α1,4-N-Acetylhexosaminyltransferase (EXTL2) transfers GalNAc/GlcNAc from UDP- GalNAc/GlcNAc to the tetrasaccharide representing the common glycosaminoglycan (GAG)-protein linkage region (GlcAβ1-3Galβ1-3Galβ1-4Xyl), which is most likely the critical enzyme that determines and initiates heparin/heparan sulfate (HS) synthesis, distinguishing it from the chondroitin sulfate (CS)/dermatan sulfate (DS) synthesis (Kitagawa et al. 1999b). The enzyme is composed of 330 amino acids with one N- glycan and has a type II transmembrane protein topology characteristic of many other glycosyltransferases (Wuyts et al. 1997; Kitagawa et al. 1999b). The enzyme is encoded by the multiple exostoses-like gene EXTL2, a member of the hereditary multiple exos- toses (EXT) gene family of tumor suppressors (Kitagawa et al. 1999b). The enzyme protein is approximately half the size of the other EXT family members that have 676-919 amino acids. The protein shows significant homology with the carboxy- terminus of the other members of the family (Wuyts et al. 1997).
KeywordsChondroitin Sulfate Linkage Region Dermatan Sulfate Acceptor Substrate Mouse Mastocytoma
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