The interplay of Hrd3 and the molecular chaperone system ensures efficient degradation of malfolded secretory proteins

M Mehnert, F Sommermeyer, M Berger… - Molecular biology of …, 2015 - Am Soc Cell Biol
M Mehnert, F Sommermeyer, M Berger, S Kumar Lakshmipathy, R Gauss, M Aebi, E Jarosch…
Molecular biology of the cell, 2015Am Soc Cell Biol
Misfolded proteins of the secretory pathway are extracted from the endoplasmic reticulum
(ER), polyubiquitylated by a protein complex termed the Hmg-CoA reductase degradation
ligase (HRD-ligase), and degraded by cytosolic 26S proteasomes. This process is termed
ER-associated protein degradation (ERAD). We previously showed that the membrane
protein Der1, which is a subunit of the HRD-ligase, is involved in the export of aberrant
polypeptides from the ER. Unexpectedly, we also uncovered a close spatial proximity of …
Misfolded proteins of the secretory pathway are extracted from the endoplasmic reticulum (ER), polyubiquitylated by a protein complex termed the Hmg-CoA reductase degradation ligase (HRD-ligase), and degraded by cytosolic 26S proteasomes. This process is termed ER-associated protein degradation (ERAD). We previously showed that the membrane protein Der1, which is a subunit of the HRD-ligase, is involved in the export of aberrant polypeptides from the ER. Unexpectedly, we also uncovered a close spatial proximity of Der1 and the substrate receptor Hrd3 in the ER lumen. We report here on a mutant Hrd3KR that is selectively defective for ERAD of soluble proteins. Hrd3KR displays subtle structural changes that affect its positioning toward Der1. Furthermore, increased quantities of the ER-resident Hsp70-type chaperone Kar2 and the Hsp40-type cochaperone Scj1 bind to Hrd3KR. Of note, deletion of SCJ1 impairs ERAD of model substrates and causes the accumulation of client proteins at Hrd3. Our data imply a function of Scj1 in the removal of malfolded proteins from the receptor Hrd3, which facilitates their delivery to downstream-acting components like Der1.
Am Soc Cell Biol