Our ongoing studies on the structure-function relationship of proteins specifically of glycosyltransferases and their modifiers like alpha-lactalbumin, continued this year. We report for the first time that the cDNA sequence of bovine beta (1-4) galactosyltransferase (GT) (constructed from a partial cDNA clone and a genomic fragment) engineered in an Okayama-Berg vector, upon transfection of COS-7 cells, codes for an enzymatically active CT. There is an approximately 12 fold increase in the GT activity upon transfection of COS-7 cells with sense cDNA compared to antisense or pSV(2)Neo or mock transfected cells. Polyclonal and monoclonal antibodies directed against synthetic peptide corresponding to the amino-terminal region of the GT protein, bind the expressed protein and the immunoprecipitates exhibit GT enzymatic activity. The expressed GT activity is modulated by alpha-lactalbumin to change the acceptor specificity to glucose, to synthesize lactose. These results show that the expressed GT protein is fully functional and that the binding sites for UDP-galactose, N-acetylglucosamine, glucose and alpha-lactalbumin are all intact and operative. We have also engineered the cDNA sequences of galactosyltransferase and alpha-lactalbumin, in such a way that the expression of the cDNA sequences have a potential to produce either soluble and secreted forms or membrane anchored forms of the protein.
