Comparison of the three rat GDP-L-fucose :beta-D-galactoside 2-alpha-L-fucosyltransferases FTA, FTB and FTC

The complete coding sequences of three rat alpha1,2-fucosyltransferase gene s were obtained. Sequence analysis revealed that these genes, called FTA, F TB and FTC, were homologous to human FUT1, FUT2 and Sec1, respectively. A d istance analysis between all alpha1,2-fucosyltransferase sequences availabl e showed that the two domains of the catalytic region evolved differently w ith little divergence between the FUT2 and Sec1 N-terminal domains, quite d istant from that of FUT1. At variance, FUT1 and FUT2 C-terminal domains wer e less distant while a high evolutionary rate was noted for Sec1 C-terminal domain. Whereas FTA and FTB encode typical glycosyltransferases, FTC lacks the homologous start codon and encodes a protein devoid of intracellular a nd transmembrane domains. It is located on rat chromosome 1q34. Transfectio n experiments revealed that unlike FTA and FTB, FTC does not generate enzym e activity. Analysis by flow cytometry showed that H type 2 epitopes were s ynthesized in Chinese hamster ovary cells transfected by both FTA and FTB c DNA, but only FTB transfectants possessed H type 3 determinants. In REG rat carcinoma cells, both FTA and FTB allowed synthesis of H type 2 and H type 3 at the cell surface. Western blots showed that, in both cell types, FTA was able to synthesize H type 2 epitopes on a larger set of glycoproteins t han FTB. Analysis of the kinetic parameters obtained using small oligosacch arides revealed only a slight preference of FTA for type 2 over other types of acceptor substrates, whereas FTB was barely able to fucosylate this sub strate.