Galactose: A Specifically Recognized, Terminal Carbohydrate Moiety in Biological Processes

Glycoproteins and glycolipids carrying diverse oligosaccharide structures are involved in countless molecular interactions in physiologic and pathologic situations. Defining the specific carbohydrate moieties expressed in a particular set of molecules is a challenging task that could eventually explain how glycoproteins and glycolipids contribute to the physiology of normal cells and how their alterations could lead to pathologic states. A simple example is the ABO blood group system: in individuals with blood group B, the marker is defined by its terminal linked galactose, and substitution of its hydroxyl group at C2 by an N-acetyl group results in the formation of N-acetylgalactosamine, the blood group A marker. This review focuses on the importance of terminal linked galactose and its derivatives in different normal and pathological conditions. The involvement of various sugars residues sub-terminal to galactose and its derivatives was also evaluated on the basis of the galactosylation data taken from different publicly available carbohydrate databases. We conclude that those sugars penultimate to galactose, with their different types of linkages and anomery, contribute to the structure and functions of carbohydrate moieties with a terminal galactose.