2EZ1: Holo Tyrosine Phenol-lyase From Citrobacter Freundii At Ph 8.0

Tyrosine phenol-lyase, a tetrameric pyridoxal 5'-phosphate dependent enzyme, catalyzes the reversible hydrolytic cleavage of L-tyrosine to phenol and ammonium pyruvate. Here we describe the crystal structure of the Citrobacter freundii holoenzyme at 1.9 A resolution. The structure reveals a network of protein interactions with the cofactor, pyridoxal 5'-phosphate, and details of coordination of the catalytically important K+ ion. We also present the structure of the apoenzyme at 1.85 A resolution. Both structures were determined using crystals grown at pH 8.0, which is close to the pH of the maximal enzymatic activity (8.2). Comparison of the apoenzyme structure with the one previously determined at pH 6.0 reveals significant differences. The data suggest that the decrease of the enzymatic activity at pH 6.0 may be caused by conformational changes in the active site residues Tyr71, Tyr291, and Arg381 and in the monovalent cation binding residue Glu69. Moreover, at pH 8.0 we observe two different active site conformations: open, which was characterized before, and closed, which is observed for the first time in beta-eliminating lyases. In the closed conformation a significant part of the small domain undergoes an extraordinary motion of up to 12 A toward the large domain, closing the active site cleft and bringing the catalytically important Arg381 and Phe448 into the active site. The closed conformation allows rationalization of the results of previous mutational studies and suggests that the observed active site closure is critical for the course of the enzymatic reaction and for the enzyme's specificity toward its physiological substrate. Finally, the closed conformation allows us to model keto(imino)quinonoid, the key transition intermediate.
PDB ID: 2EZ1Download
MMDB ID: 40386
PDB Deposition Date: 2005/11/10
Updated in MMDB: 2017/10
Experimental Method:
x-ray diffraction
Resolution: 1.9  Å
Source Organism:
Similar Structures:
Biological Unit for 2EZ1: tetrameric; determined by author and by software (PISA,PQS)
Molecular Components in 2EZ1
Label Count Molecule
Proteins (4 molecules)
Tyrosine Phenol-lyase
Molecule annotation
Chemicals (4 molecules)
* Click molecule labels to explore molecular sequence information.

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