Molecular cloning and expression of a third type of rabbit GDP-L- fucose:β-D-galactoside 2-α-L-fucosyltransferase

Abstract

Recent molecular investigation revealed that two closely related structural genes encode distinct GDP-L-fucose:β-D-galactoside 2-α-L- fucosyltransferases (α1,2-fucosyltransferases). Some human cancer cells or tissues may express an aberrant α1,2-fucosyltransferase other than H- and Secretor-type α1,2-fucosyltransferase. However, definite evidence of the existence of a third type of α1,2-fucosyltransferase has not been demonstrated. Here we report the molecular cloning of a third type of rabbit α1,2-fucosyltransferase (RFT-III) from a rabbit genomic DNA library. The DNA sequence included an open reading frame coding for 347 amino acids, and the deduced amino acid sequence of RFT-III showed 59 and 80% identity with those of the previously reported two types of rabbit α1,2-fucosyltransferase, RFT- I and RFT-II, respectively. COS-7 cells transfected with the RFT-III gene exhibited α1,2-fucosyltransferase activity toward phenyl-β-Gal as a substrate. Neuro2a (a murine neuroblastoma cell line) cells transfected with the RFT-III gene expressed fucosyl G(M1) (type 3 H) but not Ulex europaeus agglutinin-1 lectin reactive antigens (type 2 H). Kinetic studies revealed that RFT-III exhibits higher affinity to types 1 (Galβ1, 3GlcNAc) and 3 (Galβ1, 3GalNAc) than to type 2 (Galβ1, 4GlcNAc) oligosaccharides, which suggests that RFT-III as well as RFT-II is a Secretor-type α1,2- fucosyltransferase. RFT-III was expressed in the adult gastrointestinal tract. The RFT-I, -II, and -III genes were assigned within 90 kilobases on pulsed field gel electrophoresis analysis. These results constitute direct evidence that, at least in one mammalian species, three active α1,2- fucosyltransferases exist.