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| - | [[Image:2j9z.jpg|left|200px]] | + | {{Seed}} |
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| | {{STRUCTURE_2j9z| PDB=2j9z | SCENE= }} | | {{STRUCTURE_2j9z| PDB=2j9z | SCENE= }} |
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| - | '''TRYPTOPHAN SYNTHASE T110 MUTANT COMPLEX'''
| + | ===TRYPTOPHAN SYNTHASE T110 MUTANT COMPLEX=== |
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| - | ==Overview==
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| - | In the PLP-requiring alpha2beta2 tryptophan synthase complex, recognition of the substrate l-Ser at the beta-site includes a loop structure (residues beta110-115) extensively H-bonded to the substrate alpha-carboxylate. To investigate the relationship of this subsite to catalytic function and to the regulation of substrate channeling, two loop mutants were constructed: betaThr110 --> Val, and betaGln114 --> Asn. The betaT110V mutation greatly impairs both catalytic activity in the beta-reaction, and allosteric communication between the alpha- and beta-sites. The crystal structure of the betaT110V mutant shows that the modified l-Ser carboxylate subsite has altered protein interactions that impair beta-site catalysis and the communication of allosteric signals between the alpha- and beta-sites. Purified betaQ114N consists of two species of mutant protein, one with a reddish color (lambdamax = 506 nm). The reddish species is unable to react with l-Ser. The second betaQ114N species displays significant catalytic activities; however, intermediates obtained on reaction with substrate l-Ser and substrate analogues exhibit perturbed UV/vis absorption spectra. Incubation with l-Ser results in the formation of an inactive species during the first 15 min with lambdamax approximately 320 nm, followed by a slower conversion over 24 h to the species with lambdamax = 506 nm. The 320 and 506 nm species originate from conversion of the alpha-aminoacrylate external aldimine to the internal aldimine and alpha-aminoacrylate, followed by the nucleophilic attack of alpha-aminoacrylate on C-4' of the internal aldimine to give a covalent adduct with PLP. Subsequent treatment with sodium hydroxide releases a modified coenzyme consisting of a vinylglyoxylic acid moiety linked through C-4' to the 4-position of the pyridine ring. We conclude that the shortening of the side chain accompanying the replacement of beta114-Gln by Asn relaxes the steric constraints that prevent this reaction in the wild-type enzyme. This study reveals a new layer of structure-function interactions essential for reaction specificity in tryptophan synthase.
| + | The line below this paragraph, {{ABSTRACT_PUBMED_18004874}}, adds the Publication Abstract to the page |
| | + | (as it appears on PubMed at http://www.pubmed.gov), where 18004874 is the PubMed ID number. |
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| | + | {{ABSTRACT_PUBMED_18004874}} |
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| | ==About this Structure== | | ==About this Structure== |
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| | [[Category: Synthase carbon- oxygen lyase]] | | [[Category: Synthase carbon- oxygen lyase]] |
| | [[Category: Tryptophan biosynthesis]] | | [[Category: Tryptophan biosynthesis]] |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun May 4 08:34:42 2008'' | + | |
| | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Jul 27 20:58:35 2008'' |
Revision as of 17:58, 27 July 2008
Template:STRUCTURE 2j9z
TRYPTOPHAN SYNTHASE T110 MUTANT COMPLEX
Template:ABSTRACT PUBMED 18004874
About this Structure
2J9Z is a Protein complex structure of sequences from Salmonella typhimurium. Full crystallographic information is available from OCA.
Reference
BetaQ114N and betaT110V mutations reveal a critically important role of the substrate alpha-carboxylate site in the reaction specificity of tryptophan synthase., Blumenstein L, Domratcheva T, Niks D, Ngo H, Seidel R, Dunn MF, Schlichting I, Biochemistry. 2007 Dec 11;46(49):14100-16. Epub 2007 Nov 16. PMID:18004874
Page seeded by OCA on Sun Jul 27 20:58:35 2008
