GAG glucuronyltransferase I (GlctAT-I) transfers GlcA from UDP-GlcA to the trisaccharide-serine Galβ1-3Galβ1-4Xylβ1-O-Ser, forming the GAG-protein linkage region (GlcAβ1-3Galβ1-3Galβ1-4Xylβ1-O-Ser) common to various proteoglycans. The enzyme consists of 335 amino acids with one N-glycan and has a type II trans- membrane orientation characteristic of many of the other glycosyltransferases (Kitagawa et al. 1998; Wei et al. 1999). The molecular mass of the peptide backbone is 37 kDa, but the mass of the mature protein increases with glycosylation to around 47 kDa. An additional characteristic feature in the amino acid sequence of GlcN-I is a proline-rich domain (from Pro-30 to Pro-75) next to the transmembrane region, as is seen in several other glycosyltransferases, including glucuronyltransferase-P (GlcN-P) and glucuronyltransferase-D (GlcN-D), which synthesize the precursor structure GlcAβ1-3Galβ1-4GlcNAc-R for the HNK-1 carbohydrate epitope GlcA(3-O- sulfate)β1-3Galβ1-4GlcNAc-R (Terayama et al. 1997; Seiki et al. 1999; Shimoda et al. 1999). Database searches indicate that the amino acid sequence of GlcN-I displays 43% and 46% identity to GlcN-P and GlcN-D, respectively. The highest sequence identity is found in the COOH-terminal catalytic domain, which follows the prolinerich region (252 amino acids between Pro-68 and Glu-319 overlap with about 60% identity) (Kitagawa et al. 1998; Wei et al. 1999) and contains the four previously identified highly conserved motifs (I-IV) for putative GlcAT among animal species (Terayama et al. 1997; Shimoda et al. 1999).
KeywordsChondroitin Sulfate Acceptor Substrate Repeat Disaccharide Unit Chinese Hamster Ovary Cell Mutant Embryonic Chick Brain
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