The superfamily of C-type animal lectins is defined by a sequence motif of the carbohydrate recognition domains (CRDs) and comprises seven groups of molecules. The soluble proteins are group I proteoglycans, group III collectins, and group VII containing the isolated CRDs.Type I membrane proteins include group IV selectins and group VI macrophage receptor sand related molecules.
Type II membrane proteins are group II hepatic lectins and group V natural killer cell receptors. The latter group has recently attracted considerable attention of the biomedical community.