The enzyme β4-galactosyltransferase-I (β4GalT-I; UDP-Gal:GlcNAc β4-galactosyltransferase; EC 126.96.36.199) is a constitutively expressed, trans-Golgi resident, type II membrane-bound glycoprotein that is widely distributed in vertebrates. The protein domain structure established for β4GalT-I consists of: (1) a short NH2-terminal cytoplasmic domain of 11 or 24 amino acids depending on the protein isoform (Shaper et al. 1988; Russo et al. 1990); (2) a large COOH-terminal luminal domain containing the catalytic center (~270 amino acids) linked to a single transmembrane domain (19 amino acids) through a glycosylated peptide segment (~86 amino acids) termed the stem region. In essentially all vertebrate tissues, the primary function of β4GalT-I is to catalyze the transfer of Gal from UDP-Gal to GlcNAcβ-R, forming the N-acetyllactosamine (Galβ1-4GlcNAcβ1-R) or poly-N-acetyllactosamine structures assembled on glycoconjugates.
KeywordsMammary Gland Round Spermatid Stem Region Acceptor Substrate Golgi Membrane
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