2ou4
From Proteopedia
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'''Crystal structure of D-tagatose 3-epimerase from Pseudomonas cichorii''' | '''Crystal structure of D-tagatose 3-epimerase from Pseudomonas cichorii''' | ||
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[[Category: Yamada, M.]] | [[Category: Yamada, M.]] | ||
[[Category: Yoshida, H.]] | [[Category: Yoshida, H.]] | ||
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| - | [[Category: | + | [[Category: Isomerase]] |
| - | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun May 4 11:39:28 2008'' | |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | + | |
Revision as of 08:39, 4 May 2008
Crystal structure of D-tagatose 3-epimerase from Pseudomonas cichorii
Overview
Pseudomonas cichoriiid-tagatose 3-epimerase (P. cichoriid-TE) can efficiently catalyze the epimerization of not only d-tagatose to d-sorbose, but also d-fructose to d-psicose, and is used for the production of d-psicose from d-fructose. The crystal structures of P. cichoriid-TE alone and in complexes with d-tagatose and d-fructose were determined at resolutions of 1.79, 2.28, and 2.06 A, respectively. A subunit of P. cichoriid-TE adopts a (beta/alpha)(8) barrel structure, and a metal ion (Mn(2+)) found in the active site is coordinated by Glu152, Asp185, His211, and Glu246 at the end of the beta-barrel. P. cichoriid-TE forms a stable dimer to give a favorable accessible surface for substrate binding on the front side of the dimer. The simulated omit map indicates that O2 and O3 of d-tagatose and/or d-fructose coordinate Mn(2+), and that C3-O3 is located between carboxyl groups of Glu152 and Glu246, supporting the previously proposed mechanism of deprotonation/protonation at C3 by two Glu residues. Although the electron density is poor at the 4-, 5-, and 6-positions of the substrates, substrate-enzyme interactions can be deduced from the significant electron density at O6. The O6 possibly interacts with Cys66 via hydrogen bonding, whereas O4 and O5 in d-tagatose and O4 in d-fructose do not undergo hydrogen bonding to the enzyme and are in a hydrophobic environment created by Phe7, Trp15, Trp113, and Phe248. Due to the lack of specific interactions between the enzyme and its substrates at the 4- and 5-positions, P. cichoriid-TE loosely recognizes substrates in this region, allowing it to efficiently catalyze the epimerization of d-tagatose and d-fructose (C4 epimer of d-tagatose) as well. Furthermore, a C3-O3 proton-exchange mechanism for P. cichoriid-TE is suggested by X-ray structural analysis, providing a clear explanation for the regulation of the ionization state of Glu152 and Glu246.
About this Structure
2OU4 is a Single protein structure of sequence from Pseudomonas cichorii. Full crystallographic information is available from OCA.
Reference
Crystal structures of D-tagatose 3-epimerase from Pseudomonas cichorii and its complexes with D-tagatose and D-fructose., Yoshida H, Yamada M, Nishitani T, Takada G, Izumori K, Kamitori S, J Mol Biol. 2007 Nov 23;374(2):443-53. Epub 2007 Sep 19. PMID:17936787 Page seeded by OCA on Sun May 4 11:39:28 2008
