Endoplasmic Reticulum-Associated Degradation of Glycoproteins in Plants

Silvia Hüttner,Richard Strasser

doi:10.3389/fpls.2012.00067

Abstract

In all eukaryotes the endoplasmic reticulum (ER) has a central role in protein folding and maturation of secretory and membrane proteins. Upon translocation into the ER polypeptides are immediately subjected to folding and modifications involving the formation of disulfide bridges, assembly of subunits to multi-protein complexes, and glycosylation. During these processes incompletely folded, terminally misfolded, and unassembled proteins can accumulate which endanger the cellular homeostasis and subsequently the survival of cells and tissues. Consequently, organisms have developed a quality control system to cope with this problem and remove the unwanted protein load from the ER by a process collectively referred to as ER-associated degradation (ERAD) pathway. Recent studies in Arabidopsis have identified plant ERAD components involved in the degradation of aberrant proteins and evidence was provided for a specific role in abiotic stress tolerance. In this short review we discuss our current knowledge about this important cellular pathway.

Highlights

In all eukaryotes the endoplasmic reticulum (ER) has a central role in protein folding and maturation of secretory and membrane proteins
Organisms have developed a quality control system to cope with this problem and remove the unwanted protein load from the ER by a process collectively referred to as ER-associated degradation (ERAD) pathway
Based on the location of the misfolded lesion in the protein that is subjected to disposal, ERADL, ERADC, and ERADM substrates have been distinguished (Vashist and Ng, 2004; Bernasconi et al, 2010)

Summary

Silvia Hüttner and Richard Strasser *

Recent studies in Arabidopsis have identified plant ERAD components involved in the degradation of aberrant proteins and evidence was provided for a specific role in abiotic stress tolerance In this short review we discuss our current knowledge about this important cellular pathway. After the transfer the two terminal glucose residues are cleaved off by α-glucosidase I and II and the resulting polypeptides with monoglucosylated glycan structures are subjected to the calnexin/calreticulin cycle (Figure 1B) In this quality control process, a soluble calreticulin or the membrane-anchored calnexin binds to the monoglucosylated oligosaccharide, promotes folding, and prevents aggregation of folding intermediates (Helenius and Aebi, 2004; Caramelo and Parodi, 2008).

Arabidopsis ERAD pathway

ERAD substrate