Molecular cloning of a novel human collectin from liver (CL-L1)

Collectins are a C-lectin family with collagen-like sequences and carbohydr ate recognition domains. These proteins can bind to carbohydrate antigens o f microorganisms and inhibit their infection by direct neutralization and a gglutination, the activation of complement through the lectin pathway, and opsonization by collectin receptors, Here we report the cloning of a cDNA e ncoding human collectin from liver (CL-L1 (collectin liver 1)) that has typ ical collectin structural characteristics, consisting of an N-terminal cyst eine-rich domain, a collagen-like domain, a neck domain, and a carbohydrate recognition domain. The cDNA has an insert of 831 base pairs coding for a protein of 277 amino acid residues. The deduced amino acid sequence shows t hat this collectin has a unique repeat of four lysine residues in its C-ter minal area. Northern blot, Western blot, and reverse tp anscription-polymer ase chain reaction analyses showed that CL-L1 is present mainly in liver as a cytosolic protein and at low levels in placenta. More sensitive analyses by reverse transcription-polymerase chain reactions showed that most tissu es (except skeletal muscle) have CL-L1 mRNA Zoo-blot analysis indicated tha t CL-L1 is limited to mammals and birds. A chromosomal localization study i ndicated that the CL-L1 gene localizes to chromosome 8q23-q24.1, different from chromosome 10 of other human collectin genes. Expression studies of fu sion proteins lacking the collagen and N-terminal domains produced in Esche richia coli affirmed that CL-L1 binds mannose weakly. CL-L1 and recombinant CL-L1 fusion proteins do not bind to mannan columns. Analysis of the phylo genetic tree of CL-LI and other collectins indicated that CL-L1 belongs to a fourth subfamily of collectins following the mannan-binding protein, surf actant protein A, and surfactant protein D subfamilies including bovine con glutinin and collectin-43 (CL-43), These findings indicate that CL-LI may b e involved in different biological functions.