13 - Structure and Function of Plant Glycoproteins

Abstract

This chapter discusses the structure and function of plant glycoproteins. Glycoproteins are proteins that contain glycosidic substituents; a firm covalent attachment is present between sugars and protein. Glycoproteins are not the easiest molecules to purify and characterize partly because of variable glycosylation produced during or after their biosynthesis, and partly because the carbohydrate component often imparts anomalous properties to the protein. A given glycoprotein often exhibits varying degrees of glycosylation and microheterogeneity can appear chromatographically or electrophoretically as a puzzling collection of closely physically related peaks or bands but of uncertain affinity. Compositional heterogeneity implies that the composition of similar oligosaccharide units varies. This variation can occur at the periphery of the oligosaccharide or in the central region or core. Microheterogeneity can be because of the lack of glycosyltransferase specificity or it can result from tissue-specific glycosylation or artifactually by enzymatic attack during extraction or by chemical changes during extraction and purification procedures involving alkaline conditions.