Glycosyltransferase polypeptide glycosyltransferases

Many different glycosyltransferase activities involved in higher plant wall biosynthesis have been identified in cell free membrane fractions, but in only a few cases has glycosyltransferase activity been retained in detergent-solubilized preparations, and in even fewer cases have any purified polypeptides been identified as plant cell wall glycosyltransferases (29,33). 

Figure 4 Ribbon diagrams of glycosyltransferases that demonstrate the different structural folds. When possible, nucleotide-donor sugars are depicted as stick models, manganese is depicted by a magenta ball, and N- and C-terminals are labeled. GT-A fold members are represented by bovine pi,4-galactosyltransferase I complexed with UDP-Gal (5) (Fig. (4)a, PDB accession number 1O0R) and by human polypeptide...

In the case of 0-fucose, there are two types of 0-fucosyltransferase (EC 2.4.1.221), specific for either EGF or TSR domains, whose action is followed by, respectively, the 1,3-iV-acetylglu-cosaminyltransferase known as Fringe or a /31,3-glucosyltransferase [143]. In mammals, there are two polypeptide-modifying xylosyltransferases (EC 2.4.2.26) which are the first of a series of glycosyltransferases required for the synthesis of the chondroitin and heparan sulfates [144]. The first residue of 0-mannosyl glycans is transferred by a heterodimeric peptide-O-mannosyltransferase in mammals [145], whereas in yeast there are a number of... 

Glycosyltransferases also appear to have extended acceptor-binding sites that allow a variety of different substrates to bind, provided that they have specific structural features. Many of the glycosyltransferases also have posttranslational modifications such as N-glycosylation, which may be required for their stability, secretion, and activity. The first enzyme in the pathway, polypeptide GalNAc-transferase, is unique in that it has a separate lectin-like domain, which may have a role in determining the affinity to already glycosylated acceptor substrates. 

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