EFFECTS OF N-GLYCOSYLATION ON THE FOLDING AND STRUCTURE OF PLANT-PROTEINS

The synthesis of many of the proteins that are translocated into the e ndoplasmic reticulum is accompanied by the co-translational attachment of preformed oligosaccharide chains to certain Asn residues. These gl ycans can play a variety of roles in the mature proteins, including th e one of stabilizing the protein and protecting the polypeptide backbo ne from the action of proteases. In addition, they can have a crucial function during the process of polypeptide folding, when aggregation w ith other proteins would hamper the acquisition of the native conforma tion. Their influence on protein folding can be direct, or mediated by interactions with endoplasmic reticulum-located molecular chaperones. The elucidation of the mechanisms that govern glycoprotein folding in the plant endoplasmic reticulum should contribute to the understandin g of how much plant cells rely on glycan chains to achieve the efficie nt folding of many proteins under diverse environmental conditions. In addition, a better knowledge of the level of conservation of the in v ivo folding mechanisms will be important for the exploitation of plant cells in the production of heterologous glycoproteins.