhance the stop-translocation of translocating hydrophobic segments. Here we show that positive charges temporarily arrested ongoing polypeptide chain movement through the ER translocon by electrostatic interaction, even in the absence of a hydrophobic segment. The C-terminus of the polypeptide chain was elongated during the arrest, and then the full-length polypeptide chain moved through the translocon. The translocation-arrested polypeptide was not anchored to the membrane and the charges were on the cytoplasmic side of the membrane. The arrest effect was prevented by negatively charged residues inserted into the positive-charge cluster, and it was also suppressed by high salt conditions. We propose that positive charges are independent translocation regulators that are more active than previously believed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cytoplasm / chemistry
  • Endoplasmic Reticulum / metabolism*
  • Intracellular Membranes / metabolism
  • Membrane Proteins / analysis
  • Peptides / chemistry
  • Peptides / metabolism
  • Protein Sorting Signals*
  • Protein Transport*
  • Rats
  • Ribosomes / metabolism
  • Sodium Chloride / chemistry

Substances

  • Membrane Proteins
  • Peptides
  • Protein Sorting Signals
  • Sodium Chloride