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Allosteric regulation of tryptophan synthase channeling: the internal aldimine probed by trans-3-indole-3'-acrylate binding

AutorCasino, Patricia ; Niks, Dimitri; Ngo, Huu; Pan, Peng; Brzovic, Peter; Blumenstein, Lars; Barends, Thomas Reinier; Schlichting, Ilme; Dunn, Michael F.
Fecha de publicación9-jun-2007
EditorAmerican Chemical Society
CitaciónBiochemistry 46(26): 7728-7739 (2007)
ResumenSubstrate channeling in the tryptophan synthase bienzyme complex from Salmonella typhimurium is regulated by allosteric interactions triggered by binding of ligand to the α-site and covalent reaction at the β-site. These interactions switch the enzyme between low-activity forms with open conformations and high-activity forms with closed conformations. Previously, allosteric interactions have been demonstrated between the α-site and the external aldimine, α-aminoacrylate, and quinonoid forms of the β-site. Here we employ the chromophoric l-Trp analogue, trans-3-indole-3‘-acrylate (IA), and noncleavable α-site ligands (ASLs) to probe the allosteric properties of the internal aldimine, E(Ain). The ASLs studied are α-d,l-glycerol phosphate (GP) and d-glyceraldehyde 3-phosphate (G3P), and examples of two new classes of high-affinity α-site ligands, N-(4‘-trifluoromethoxybenzoyl)-2-aminoethyl phosphate (F6) and N-(4‘-trifluoromethoxybenzenesulfonyl)-2-aminoethyl phosphate (F9), that were previously shown to bind to the α-site by optical spectroscopy and X-ray crystal structures [Ngo, H., Harris, R., Kimmich, N., Casino, P., Niks, D., Blumenstein, L., Barends, T. R., Kulik, V., Weyand, M., Schlichting, I., and Dunn, M. F. (2007) Synthesis and characterization of allosteric probes of substrate channeling in the tryptophan synthase bienzyme complex, Biochemistry 46, 7713−7727]. The binding of IA to the β-site is stimulated by the binding of GP, G3P, F6, or F9 to the α-site. The binding of ASLs was found to increase the affinity of the β-site of E(Ain) for IA by 4−5-fold, demonstrating for the first time that the β-subunit of the E(Ain) species undergoes a switching between low- and high-affinity states in response to the binding of ASLs.
Descripción12 pages, 4 tables, 3 schemes.-- PMID: 17559231 [PubMed].-- Printed version published Jul 3, 2007.
Versión del editorhttp://dx.doi.org/10.1021/bi700386b
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