CLONING AND CHARACTERIZATION OF THE HAKATA ANTIGEN, A MEMBER OF THE FICOLIN OPSONIN P35 LECTIN FAMILY/

The Hakata antigen is a novel, thermolabile beta(2)-macro-glycoprotein that reacts with sera from patients suffering from systemic lupus ery thematosus. In this study we present the structure and the function of the Hakata antigen. We have identified cDNA clones encoding the Hakat a antigen and analyzed its function. The cDNA included a possible open reading frame of 897 nucleotides, encoding 299 amino acids. The Hakat a antigen consisted of a collagen-like domain in the middle section an d a fibrinogen-like domain in the COOH terminus, both of which are hom ologous to human ficolin-1 and opsonin P35, indicating that these thre e molecules form a distinct family, The molecular mass of the Hakata a ntigen expressed in transfected cells was 35 kDa under reduced conditi ons, and it formed ladder bands under nonreducing conditions compatibl e with the previous result that the Hakata antigen exists in serum as homopolymers, Purified Hakata antigen sustained lectin activity, showi ng affinity with GalNAc, GlcNAc, D-fucose as mono/oligosaccharide, and lipopolysaccharides from Salmonella typhimurium and Salmonella minnes ota. These results suggest that the Hakata antigen, a new member of th e ficolin/opsonin P35 family, plays a role in the serum exerting lecti n activity under physiological conditions.