CL-46, a novel collectin highly expressed in bovine thymus and liver.

Collectins are oligomeric molecules with C-type lectin domains attached to collagen-like regions via alpha-helical neck regions. They bind nonself glycoconjugates on the surface of microorganisms and inhibit infection by direct neutralization, agglutination, or opsonization. During the characterization of the gene encoding bovine CL-43 (43-kDa collectin), we identified a novel collectin-gene. We report the cloning and partial characterization of the novel collectin CL-46. The mRNA comprises 1188 nucleotides encoding a protein of 371 aa with an included leader peptide of 20 residues. CL-46 has two cysteine residues in the N-terminal segment, a potential N-glycosylation site in the collagen region, and an extended hydrophilic loop close to the binding site of the carbohydrate recognition domain. It is expressed in the thymus, liver, mammary gland, and tissues of the digestive system. Recombinant CL-46 corresponding to the alpha-helical neck region and the C-type lectin domain binds preferential N-acetyl-D-glucoseamine and N-acetyl-D-mannoseamine. The gene encoding CL-46 spans approximately 10 kb and consists of eight exons, with high structural resemblance to the gene encoding human surfactant protein D. It is located on the bovine chromosome 28 at position q1.8 together with the gene encoding conglutinin and CL-43. Several potential thymus-related cis-regulatory elements were identified in the 5'-upstream sequence, indicating that the expression in thymus may be modulated by signals involved in T cell development.