Rules for priming and inhibition of glycosaminoglycan biosynthesis; probing the β4GalT7 active site
Rules for priming and inhibition of glycosaminoglycan biosynthesis; probing the β4GalT7 active site
复制标题
DOI：
10.1039/c4sc01244e
复制
发表时间：
2014-09-01
期刊：
影响因子：
8.4
通讯作者：
Ellervik, Ulf
中科院分区：
文献类型：
--
作者：
Siegbahn, Anna;Manner, Sophie;Ellervik, Ulf
β-1，4-半乳糖基转移酶7（β 4GalT 7）是蛋白聚糖（PG）的糖胺聚糖（GAG）链生物合成中的必需酶。哺乳动物细胞产生PG，其参与生物过程，如细胞生长和分化。PG由一个核心蛋白组成，连接一条或几条GAG链。PG和GAG链的结构以及参与其生物合成和降解的酶的表达在正常细胞和肿瘤细胞之间不同。GAG链的生物合成通过核心蛋白的丝氨酸残基的木糖基化，随后通过β 4GalT 7的半乳糖基化来起始。生物合成也可以通过外源添加具有疏水糖苷配基的β-D-吡喃木糖苷来引发，其因此可以充当β 4GalT 7的受体底物。为了确定β 4GalT 7活性的结构要求，我们克隆并表达了该酶，并设计了具有木糖部分修饰的2-萘基β-D-吡喃木糖苷的集中文库。基于酶的研究，即半乳糖基化及其抑制，构象分析和使用晶体结构的分子建模，我们提出β 4GalT 7的结合口袋非常窄，具有一组精确的重要氢键。木糖似乎是β 4GalT 7半乳糖基化的最佳受体底物。然而，我们发现β-D-吡喃木糖苷的木糖部分的修饰可以产生半乳糖基化的抑制剂。这些化合物将是探索GAG和PG生物合成的有价值的工具，也是开发抗肿瘤药物的起点。
beta-1,4-Gatactosyltransferase 7 (beta 4GalT7) is an essential enzyme in the biosynthesis of glycosaminoglycan (GAG) chains of proteoglycans (PGs). Mammalian cells produce PGs, which are involved in biological processes such as cell growth and differentiation. The PGs consist of a core protein, with one or several GAG chains attached. Both the structure of the PGs and the GAG chains, and the expression of the enzymes involved in their biosynthesis and degradation, vary between normal cells and tumor cells. The biosynthesis of GAG chains is initiated by xylosylation of a serine residue of the core protein, followed by galactosylation by beta 4GalT7. The biosynthesis can also be initiated by exogenously added beta-D-xylopyranosides with hydrophobic aglycons, which thus can act as acceptor substrates for beta 4GalT7. To determine the structural requirements for beta 4GalT7 activity, we have cloned and expressed the enzyme and designed a focused library of 2-naphthyl beta-D-xylopyranosides with modifications of the xylose moiety. Based on enzymatic studies, that is galactosylation and its inhibition, conformational analysis and molecular modeling using the crystal structure, we propose that the binding pocket of beta 4GalT7 is very narrow, with a precise set of important hydrogen bonds. Xylose appears to be the optimal acceptor substrate for galactosylation by beta 4GalT7. However, we show that modifications of the xylose moiety of the beta-D-xylopyranosides can render inhibitors of galactosylation. Such compounds will be valuable tools for the exploration of GAG and PG biosynthesis and a starting point for development of anti-tumor agents.