The protein translocation channel mediates glycopeptide export across the endoplasmic reticulum membrane

摘要

Peptides and misfolded secretory proteins are transported effi- ciently from the endoplasmic reticulum (ER) lumen to the cytosol, where the proteins are degraded by proteasomes. Protein export depends on Sec61p, the ribosome-binding core component of the protein translocation channel in the ER membrane. We found that prebinding of ribosomes abolished export of a glycopeptide from yeast microsomes. Deletion of SSH1, which encodes a ribosome- binding Sec61p homologue in the ER, had no effect on glycopep- tide export. A collection of cold-sensitive sec61 mutants displayed a variety of phenotypes: two mutants strongly defective in mis- folded protein export from the ER, sec61-32 and sec61-41, dis- played only minor peptide export defects. Glycopeptide export was severely impaired, however, in several sec61 mutants that were only marginally defective in misfolded protein export. In addition, a mutation in SEC63 strongly reduced peptide export from the ER. ER-luminal ATP was required for both misfolded protein and glycopeptide export. We conclude that the protein translocation channel in the ER membrane mediates glycopeptide transport across the ER membrane.