2cll: Difference between revisions
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==Overview== | ==Overview== | ||
In the tryptophan synthase bienzyme complex, indole produced by substrate cleavage at the alpha-site is channeled to the beta-site via a 25 A long tunnel. Within the beta-site, indole and l-Ser react with pyridoxal 5'-phosphate in a two-stage reaction to give l-Trp. In stage I, l-Ser forms an external aldimine, E(Aex1), which converts to the alpha-aminoacrylate aldimine, E(A-A). Formation of E(A-A) at the beta-site activates the alpha-site >30-fold. In stage II, indole reacts with E(A-A) to give l-Trp. The binding of alpha-site ligands (ASLs) exerts strong allosteric effects on the reaction of substrates at the beta-site: the distribution of intermediates formed in stage I is shifted in favor of E(A-A), and the binding of ASLs triggers a conformational change in the beta-site to a state with an increased affinity for l-Ser. Here, we compare the behavior of new ASLs as allosteric effectors of stage I with the behavior of the natural product, d-glyceraldehyde 3-phosphate. Rapid kinetics and kinetic isotope effects show these ASLs bind with affinities ranging from micro- to millimolar, and the rate-determining step for conversion of E(Aex1) to E(A-A) is increased by 8-10-fold. To derive a structure-based mechanism for stage I, X-ray structures of both the E(Aex1) and E(A-A) states complexed with the different ASLs were determined and compared with structures of the ASL complexes with the internal aldimine [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) Biochemistry 46, 7713-7727]. | |||
==About this Structure== | ==About this Structure== | ||
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==Reference== | ==Reference== | ||
Allosteric regulation of substrate channeling in tryptophan synthase: modulation of the L-serine reaction in stage I of the beta-reaction by alpha-site ligands., Ngo H, Kimmich N, Harris R, Niks D, Blumenstein L, Kulik V, Barends TR, Schlichting I, Dunn MF, Biochemistry. 2007 Jul 3;46(26):7740-53. Epub 2007 Jun 9. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/17559232 17559232] | |||
[[Category: Protein complex]] | [[Category: Protein complex]] | ||
[[Category: Salmonella typhimurium]] | [[Category: Salmonella typhimurium]] | ||
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[[Category: Pyridoxal phosphate]] | [[Category: Pyridoxal phosphate]] | ||
[[Category: Tryptophan biosynthesis]] | [[Category: Tryptophan biosynthesis]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Wed May 14 11:37:29 2008'' | ||
Revision as of 08:37, 14 May 2008
TRYPTOPHAN SYNTHASE (EXTERNAL ALDIMINE STATE) IN COMPLEX WITH N-(4'-TRIFLUOROMETHOXYBENZENESULFONYL)-2-AMINO-1-ETHYLPHOSPHATE (F9)
Overview
In the tryptophan synthase bienzyme complex, indole produced by substrate cleavage at the alpha-site is channeled to the beta-site via a 25 A long tunnel. Within the beta-site, indole and l-Ser react with pyridoxal 5'-phosphate in a two-stage reaction to give l-Trp. In stage I, l-Ser forms an external aldimine, E(Aex1), which converts to the alpha-aminoacrylate aldimine, E(A-A). Formation of E(A-A) at the beta-site activates the alpha-site >30-fold. In stage II, indole reacts with E(A-A) to give l-Trp. The binding of alpha-site ligands (ASLs) exerts strong allosteric effects on the reaction of substrates at the beta-site: the distribution of intermediates formed in stage I is shifted in favor of E(A-A), and the binding of ASLs triggers a conformational change in the beta-site to a state with an increased affinity for l-Ser. Here, we compare the behavior of new ASLs as allosteric effectors of stage I with the behavior of the natural product, d-glyceraldehyde 3-phosphate. Rapid kinetics and kinetic isotope effects show these ASLs bind with affinities ranging from micro- to millimolar, and the rate-determining step for conversion of E(Aex1) to E(A-A) is increased by 8-10-fold. To derive a structure-based mechanism for stage I, X-ray structures of both the E(Aex1) and E(A-A) states complexed with the different ASLs were determined and compared with structures of the ASL complexes with the internal aldimine [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) Biochemistry 46, 7713-7727].
About this Structure
2CLL is a Protein complex structure of sequences from Salmonella typhimurium. Full crystallographic information is available from OCA.
Reference
Allosteric regulation of substrate channeling in tryptophan synthase: modulation of the L-serine reaction in stage I of the beta-reaction by alpha-site ligands., Ngo H, Kimmich N, Harris R, Niks D, Blumenstein L, Kulik V, Barends TR, Schlichting I, Dunn MF, Biochemistry. 2007 Jul 3;46(26):7740-53. Epub 2007 Jun 9. PMID:17559232 Page seeded by OCA on Wed May 14 11:37:29 2008
Proteopedia Page Contributors and Editors (what is this?)
- Pages with broken file links
- Protein complex
- Salmonella typhimurium
- Tryptophan synthase
- Barends, T R.
- Blumenstein, L.
- Dunn, M F.
- Harris, R.
- Kimmich, N.
- Kulik, V.
- Ngo, H.
- Niks, D.
- Schlichting, I.
- Allosteric enzyme
- Amino-acid biosynthesis
- Aromatic amino acid biosynthesis
- Carbon-oxygen lyase
- Lyase
- Pyridoxal phosphate
- Tryptophan biosynthesis
