The collectins are a group of innate immune proteins structurally characterized by their content of a carbohydrate recognition domain and a collagen-like region. Collectin liver 1 (CL-L1) and collectin 11 (CL-11, alias collectin kidney 1, CL-K1) are the more recently described members of this group. Their genomic organization and protein structure reveal many similarities. However, CL-11 is a serum protein, whereas CL-L1 appears to be restricted to the cytosol of cells such as hepatocytes. Specificity analyses of the CRDs reveal some differences in their preferences for saccharides: CL-11 binds most avidly to l-fucose and d-mannose, whereas CL-L1 shows preference for d-mannose, d-fucose, N-acetylglucosamine, and surprisingly also d-galactose. CL-11 binds to various microorganisms including Escherichia coli, Candida albicans and Influenza A virus. Polymorphisms in the CL-11 gene (COLEC11) leading to deficiencies have recently been identified as causative for 3MC syndrome. The 3MC syndrome is associated with a wide spectrum of developmental features including facial dysmorphism, cognitive impairment, hearing loss and vesicorenal anomalies. Similar polymorphic associations were reported for the mannan-binding lectin-associated serine protease 3 (MASP-3), and falls into line with the observation that CL-11 is found in circulating complexes with MASP-1/3. These findings suggest dual or overlapping functions of CL-11 in innate immunity and in fetal development.
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