Publications

• Three-dimensional structure of the tryptophan synthase alpha 2 beta 2 multienzyme complex from Salmonella typhimurium.

  Hyde C.C., Ahmed S.A., Padlan E.A., Miles E.W., Davies D.R.

  The three-dimensional structure of the alpha 2 beta 2 complex of tryptophan synthase from Salmonella typhimurium has been determined by x-ray crystallography at 2.5 A resolution. The four polypeptide chains are arranged nearly linearly in an alpha beta beta alpha order forming a complex 150 A long ... >> More

  The three-dimensional structure of the alpha 2 beta 2 complex of tryptophan synthase from Salmonella typhimurium has been determined by x-ray crystallography at 2.5 A resolution. The four polypeptide chains are arranged nearly linearly in an alpha beta beta alpha order forming a complex 150 A long. The overall polypeptide fold of the smaller alpha subunit, which cleaves indole glycerol phosphate, is that of an 8-fold alpha/beta barrel. The alpha subunit active site has been located by difference Fourier analysis of the binding of indole propanol phosphate, a competitive inhibitor of the alpha subunit and a close structural analog of the natural substrate. The larger pyridoxal phosphate-dependent beta subunit contains two domains of nearly equal size, folded into similar helix/sheet/helix structures. The binding site for the coenzyme pyridoxal phosphate lies deep within the interface between the two beta subunit domains. The active sites of neighboring alpha and beta subunits are separated by a distance of about 25 A. A tunnel with a diameter matching that of the intermediate substrate indole connects these active sites. The tunnel is believed to facilitate the diffusion of indole from its point of production in the alpha subunit active site to the site of tryptophan synthesis in the beta active site and thereby prevent its escape to the solvent during catalysis. << Less

  J. Biol. Chem. 263:17857-17871(1988) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• ON THE SEPARATION OF THE TRYPTOPHAN SYNTHETASE OF ESCHERICHIA COLI INTO TWO PROTEIN COMPONENTS.

  Crawford I.P., Yanofsky C.

  Proc Natl Acad Sci U S A 44:1161-1170(1958) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Tryptophan biosynthetic genes in eukaryotic microorganisms.

  Hutter R., Niederberger P., DeMoss J.A.

  In recent years more information about tryptophan biosynthesis in eukaryotic microorganisms has become available. The emphasis has been on genetics and biochemistry of the pathway. Eukaryotes manifest a trend toward fewer genes and toward multifunctional proteins, while prokaryotes have a greater ... >> More

  In recent years more information about tryptophan biosynthesis in eukaryotic microorganisms has become available. The emphasis has been on genetics and biochemistry of the pathway. Eukaryotes manifest a trend toward fewer genes and toward multifunctional proteins, while prokaryotes have a greater tendency toward separate activity domains but the genes tend to be clustered genetically. Cloning of various structural tryptophan biosynthetic genes and studies on their expression in homologous and heterologous hosts have made it possible to analyze promoter structures in detail and to define structural elements involved in regulated gene expression. Comparisons of homologous genes from different organisms have highlighted the conservation of the activity domains or parts therefrom involved in the catalysis of single steps. These studies also point to a stringent maintenance of domains responsible for protein-protein aggregation. Physiological studies will be facilitated by the availability of single cloned genes and especially the artificial gene cluster containing all five TRP genes from yeast. The range of physiological manipulation has thus been enormously broadened. With chromosomal mutations it has been possible to study primarily downward modulation of a pathway. We can now initiate studies on upward modulation, since enzyme levels appear to increase in proportion to gene dose. The new range of downward and upward modulation in the levels of single enzymes and combinations of enzymes may contribute to a better understanding of flux regulation and its influence on the overall physiology of an organism. << Less

  Annu Rev Microbiol 40:55-77(1986) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Mechanisms of monovalent cation action in enzyme catalysis: the tryptophan synthase alpha-, beta-, and alpha beta-reactions.

  Woehl E., Dunn M.F.

  The alpha-subunit of the tryptophan synthase bienzyme complex catalyzes the formation of indole from the cleavage of 3-indolyl-D-glyceraldehyde 3'-phosphate, while the beta-subunit utilizes L-serine and the indole produced at the alpha-site to form tryptophan. The replacement reaction catalyzed by ... >> More

  The alpha-subunit of the tryptophan synthase bienzyme complex catalyzes the formation of indole from the cleavage of 3-indolyl-D-glyceraldehyde 3'-phosphate, while the beta-subunit utilizes L-serine and the indole produced at the alpha-site to form tryptophan. The replacement reaction catalyzed by the beta-subunit requires pyridoxal 5'-phosphate (PLP) as a cofactor. The beta-reaction occurs in two stages: in stage I, the first substrate, L-Ser, reacts with the enzyme-bound PLP cofactor to form an equilibrating mixture of the L-Ser Schiff base, E(Aex1), and the alpha-aminoacrylate Schiff base intermediate, E(A-A); in stage II, this intermediate reacts with the second substrate, indole, to form tryptophan. Monovalent cations (MVCs) are effectors of these processes [Woehl, E., and Dunn, M. F. (1995) Biochemistry 34, 9466-9476]. Herein, detailed kinetic dissections of stage II are described in the absence and in the presence of MVCs. The analyses presented complement the results of the preceding paper [Woehl, E., and Dunn, M. F. (1999) Biochemistry 38, XXXX-XXXX], which examines stage I, and confirm that the chemical and conformational processes in stage I establish the presence of two slowly interconverting conformations of E(A-A) that exhibit different reactivities in stage II. The pattern of kinetic isotope effects on the overall activity of the beta-reaction shows an MVC-mediated change in rate-limiting steps. In the absence of MVCs, the reaction of E(A-A) with indole becomes the rate-limiting step. In the presence of Na+ or K+, the conversion of E(Aex1) to E(A-A) is rate limiting, whereas some third process not subject to an isotope effect becomes rate determining for the NH4+-activated enzyme. The combined results from the preceding paper and from this study define the MVC effects, both for the reaction catalyzed by the beta-subunit and for the allosteric communication between the alpha- and beta-sites. Partial reaction-coordinate free energy diagrams and simulation studies of MVC effects on the proposed mechanism of the beta-reaction are presented. << Less

  Biochemistry 38:7131-7141(1999) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.