Glycobiology, 2001, Vol. 11, No. 8 645-653
© 2001 Oxford University Press
1,3 galactosyltransferase: new sequences and characterization of conserved cysteine residues
3ORSP, Department of Chemistry and Biochemistry, San Francisco State University, 1600 Holloway Ave., San Francisco, CA 94132, USA, and 4Department of Chemistry, Wayne State University, Detroit, MI, USA
Nucleotide sequences were determined for 
1,3 galactosyltransferases (1,3 GalTs) from several species (bat, mink, dog, sheep, and dolphin) and compared with those previously determined for this enzyme and members of the 1,3 galactosyl/N-acetylgalactosyltransferase (1,3 Gal(NAc)Ts) family of enzymes. Sequence comparison of the newly characterized 1,3 GalT nucleotide and predicted amino acid sequences with those previously characterized for other 1,3GalT enzymes demonstrated a remarkable level of sequence identity at the nucleotide and amino acid level. The identity of each sequence as an 1,3 GalT was confirmed by expressing the encoded protein and characterizing the resulting enzyme.
The 1,3 GalTs have a significant degree of sequence homology with A and B transferases, the 1,3 GalNAcT that catalyzes the synthesis of Forssman antigen, and the recently cloned iso-globotriaosylceramide synthase. Among the conserved residues, there are two Cys residues. To determine if these conserved residues are free or involved in the formation of a disulfide bond, bovine 1,3 GalT was characterized by chemical modification and mass spectrometry. Each peptide containing a Cys residue was chemically labeled with an alkylating reagent demonstrating that these enzymes do not contain disulfide bonds. Similar results have recently been reported for A and B transferases (Yen et al., 2000, J. Mass. Spectrom., 35, 990–1002). Thus, the highly conserved Cys residues found in these members of the 1,3 Gal(NAc)Ts family of enzymes are likely involved in other important aspects of enzyme structure/function within this enzyme family.
1 These authors contributed equally to this work.
2 To whom correspondence should be addressed
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