Molecular Cloning and Characterization of a Third Type of N-Glycan α2, 8-Sialyltransferase from Mouse Lung

抄録

A cDNA encoding a new α2, 8-sialyltransferase (ST8Sia IV), which exhibits activity toward the α2, 3-linked sialic acids of N-linked oligosaccharides, was cloned from a mouse lung cDNA library by means of the PCR-based approach. The predicted amino acid sequence of ST8Sia IV showed 15.2, 56.0, and 26.2% identity with those of so far cloned mouse α2, 8-sialyltransferases, i.e., GD3 synthase (ST8Sia I), STX (ST8Sia II), and Siaα2, 3Galβ1, -4G1cNAc α2, 8-sialyltransferase (ST8Sia III). ST8Sia IV exhibits high amino acid sequence identity (99.2%) with recently cloned hamster polysialyltransferase-1 gene, which is necessary to polysialic acid expression, but no enzymatic activity of the gene product was reported [Eckhardt, M. et al. (1995) Nature 373, 715-718]. The ST8Sia IV gene was strongly expressed in lung, heart, and spleen, but only weak expression of the gene was observed in brain, without remarkable developmental regulation. The activity of mouse ST8Sia IV was specific toward sialylated glycoproteins. The linkage-specific sialidase treatment of glycoproteins as well as N-linked oligosaccharides from the glycoproteins revealed that ST8Sia IV exhibits an α2, 8-sialyltransferase activity toward α2, 3-linked sialic acids of N-linked oligosaccharides. In addition, ST8Sia IV can synthesize polysialic acid chain in vitro without any initiator sialyltransferase.