A family of human β4-galactosyltransferases -: Cloning and expression of two novel UDP-galactose:: β-N-acetylglucosamine β1,4-galactosyltransferases, β4Gal-T2 and β4Gal-T3

BLAST analysis of expressed sequence tags (ESTs) using the coding sequence of the human UDP-galactose:beta-N-acetylglucosamine beta 1,4-galactosyltransferase, designated beta 4Gal-T1, revealed a large number of ESTs with identical as well as similar sequences. ESTs with sequences similar to that of beta 4Gal-T1 could be grouped into at least two non-identical sequence sets. Analysis of the predicted amino acid sequence of the novel ESTs with beta 4Gal-T1 revealed conservation of short sequence motifs as well as cysteine residues previously shown to be important for the function of beta 4Gal-T1. The likelihood that the identified ESTs represented novel galactosyltransferase genes was tested by cloning and sequencing of the full coding region of two distinct genes, followed by expression. Expression of soluble secreted constructs in the baculovirus system showed that these genes represented genuine UDP-galactose:beta-N-acetylglucosamine beta 1,4-galactosyltransferases, thus designated beta 4Gal-T2 and beta 4Gal-T3. Genomic cloning of the genes revealed that they have identical genomic organizations compared with beta 4Gal-T1. The two novel genes were located on 1p32-33 and 1q23. The results demonstrate the existence of a family of homologous galactosyltransferases with related functions. The existence of multiple beta 4-galactosyltransferases with the same or overlapping functions may be relevant for interpretation of biological functions previously assigned to beta 4Gal-T1.