Blasco Pilar, Ståhle Jonas, Thorsheim Karin, Furevi Axel, Siegbahn Anna, Tykesson Emil, Westergren-Thorsson Gunilla, Ellervik Ulf, Widmalm Göran
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University SE-106 91 Stockholm Sweden
Center for Analysis and Synthesis, Center for Chemistry and Chemical Engineering, Lund University P.O. Box 124 SE-221 00 Lund Sweden.
RSC Adv. 2025 Jun 4;15(23):18010-18020. doi: 10.1039/d5ra00498e. eCollection 2025 May 29.
Proteoglycans (PGs) consist of a core protein with covalently bound glycosaminoglycan (GAG) chains that are linked a tetrasaccharide. PGs are important macromolecules that are involved in biological processes such as cell growth and differentiation. A key enzyme in the biosynthesis of PG GAG chains is β-1,4-galactosyltransferase 7 (β4GalT7) that catalyzes the transfer of galactose to a xylose residue in the formation of the linker tetrasaccharide. It is well known that the addition of xylosides containing naphthyl aglycones can initiate the biosynthesis of GAG chains by acting as substrates for β4GalT7. Previous studies have shown that its galactosylation ability is increased by using bioisosters, in which the anomeric oxygen is replaced with sulfur or sulfur-containing functional groups. Thus, 2-naphthyl xylosyl sulfoxides were synthesized and characterized by H and C NMR spectroscopy relying on both one- and two-dimensional experiments to differentiate the stereochemistry at the sulfur atom. Notably, the conformationally dependent coupling constants between the anomeric proton and the C2' atom of the naphthyl group were large and significant, ≥3.3 Hz, for the ()-configured compound as well as for the -glycoside and the thio-derivative whereas the corresponding coupling for the ()-configured compound and the sulfone derivative had < 0.6 Hz and < 0.5 Hz, respectively. Quantum mechanical calculations of the coupling constant corroborated the experimentally observed trends at the torsion angle. The galactosylation by β4GalT7 of the different acceptor substrates showed the highest affinity for the ()-configured compound and the sulfone derivative whereas an intermediate affinity was present for the ()-configured compound and the thio-derivative. The enzyme efficiency exhibited with the latter substrate was more than three times higher than with any other of the thio-derivatives. From molecular docking of the acceptor substrates to the UDP-galactose:β4GalT7 complex specific intermolecular interactions were identified. The binding affinity correlates with stacking to a tyrosine residue and a weak C-H⋯O hydrogen bond between the indole group of tryptophan in the enzyme and a proximate oxygen atom of sulfone and sulfinyl derivatives of 2-naphthyl xylosides.
蛋白聚糖（PGs）由核心蛋白和共价连接的糖胺聚糖（GAG）链组成，这些链通过四糖连接。PGs是参与细胞生长和分化等生物过程的重要大分子。PG GAG链生物合成中的一种关键酶是β-1,4-半乳糖基转移酶7（β4GalT7），它催化半乳糖转移到连接四糖形成过程中的木糖残基上。众所周知，添加含有萘苷元的木糖苷可以作为β4GalT7的底物启动GAG链的生物合成。先前的研究表明，通过使用生物电子等排体，其半乳糖基化能力会增强，其中异头氧被硫或含硫官能团取代。因此，合成了2-萘基木糖基亚砜，并通过1H和13C NMR光谱进行表征，依靠一维和二维实验来区分硫原子处的立体化学。值得注意的是，对于（+）构型的化合物以及α-糖苷和硫代衍生物，异头质子与萘基的C2'原子之间的构象依赖性耦合常数很大且显著，≥3.3 Hz，而对于（-）构型的化合物和砜衍生物，相应的耦合常数分别< 0.6 Hz和< 0.5 Hz。耦合常数的量子力学计算证实了在扭转角处实验观察到的趋势。β4GalT7对不同受体底物的半乳糖基化显示出对（+）构型的化合物和砜衍生物具有最高亲和力，而对（-）构型的化合物和硫代衍生物具有中等亲和力。后一种底物表现出的酶效率比任何其他硫代衍生物高出三倍以上。通过受体底物与UDP-半乳糖：β4GalT7复合物的分子对接，确定了特定的分子间相互作用。结合亲和力与堆积到酪氨酸残基以及酶中色氨酸的吲哚基团与2-萘基木糖苷的砜和亚砜衍生物的邻近氧原子之间的弱C-H⋯O氢键相关。
