Cell Surface Carbohydrates as Adhesion Receptors for Many Pathogenic and Opportunistic Microorganisms

Abstract

The human cell surface is covered with a layer of membrane-bound carbohydrate in the form of oligosaccharides linked covalently to lipids and proteins. The carbohydrate moieties of these glycolipids and glycoproteins form a network of outer surface projections that can serve as adhesion sites, i.e. receptors, for a variety of infectious agents which come into contact with the host cell. In many cases, the adhesion site involves a particular carbohydrate sequence which encodes a very precise binding domain that directly contributes to specificity and tissue tropism. Although carbohydrates have been recognized as possible receptors for infectious agents for quite some time (Beachey, 1981; Jones and Isaacson, 1985), it has only been within the past few years that several of these sequences have been identified and reported as possible adhesion receptors, and most of this work has been restricted to glycolipids (reviewed by Karlsson, 1989). Perhaps the major reason for this advancement is that glycolipids contain one carbohydrate moiety per molecule, allowing for less complicated analysis and identification of the carbohydrate consensus sequences involved in specific binding. Glycoproteins, on the other hand, contain several N-and/or O-linked oligosaccharides and can be clustered within heavily glycosylated regions of the peptide chain.