Backbone assignments for the isolated α-subunit of Salmonella typhimurium tryptophan synthase (TS) are reported based on triple resonance solution-state NMR experiments on a uniformly 2H,13C,15N-labeled sample. From the backbone chemical shifts, secondary structure and random coil index order parameters (RCI-S2) are predicted. Titration with the 3-indole-D-glycerol 3'-phosphate analog, N-(4'-trifluoromethoxybenzenesulfonyl)-2-aminoethyl phosphate (F9), leads to chemical shift perturbations indicative of conformational changes from which an estimate of the dissociation constant is obtained. Comparisons of the backbone chemical-shifts, RCI-S2 values, and site-specific relaxation times with and without F9 reveal allosteric changes including modulation in secondary structures and loop rigidity induced upon ligand binding. A comparison is made to the X-ray crystal structure of the α-subunit in the full TS αββα bi-enzyme complex and to two new X-ray crystal structures of the isolated TS α-subunit reported in this work.

中文翻译：

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来自溶液态 NMR 的鼠伤寒沙门氏菌色氨酸合酶 α 亚基的主链分配和构象动力学。


基于均匀 2H、13C、15N 标记样品的三重共振溶液态 NMR 实验，报告了分离的鼠伤寒沙门氏菌色氨酸合酶 (TS) α 亚基的主链分配。根据主链化学位移，预测二级结构和无规卷曲指数顺序参数（RCI-S2）。用 3-吲哚-D-甘油 3'-磷酸类似物 N-(4'-三氟甲氧基苯磺酰基)-2-氨乙基磷酸酯 (F9) 滴定会导​​致化学位移扰动，表明构象变化，由此可估计解离常数获得。比较有和没有 F9 的主链化学位移、RCI-S2 值和位点特异性弛豫时间揭示了变构变化，包括二级结构的调节和配体结合时诱导的环刚性。对完整 TS αββα 双酶复合物中 α 亚基的 X 射线晶体结构和本工作中报道的分离的 TS α 亚基的两种新 X 射线晶体结构进行了比较。