Human tumor suppressor EXT gene family members EXTL1 and EXTL3 encode α1,4-N-acetylglucosaminyltransferases that likely are involved in heparan sulfate/heparin biosynthesis
Human tumor suppressor EXT gene family members EXTL1 and EXTL3 encode α1,4-N-acetylglucosaminyltransferases that likely are involved in heparan sulfate/heparin biosynthesis
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DOI：
10.1073/pnas.131188498
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发表时间：
2001-06-19
影响因子：
11.1
通讯作者：
Sugahara, K
中科院分区：
文献类型：
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作者：
Kim, BT;Kitagawa, H;Sugahara, K
肿瘤抑制因子EXT 1和EXT 2与遗传性多发性外生骨疣相关，并编码硫酸乙酰肝素（HS）及其类似物肝素（Hep）链聚合所必需的双功能糖基转移酶。目前已克隆出三个高度同源的类EXT基因EXTL 1-EXTL 3，其中EXTL 2是一个α 1，4-GlcNAc转移酶I，是启动HS/Hep合成的关键酶。在本研究中，缺失假定的NH 2-末端跨膜和胞质结构域的EXTL 1和EXTL 3的截短形式在COS-1细胞中瞬时表达，并发现具有α-GlcNAc转移酶活性。EXTL 3不仅使用代表生长的HS链的N-乙酰肝素原寡糖，而且使用GlcA β 1 -3Gal β 1-O-C2 H4 NH-苄氧羰基（Cbz），这是决定和启动HS/Hep合成的α-GlcNAc转移酶1的合成底物。相比之下，EXTL 1仅使用前受体。用N-乙酰肝素原寡糖检测，EXTL 1和EXTL 3均未显示任何葡萄糖醛酸转移酶活性。每种转移酶反应产物的肝素酶1消化表明GlcNAc仅通过α 1，4-构型转移。因此，EXTL 3最有可能参与链的起始和延伸，而EXTL 1可能仅参与HS的链延伸，也可能参与Hep的链延伸。因此，除了具有相同特异性的EXT 1和EXT 2之外，它们的五个家族成员的受体特异性是重叠的但彼此不同。目前已证实，所有五个克隆的人EXT基因家族蛋白都具有糖基转移酶活性，这可能有助于HS和Hep的合成。
The tumor suppressors EXT1 and EXT2 are associated with hereditary multiple exostoses and encode bifunctional glycosyltransferases essential for chain polymerization of heparan sulfate (HS) and its analog, heparin (Hep). Three highly homologous EXT-like genes, EXTL1-EXTL3, have been cloned, and EXTL2 is an alpha1,4-GlcNAc transferase I, the key enzyme that initiates the HS/Hep synthesis. In the present study, truncated forms of EXTL1 and EXTL3, lacking the putative NH2-terminal transmembrane and cytoplasmic domains, were transiently expressed in COS-1 cells and found to harbor alpha -GlcNAc transferase activity. EXTL3 used not only N-acetylheparosan oligosaccharides that represent growing HS chains but also GlcA beta1-3Gal beta1-O-C2H4NH-benzyloxycarbonyl (Cbz), a synthetic substrate for alpha -GlcNAc transferase 1 that determines and initiates HS/Hep synthesis. In contrast, EXTL1 used only the former acceptor. Neither EXTL1 nor EXTL3 showed any glucuronyltransferase activity as examined with N-acetylheparosan oligosaccharides. Heparitinase 1 digestion of each transferase-reaction product showed that GlcNAc had been transferred exclusively through an alpha1,4-configuration. Hence, EXTL3 most likely is involved in both chain initiation and elongation, whereas EXTL1 possibly is involved only in the chain elongation of HS and, maybe, Hep as well. Thus, their acceptor specificities of the five family members are overlapping but distinct from each other, except for EXT1 and EXT2 with the same specificity. It now has been clarified that all of the five cloned human EXT gene family proteins harbor glycosyltransferase activities, which probably contribute to the synthesis of HS and Hep.