Abstract
Carbohydrate Binding Protein 35 (CBP35) is a galactose-specific lectin belonging to the L-30 subgroup of the S-type family of animal lectins. The polypeptide chain (Mr-35, 000) consists of two distinct domains: a proline- and glycine-rich domain at the amino-terminal half and a carbohydrate recognition domain at the carboxyl-terminal half. The amino acid sequence information also indicates that CBP35 is identical to (within a given species) or homologous with (between species) proteins isolated and studied under other names: (i) L-34, a tumor cell lectin; (ii) human and rat lung lectins, HL-29 and RL-29; (iii) IgE-binding protein, εBP; (iv) LBP, a non-integrin type laminin-binding protein; and (v) Mac-2, a cell surface marker of thioglycollate-elicited macrophages. It is curious that the same polypeptide, under different guises, is found in two topologically distinct compartments of a cell: intracellular (cytosol and nucleus) and extracellular (cell surface and medium). Studies of the possible function (s) of this protein have, in turn, been guided by this dual localization: as a cell surface receptor for carbohydrate-containing ligands, including laminin and IgE, and as a nucleocytoplasmic shuttle in the form of a ribonucleoprotein complex.
