2j9z: Difference between revisions

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[[Image:2j9z.jpg|left|200px]]
{{Seed}}
[[Image:2j9z.png|left|200px]]


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{{STRUCTURE_2j9z|  PDB=2j9z  |  SCENE=  }}  
{{STRUCTURE_2j9z|  PDB=2j9z  |  SCENE=  }}  


'''TRYPTOPHAN SYNTHASE T110 MUTANT COMPLEX'''
===TRYPTOPHAN SYNTHASE T110 MUTANT COMPLEX===




==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 --&gt; Val, and betaGln114 --&gt; 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.
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{{ABSTRACT_PUBMED_18004874}}


==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]]
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Revision as of 17:58, 27 July 2008

File:2j9z.png

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

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