On the Potential Function of Type II Arabinogalactan Glycosylation in Regulating the Fate of Plant Secretory Proteins

In a plant-specific mode of protein glycosylation, various sugars and glycans are attached to hydroxyproline giving rise to a variety of diverse glycoproteins. The sub-family of arabinogalactan proteins is implicated in a multitude of biological functions, however, the mechanistic role of glycosylation on AGPs by type II arabinogalactans is largely elusive. Some models suggest roles of the glycans such as in ligand-receptor interactions and as localized calcium ion store. Structurally different but possibly analogous types of protein glycosylation exist in animal and yeast models and roles for glycans were suggested in determining the fate of glycoproteins by affecting intracellular sorting or proteolytic activation and degradation. At present, only few examples exist that describe how the fate of artificial and endogenous arabinogalactan proteins is affected by glycosylation with type II arabinogalactans. In addition to other roles, these glycans might act as a molecular determinant for cellular localization and protein lifetime of many endogenous proteins.