Studying Glycan-Dependent ERAD of Misfolded Glycoproteins in Plants

The endoplasmic reticulum (ER) is the site where proteins that are synthesized and destined for the secretory pathway fold into their native conformations. Genetic mutations, oxidative stress, reduced glycosylation, and disruption to ER folding and quality control systems are all factors that have been demonstrated to impair this process, leading to the production of misfolded proteins. It is imperative for the survival of cells that these misfolded proteins are recognized by specific signals and directed towards degradation via ER-associated degradation (ERAD), ER-phagy, or related ER-to-lysosome/vacuole transport processes. A pivotal step in this process is the recognition of specific degrons and the distinction between terminally misfolded proteins that necessitate clearance and folding intermediates that have the potential to reach their final conformation. A significant proportion of proteins that traverse the secretory pathway in eukaryotes undergo N-glycosylation. The attached N-glycans not only facilitate the folding and quality control of glycoproteins, but can also be processed to display a glycan degron signal necessary to initiate ERAD of glycoproteins. Here, we describe methods for investigating glycan-related degrons that are key determinants for the ERAD of misfolded glycoproteins in plants.