Abstract
Collectins are characterized by a collagen-like sequence and a carbohydrate recognition domain and are members of the vertebrate C-type lectin superfamily. Recently, “novel collectins”, different from “classical collectins” consisting of mannan-binding lectin (MBL) and surfactant proteins A and D (SP-A and SP-D), have been found by reverse genetics. These “novel collectins” consist of collectin liver 1 (CL-L1), collectin kidney 1 (CL-K1), and collectin placenta 1 (CL-P1) and are encoded by three separate genes. Experimental findings on human and animal collectins have shown that both novel collectins and classical collectins play an important role in innate immunity. Based on our recent results and those of others, in this paper, we summarize the new biological functions of these novel collectins in embryonic morphogenesis and development.
Highlights
Collectin is a C-type lectin conserved in animals from amphioxus to mammals
Experimental findings on human and animal collectins have shown that both novel collectins and classical collectins play an important role in innate immunity
scavenger receptor AI (SR-AI) knockout mice were shown to have an increased mortality from HSV and Listeria infections [31, 32]. These results indicate that scavenger receptors including collectin placenta 1 (CL-P1) may play a role in innate immunity, CL-P1 is not a soluble-type collectin
Summary
Collectin is a C-type lectin conserved in animals from amphioxus to mammals. This protein possesses two characteristic structures, a collagen-like domain and a carbohydrate recognition domain (CRD). The introduction of the additional amino acid sequence into the mutated SP-A might be needed for the physiological capacity for complement activation and deactivation These results revealed that CL-K1 like MBL, ficolin, and C1q possesses an MASP-binding site containing a protease-binding motif. CL-P1 might control the expansion of bacteria and yeasts and regulate the amount of modified LDLs. Collagen-like domains, which have the highest homology between amino acid sequences of human and murine CL-P1 and harbor positively charged islands, may play an important role in its binding to the negatively charged substances. Results of affinity chromatography on immobilized CL-P1 and mass spectrometry-based proteomics demonstrated that CL-P1 in vascular endothelial cells can bind and endocytose neutrophil granule glycoproteins [36] These glycoproteins possess a multiclustered terminal Lex group on a heterogenous mixture of branched glycans containing partially poly-N-acetyllactosamine residues. The intraplasmic region containing the endocytosis motif, and collagen-like region has positively charged sites, suggesting that both regions might be important in signal transduction for development and for the scavenging functions of innate immunity
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