1jx0
From Proteopedia
| Line 1: | Line 1: | ||
[[Image:1jx0.gif|left|200px]] | [[Image:1jx0.gif|left|200px]] | ||
| - | + | <!-- | |
| - | + | The line below this paragraph, containing "STRUCTURE_1jx0", creates the "Structure Box" on the page. | |
| - | + | You may change the PDB parameter (which sets the PDB file loaded into the applet) | |
| - | + | or the SCENE parameter (which sets the initial scene displayed when the page is loaded), | |
| - | + | or leave the SCENE parameter empty for the default display. | |
| - | | | + | --> |
| - | | | + | {{STRUCTURE_1jx0| PDB=1jx0 | SCENE= }} |
| - | + | ||
| - | + | ||
| - | }} | + | |
'''Chalcone Isomerase--Y106F mutant''' | '''Chalcone Isomerase--Y106F mutant''' | ||
| Line 29: | Line 26: | ||
[[Category: Jez, J M.]] | [[Category: Jez, J M.]] | ||
[[Category: Noel, J P.]] | [[Category: Noel, J P.]] | ||
| - | [[Category: | + | [[Category: Monomer]] |
| - | [[Category: | + | [[Category: Unique fold]] |
| - | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 22:01:42 2008'' | |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | + | |
Revision as of 19:01, 2 May 2008
Chalcone Isomerase--Y106F mutant
Overview
In flavonoid, isoflavonoid, and anthocyanin biosynthesis, chalcone isomerase (CHI) catalyzes the intramolecular cyclization of chalcones into (S)-flavanones with a second-order rate constant that approaches the diffusion-controlled limit. The three-dimensional structures of alfalfa CHI complexed with different flavanones indicate that two sets of hydrogen bonds may possess critical roles in catalysis. The first set of interactions includes two conserved amino acids (Thr48 and Tyr106) that mediate a hydrogen bond network with two active site water molecules. The second set of hydrogen bonds occurs between the flavanone 7-hydroxyl group and two active site residues (Asn113 and Thr190). Comparison of the steady-state kinetic parameters of wild-type and mutant CHIs demonstrates that efficient cyclization of various chalcones into their respective flavanones requires both sets of contacts. For example, the T48A, T48S, Y106F, N113A, and T190A mutants exhibit 1550-, 3-, 30-, 7-, and 6-fold reductions in k(cat) and 2-3-fold changes in K(m) with 4,2',4'-trihydroxychalcone as a substrate. Kinetic comparisons of the pH-dependence of the reactions catalyzed by wild-type and mutant enzymes indicate that the active site hydrogen bonds contributed by these four residues do not significantly alter the pK(a) of the intramolecular cyclization reaction. Determinations of solvent kinetic isotope and solvent viscosity effects for wild-type and mutant enzymes reveal a change from a diffusion-controlled reaction to one limited by chemistry in the T48A and Y106F mutants. The X-ray crystal structures of the T48A and Y106F mutants support the assertion that the observed kinetic effects result from the loss of key hydrogen bonds at the CHI active site. Our results are consistent with a reaction mechanism for CHI in which Thr48 polarizes the ketone of the substrate and Tyr106 stabilizes a key catalytic water molecule. Hydrogen bonds contributed by Asn113 and Thr190 provide additional stabilization in the transition state. Conservation of these residues in CHIs from other plant species implies a common reaction mechanism for enzyme-catalyzed flavanone formation in all plants.
About this Structure
1JX0 is a Single protein structure of sequence from Medicago sativa. Full crystallographic information is available from OCA.
Reference
Role of hydrogen bonds in the reaction mechanism of chalcone isomerase., Jez JM, Bowman ME, Noel JP, Biochemistry. 2002 Apr 23;41(16):5168-76. PMID:11955065 Page seeded by OCA on Fri May 2 22:01:42 2008
