Structures and functions of mammalian collectins.

Abstract

Protein-carbohydrate interactions serve multiple functions in the immune system. Many animal lectins (sugar binding proteins) mediate both pathogen recognition and cell-pathogen interactions using structurally related calcium-dependent carbohydrate recognition domains (C-type CRDs). The collectins are a group of mammalian lectins containing collagen regions. They include mannose-binding lectin (MBL), lung surfactant protein A (SP-A), lung surfactant protein D (SP-D), bovine conglutinin (BC), and collectin-43 (CL-43). Pathogen recognition by these collectins is mediated by binding of terminal monosaccharide residues characteristic of bacterial and fungal cell surfaces. The broad selectivity of the monosaccharide binding site and the geometrical arrangement of the multiple CRDs in the intact collectins explain the ability of these proteins to bind tightly to arrays of carbohydrate structures normally found on the surfaces of the micro-organisms and thus mediate discrimination between self and non-self.