Enzymatic comparison and expression pattern of pig B4GALNT2 and B4GALNT2-like proteins

Objectives: The final step in the production of the human Sd(a) antigen is catalyzed by beta-1,4-N-acetyl-galactosamine transferase 2 (B4GALNT2). This is done by adding a N-acetylgalactosamine residue via a beta-1,4 linkage to a subterminal galactose residue that has been substituted with an alpha-2,3-linked sialic acid. The final stage of the production of the Cad antigen is also catalyzed by B4GALNT2. Knocking out pig B4GALNT2 gene decreased human serum antibodies binding to pig cells, which greatly reduces the immunological rejection in clinical xenotransplantation trials. Interestingly, gene region LOC110255214 (hereafter named B4GALNT2-like) showed high similarity with the B4GALNT2 gene in the pig genome in our previous work, but whether B4GALNT2-like shares similar biological properties like B4GALNT2 remains to be elucidated, whether B4GALNT2-like is a potential immune gene in xenotransplantation remains to be determined.Methods: In this study, we compared the tissue expression pattern of B4GALNT2-like and B4GALNT2 in Bama pigs.Results: We found the expression of B4GALNT2-like was significantly higher in the duodenum, but lower in the heart, spleen, lung, kidney, comparing to B4GALNT2. Applied the Escherichia coli recombinant expression, we obtained 768 and 1,300 mu g protein for B4GALNT2 and B4GALNT2-like from 1 L culture, respectively. Using the expressed recombinant proteins, the enzymatic activity of the two proteins was determined and compared.Conclusions: The enzymatic assay showed that B4GALNT2-like has comparable catalytic activity with B4GALNT2 (58.7 % of B4GALNT2), addressing an important question whether B4GALNT2-like is a new immunological rejection gene.