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Sakhrani, V. V.; Hilario, E.; Caulkins, B.G.; Hatcher-Skeers, M. E.; Fan, L.; Dunn, M. F.; Mueller, L. J. 2020. Backbone Assignments and Conformational Dynamics in the S. typhimurium Tryptophan Synthase α-Subunit from Solution-State NMR. Journal of Biomolecular NMR 74: 341-354. Full Article

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.

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