From legumes to leukocytes: Biological roles for sulfated carbohydrates

Carbohydrates attached to proteins and lipids characteristically display complex and heterogeneous structures. However, it is becoming increasingly clear that carbohydrates with definite biological functions also exhibit unique structural features. A number of glycoproteins and glycolipids have been shown to bear oligosaccharides containing sulfate. Often, addition of a sulfate moiety turns a relatively common structural motif into a unique carbohydrate with the potential to be recognized by a specific receptor or lectin. This is clearly the case in three systems in which sulfated oligosaccharides have been shown to play a well-defined biological role: 1) control of the circulatory half-life of luteinizing hormone, 2) symbiotic interactions between leguminous plants and nitrogen-fixing bacteria, and 3) homing of lymphocytes to lymph nodes. The rapidly growing list of glycoproteins and glycolipids identified as bearing sulfated oligosaccharides suggests that sulfated carbohydrates play important biological roles in numerous other systems as well.