ABSTRACT
Interactions between humoral or cell-associated lectins with the exposed glycans on the cell surface of potential pathogens are considered key components of the innate immune response of vertebrates and invertebrates [1-4]. Lectins are generally organized as oligomers of noncovalently bound subunits, each displaying a carbohydrate recognition domain (CRD) that binds to the sugar ligand, usually a nonreducing terminal monosaccharide or oligosaccharide. Although lectin-ligand interactions are relatively weak as compared with other immune recognition molecules, high avidity for the target is achieved when multiple CRDs interact with ligand simultaneously [5]. In soluble collectins [2] such as the mannose-binding lectin, the subunits possessing a single CRD associate to form a “bouquet”-like oligomer with all CRDs facing the potential target surface. However, in the “cruciform” organization of the conglutinin subunits, the single CRDs are arranged in a manner that can also cross-link multiple targets. A less frequent organizational plan is the presence of tandem CRDs encoded within a polypeptide, such as observed in the macrophage mannose receptor [6], immulectins [7], and tandem repeat-type galectins [8].
