Abstract
The Hakata antigen is a novel, thermolabile beta2-macroglycoprotein that reacts with sera from patients suffering from systemic lupus erythematosus. In this study we present the structure and the function of the Hakata antigen. We have identified cDNA clones encoding the Hakata antigen and analyzed its function. The cDNA included a possible open reading frame of 897 nucleotides, encoding 299 amino acids. The Hakata antigen consisted of a collagen-like domain in the middle section and a fibrinogen-like domain in the COOH terminus, both of which are homologous to human ficolin-1 and opsonin P35, indicating that these three molecules form a distinct family. The molecular mass of the Hakata antigen expressed in transfected cells was 35 kDa under reduced conditions, and it formed ladder bands under nonreducing conditions compatible with the previous result that the Hakata antigen exists in serum as homopolymers. Purified Hakata antigen sustained lectin activity, showing affinity with GalNAc, GlcNAc, D-fucose as mono/oligosaccharide, and lipopolysaccharides from Salmonella typhimurium and Salmonella minnesota. These results suggest that the Hakata antigen, a new member of the ficolin/opsonin P35 family, plays a role in the serum exerting lectin activity under physiological conditions.
Highlights
Inaba and Okochi [1] reported that sera from patients with systemic lupus erythematosus (SLE)1 contained an antibody that reacted with normal sera
The Hakata antigen is a novel, thermolabile 2-macroglycoprotein that reacts with sera from patients suffering from SLE [1, 2]
The amino acid sequences determined from purified Hakata antigen were completely adjusted to the deduced amino acid sequence from cloned cDNA (Figs. 1 and 2)
Summary
Inaba and Okochi [1] reported that sera from patients with systemic lupus erythematosus (SLE) contained an antibody that reacted with normal sera. All sera from 10,050 Japanese healthy blood donors, 99.99% of 751,352 Japanese patients’ sera, and 99.98% of 41,430 Swedish patients’ sera contained the Hakata antigen [4], implying that the Hakata antigen is a normal serum protein. The antibody against the Hakata antigen was possessed by 4.3% of 349 SLE patients and 0.3% of 703 patients with other autoimmune diseases [4]. Among patients with other autoimmune diseases who possessed the antibody against the Hakata antigen, one patient was found among those with chronic glomerulonephritis and another in the group with primary biliary cirrhosis. The primary structure of the Hakata antigen is partially homologous to those of human ficolin-1 [5] and opsonin P35 [6], both of which contain collagen- and fibrinogen-like domains
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