Primary structure of rat liver mannan-binding protein deduced from its cDNA sequence

cDNA clones encoding rat liver mannan-binding protein (MBP), a lectin specific for mannose and N-acetylglucosamine, were isolated from a rat liver cDNA library carried in λgt 11, by screening with affinity purified polyclonal rabbit anti-rat liver MEP antibodies. The nucleotide sequence of the cDNA determined by the dideoxy method revealed the complete amino acid sequence of the MBP (226 residues). The NH₂-terminal residue of the MBP, glutamic acid, was preceded by a predominantly hydrophobic stretch of 18 amino acids, which was assumed to be a signal peptide. Near the NH₂-terminal, there was a collagen-like domain, which consisted of 19 repeats of the sequence Gly-X-Y. Here, X and Y were frequently proline and lysine. Three proline and lysine residues were hydroxylated, and one of the latter appeared to link to galactose. Computer analysis of several lectins for sequence homology suggested that the COOH-terminal quarter of the MBP is associated with the calcium binding as well as carbohydrate recognition.