Abstract
Mouse peptide N-glycanase (mPNGase) cleaves the N-glycan chain from misfolded glycoproteins and glycopeptides. Previously, several proteins were found to directly interact with mPNGase; among them, both mHR23B and mS4 were found to link mPNGase to the proteasome. In this study, we found that the cytoplasmic protein mp97 participates in the formation of a ternary complex containing mouse autocrine motility factor receptor (mAMFR), mp97, and mPNGase. This assemblage recruits the cytosolic mPNGase close to the endoplasmic reticulum (ER) membrane, where the retrotranslocation of misfolded glycoproteins is thought to occur. In addition to the ER membrane-associated E3 ligase mAMFR, a cytosolic protein mY33K, containing both UBA and UBX domains, was found to also directly interact with mp97. Thus, a complex containing five proteins, mAMFR, mY33K, mp97, mPNGase, and mHR23B, is formed in close proximity to the ER membrane and serves to couple the activities of retrotranslocation, ubiquitination, and deglycosylation and, thereby, route misfolded glycoproteins to the proteasome.