UNDERSTANDING THE ROLE OF LIPID MODIFICATIONS IN ER PROTEIN QUALITY CONTROL
Melissa Roberts, Clark Peterson, James Olzmann.
University of California, Berkeley, Berkeley, CA.
Endoplasmic reticulum-associated degradation (ERAD) is a cellular process responsible for the detection and degradation of misfolded proteins of the secretory pathway. Defining the mechanisms underlying this process is vital to understanding the pathogenesis of numerous human diseases that result from impaired ER protein quality control. Recent reports indicate that inhibition of acyl-CoA synthetases with the small molecule triacsin C disrupts ERAD. However, why acyl-CoA synthetases are required for ERAD remains unknown. Palmitoylation, the covalent addition of the fatty acid palmitate to a protein, requires acyl-CoA synthetase activity and can significantly impact protein localization, structure, and physical interactions. Therefore, we hypothesized that palmitoylation of ERAD machinery regulates the identification and degradation of ERAD substrates. To test this hypothesis, we employed copper-catalyzed azide-alkyne cycloaddition to probe for palmitoylated ERAD proteins. Our results reveal palmitoylation of 4 prominent ERAD proteins: the E2-recruitment factor AUP1, the E3 ligase Hrd1, the rhomboid pseudoprotease Derlin-1, and the mannosidase ERMan1, indicating that palmitoylation may regulate ERAD at multiple steps. Consistent with a functional role for palmitoylation in ERAD, we found that treatment with the palmitoylation inhibitor 2-bromopalmitate significantly attenuated ERAD. Together, our results identify an unprecedented mechanism of ERAD regulation that will broadly impact our understanding of ERAD-associated diseases.