Tryptophan Synthase: Structure, Function, and Subunit Interaction

The β‐Replacement‐Specific Pyridoxal‐p‐Dependent Lyases

“…Thus, NH4+ (2-6 mM), K + (8-20 mM), T1+ (0.35 a), or Rb+ are essential for activity of all bacterial tryptophanases, and their effects are antagonized by Na+ or Li' (15,105). Strong activation by NH4+ or K', and deactivation by Na+, was also observed with tyrosine phenol-lyase (108a), tryptophan synthase (106,112), and threonine and serine dehydratases from mammalian tissues, plants, and microbes (14). Absorption spectra, pH-activity dependence, and so forth (14,15,105,108a,109) indicate that potassium and ammonium ions lower the p K , of the imino N in the internal PLP-lysine aldimines increase the strength of inter-subunit cohesion and the affinities of the apoenzymes for PLP and of holoenzymes for substrate; opposite changes are induced by Na+ or Li'.…”

Indoleamine 2,3-Dioxygenase 1 Is a Lung-Specific Innate Immune Defense Mechanism That Inhibits Growth ofFrancisella tularensisTryptophan Auxotrophs

“…These two chains on May 10, 2018 by guest http://iai.asm.org/ make up the tetrameric ␣ 2 ␤ 2 tryptophan synthase enzyme complex that catalyzes the final steps in tryptophan biosynthesis. The ␣ subunits convert indole-3-glycerolphosphate to indole and glyceraldehyde 3-phosphate, while the ␤ subunits catalyze the condensation of indole and serine to tryptophan (8,25,30). The trpA and trpB genes are positioned next to each other in the Francisella genome (Fig.…”

Tryptophan synthase: a mine for enzymologists

“…Subunit association increases the substrate affinity and the rates of the a-and b-reaction [5], indicating a reciprocal modulation of structural flexibility and conformation. Association with the a-subunit also alters the reaction and substrate specificity of the b 2 subunit [5].…”

“…In the history of enzymology and structural biology, TS has served a key role because: (1) it was the first enzyme exhibiting two distinct catalytic activities, and therefore endowed with two active sites, whose spatial and functional relationship was deeply investigated; (2) it was the first enzyme for which a product formed at one site was demonstrated to be intramolecularly transferred to another site, contributing to the concept of vectorial catalysis and substrate channeling [1]; (3) it was one of the first enzymes whose naturally occurring mutants were exploited to pinpoint functional roles for individual amino acids, long before the development of site-directed mutagenesis; (4) it was the second PLP-dependent enzyme, after aspartate aminotransferase, whose structure was determined by X-ray crystallography; and (5) it has been serving as a model for allosteric intersubunit regulation, in the absence of a quaternary transition, allowing the investigation of the interplay between chemistry and dynamics energy landscapes. Given these premises, it is not surprising that a wealth of information on TS has been accumulated and frequently reviewed [2][3][4][5][6][7][8][9][10]. The overall emerging picture emphasizes the intimate link among structure, dynamics and function, making this enzyme a text-book case for understanding how catalysis is controlled and tuned by subtle protein conformational changes, triggered by chemical events taking place at more than 20 Å apart.…”