Molecular and structural basis for N-glycan-dependent determination of glycoprotein fates in cells

Background: N-linked oligosaccharides operate as tags for protein quality control, consigning glycoproteins to different fates. i.e. folding in the endoplasmic reticulum (ER), vesicular transport between the ER and the Golgi complex, and ER-associated degradation of glycoproteins, by interacting with a panel of intracellular lectins in the early secretory pathway. Scope of review: This review summarizes the current state of knowledge regarding the molecular and structural basis for glycoprotein-fate determination in cells that is achieved through the actions of the intracellular lectins and its partner proteins. Major conclusions: Cumulative frontal affinity chromatography (FAC) data demonstrated that the intracellular lectins exhibit distinct sugar-binding specificity profiles. The glycotopes recognized by these lectins as fate determinants are embedded in the triantennary structures of the high-mannose-type oligosaccharides and are exposed upon trimming of the outer glucose and mannose residues during the N-glycan processing pathway. Furthermore, recently emerged 3D structural data offer mechanistic insights into functional interplay between an intracellular lectin and its binding partner in the early secretory pathway. General significance: Structural biology approaches in conjunction with FAC methods provide atomic pictures of the mechanisms behind the glycoprotein-fate determination in cells. This article is a part of a Special issue entitled: Glycoproteomics. (C) 2011 Elsevier B.V. All rights reserved.