Solution-state nuclear magnetic resonance studies of the Salmonella typhimurium tryptophan synthase complex

Tryptophan synthase (TS) is an allosteric bi-enzyme complex that catalyzes the final steps of l-tryptophan biosynthesis through tightly coupled α- and β-subunit reactions. Understanding how conformational dynamics mediate its catalytic efficiency and inter-subunit communication remains a key interest. Here, we establish that Salmonella typhimurium tryptophan synthase (StTS) is amenable to solution-state nuclear magnetic resonance (NMR) studies despite its large size (∼143 kDa). Towards this end, we optimized expression and labeling protocols to prepare ¹³CH₃-δ1-Ile-labeled StTS and obtained high-quality NMR spectra, which enabled subunit-specific resonance assignments. Addition of both α- and β-subunit ligands propagate structural and dynamic changes across the entire complex, underscoring the high degree of inter-subunit communication. Our findings validate StTS as a tractable model system for solution-state NMR, which can provide new molecular-level insights into the mechanisms of substrate channeling, conformational dynamics and allosteric regulation in TS.