EVOLUTION OF CA2+-DEPENDENT ANIMAL LECTINS

This chapter discusses the evolution of Ca2+-dependent animal lectins. Animal lectins have been identified in various contexts, both as a result of direct searches for proteins with selective sugar-binding activities, and less systematically in the course of investigation of biological recognition processes. In spite of the enormous diversity of animal lectins, analysis of their primary structures reveals that most fall into relatively few categories. In all cases, sugar-binding activity is associated with discrete protein modules, of 115-140 amino acids, termed carbohydrate-recognition domains (CRDs). Three major groups of animal lectins (P, S, and C-types) contain CRDs with distinct sequence motifs. Animal lectins, grouped together are based on structural considerations also share certain important functional properties. The mannose-6-phosphate receptors (P-type lectins) and thiol-dependent p-galactoside-binding lectins (Stype lectins) each have relatively restricted specificity for a particular type of sugar structure. The C-type lectins, in contrast, are characterized not by a common type of sugar ligand, but by a shared dependence on Ca2 + for sugar-binding activity. © 1993 Academic Press Inc.