Tags

Type your tag names separated by a space and hit enter

On the structural basis of the catalytic mechanism and the regulation of the alpha subunit of tryptophan synthase from Salmonella typhimurium and BX1 from maize, two evolutionarily related enzymes.
J Mol Biol. 2005 Sep 23; 352(3):608-20.JM

Abstract

Indole is a reaction intermediate in at least two biosynthetic pathways in maize seedlings. In the primary metabolism, the alpha-subunit (TSA) of the bifunctional tryptophan synthase (TRPS) catalyzes the cleavage of indole 3-glycerol phosphate (IGP) to indole and d-glyceraldehyde 3-phosphate (G3P). Subsequently, indole diffuses through the connecting tunnel to the beta-active site where it is condensed with serine to form tryptophan and water. The maize enzyme, BX1, a homolog of TSA, also cleaves IGP to G3P and indole, and the indole is further converted to 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one, a secondary plant metabolite. BX1 cleaves IGP significantly faster to G3P and indole than does TSA. In line with their different biological functions, these two evolutionary related enzymes differ significantly in their regulatory aspects while catalyzing the same chemistry. Here, the mechanism of IGP cleavage by TSA was analyzed using a novel transition state analogue generated in situ by reaction of 2-aminophenol and G3P. The crystal structure of the complex shows an sp3-hybridized atom corresponding to the C3 position of IGP. The catalytic alphaGlu49 rotates to interact with the sp3-hybridized atom and the 3' hydroxyl group suggesting that it serves both as proton donor and acceptor in the alpha-reaction. The second catalytic residue, alphaAsp60 interacts with the atom corresponding to the indolyl nitrogen, and the catalytically important loop alphaL6 is in the closed, high activity conformation. Comparison of the TSA and TSA-transition state analogue structures with the crystal structure of BX1 suggests that the faster catalytic rate of BX1 may be due to a stabilization of the active conformation: loop alphaL6 is closed and the catalytic glutamate is in the active conformation. The latter is caused by a substitution of the residues that stabilize the inactive conformation in TRPS.

Authors+Show Affiliations

Kulik V
Max Planck Institut fur medizinische Forschung, Abteilung fur Biomolekulare Mechanismen, Jahnstr. 29, 69120 Heidelberg, Germany.
Hartmann E
No affiliation info available
Weyand M
No affiliation info available
Frey M
No affiliation info available
Gierl A
No affiliation info available
Niks D
No affiliation info available
Dunn MF
No affiliation info available
Schlichting I
No affiliation info available

MeSH

Bacterial ProteinsCatalysisCatalytic DomainCrystallography, X-RayEvolution, MolecularModels, ChemicalPlant ProteinsProtein ConformationProtein Structure, QuaternaryProtein SubunitsSalmonella typhimuriumTryptophan SynthaseZea mays

Pub Type(s)

Comparative Study
Journal Article
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

16120446

Citation

Kulik, Victor, et al. "On the Structural Basis of the Catalytic Mechanism and the Regulation of the Alpha Subunit of Tryptophan Synthase From Salmonella Typhimurium and BX1 From Maize, Two Evolutionarily Related Enzymes." Journal of Molecular Biology, vol. 352, no. 3, 2005, pp. 608-20.
Kulik V, Hartmann E, Weyand M, et al. On the structural basis of the catalytic mechanism and the regulation of the alpha subunit of tryptophan synthase from Salmonella typhimurium and BX1 from maize, two evolutionarily related enzymes. J Mol Biol. 2005;352(3):608-20.
Kulik, V., Hartmann, E., Weyand, M., Frey, M., Gierl, A., Niks, D., Dunn, M. F., & Schlichting, I. (2005). On the structural basis of the catalytic mechanism and the regulation of the alpha subunit of tryptophan synthase from Salmonella typhimurium and BX1 from maize, two evolutionarily related enzymes. Journal of Molecular Biology, 352(3), 608-20.
Kulik V, et al. On the Structural Basis of the Catalytic Mechanism and the Regulation of the Alpha Subunit of Tryptophan Synthase From Salmonella Typhimurium and BX1 From Maize, Two Evolutionarily Related Enzymes. J Mol Biol. 2005 Sep 23;352(3):608-20. PubMed PMID: 16120446.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - On the structural basis of the catalytic mechanism and the regulation of the alpha subunit of tryptophan synthase from Salmonella typhimurium and BX1 from maize, two evolutionarily related enzymes. AU - Kulik,Victor, AU - Hartmann,Elisabeth, AU - Weyand,Michael, AU - Frey,Monika, AU - Gierl,Alfons, AU - Niks,Dimitri, AU - Dunn,Michael F, AU - Schlichting,Ilme, PY - 2005/05/13/received PY - 2005/07/03/revised PY - 2005/07/06/accepted PY - 2005/8/27/pubmed PY - 2005/10/20/medline PY - 2005/8/27/entrez SP - 608 EP - 20 JF - Journal of molecular biology JO - J Mol Biol VL - 352 IS - 3 N2 - Indole is a reaction intermediate in at least two biosynthetic pathways in maize seedlings. In the primary metabolism, the alpha-subunit (TSA) of the bifunctional tryptophan synthase (TRPS) catalyzes the cleavage of indole 3-glycerol phosphate (IGP) to indole and d-glyceraldehyde 3-phosphate (G3P). Subsequently, indole diffuses through the connecting tunnel to the beta-active site where it is condensed with serine to form tryptophan and water. The maize enzyme, BX1, a homolog of TSA, also cleaves IGP to G3P and indole, and the indole is further converted to 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one, a secondary plant metabolite. BX1 cleaves IGP significantly faster to G3P and indole than does TSA. In line with their different biological functions, these two evolutionary related enzymes differ significantly in their regulatory aspects while catalyzing the same chemistry. Here, the mechanism of IGP cleavage by TSA was analyzed using a novel transition state analogue generated in situ by reaction of 2-aminophenol and G3P. The crystal structure of the complex shows an sp3-hybridized atom corresponding to the C3 position of IGP. The catalytic alphaGlu49 rotates to interact with the sp3-hybridized atom and the 3' hydroxyl group suggesting that it serves both as proton donor and acceptor in the alpha-reaction. The second catalytic residue, alphaAsp60 interacts with the atom corresponding to the indolyl nitrogen, and the catalytically important loop alphaL6 is in the closed, high activity conformation. Comparison of the TSA and TSA-transition state analogue structures with the crystal structure of BX1 suggests that the faster catalytic rate of BX1 may be due to a stabilization of the active conformation: loop alphaL6 is closed and the catalytic glutamate is in the active conformation. The latter is caused by a substitution of the residues that stabilize the inactive conformation in TRPS. SN - 0022-2836 UR - https://www.unboundmedicine.com/medline/citation/16120446/On_the_structural_basis_of_the_catalytic_mechanism_and_the_regulation_of_the_alpha_subunit_of_tryptophan_synthase_from_Salmonella_typhimurium_and_BX1_from_maize_two_evolutionarily_related_enzymes_ DB - PRIME DP - Unbound Medicine ER -