HUMAN MANNOSE-BINDING PROTEIN CARBOHYDRATE-RECOGNITION DOMAIN TRIMERIZES THROUGH A TRIPLE ALPHA-HELICAL COILED-COIL

Human mannose-binding protein is a hexamer of trimers with each subuni t consisting of an amino-terminal region rich in cysteine, 19 collagen repeats, a 'neck', and a carbohydrate recognition domain that require s calcium to bind ligand. A 148-residue peptide, consisting of the 'ne ck' and carbohydrate recognition domains forms trimers in solution and in crystals. The structure of this trimeric peptide has been determin ed in two different crystal forms. The 'neck' forms a triple alpha-hel ical coiled-coil. Each alpha-helix interacts with a neighbouring carbo hydrate recognition domain. The spatial arrangement of the carbohydrat e recognition domains suggest how MBP trimers form the basic recogniti on unit for branched oligosaccharides on microorganisms.