2hrw
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(New page: 200px<br /><applet load="2hrw" size="350" color="white" frame="true" align="right" spinBox="true" caption="2hrw, resolution 2.200Å" /> '''Crystal Structure o...)
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Revision as of 18:27, 29 January 2008
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Crystal Structure of Phosphonopyruvate Hydrolase
Overview
Phosphonopyruvate (P-pyr) hydrolase (PPH), a member of the, phosphoenolpyruvate (PEP) mutase/isocitrate lyase (PEPM/ICL) superfamily, hydrolyzes P-pyr and shares the highest sequence identity and functional, similarity with PEPM. Recombinant PPH from Variovorax sp. Pal2 was, expressed in Escherichia coli and purified to homogeneity. Analytical gel, filtration indicated that the protein exists in solution predominantly as, a tetramer. The PPH pH rate profile indicates maximal activity over a, broad pH range. The steady-state kinetic constants determined for a rapid, equilibrium ordered kinetic mechanism with Mg2+ binding first (Kd = 140, +/- 40 microM), are kcat = 105 +/- 2 s(-1) and P-pyr Km = 5 +/- 1 microM., PEP (slow substrate kcat = 2 x 10(-4) s(-1)), oxalate, and sulfopyruvate, are competitive inhibitors with Ki values of 2.0 +/- 0.1 mM, 17 +/- 1, microM, and 210 +/- 10 microM, respectively. Three PPH crystal structures, have been determined, that of a ligand-free enzyme, the enzyme bound to, Mg2+ and oxalate (inhibitor), and the enzyme bound to Mg2+ and P-pyr, (substrate). The complex with the inhibitor was obtained by, cocrystallization, whereas that with the substrate was obtained by briefly, soaking crystals of the ligand-free enzyme with P-pyr prior to flash, cooling. The PPH structure resembles that of the other members of the, PEPM/ICL superfamily and is most similar to the functionally related, enzyme, PEPM. Each monomer of the dimer of dimers exhibits an, (alpha/beta)8 barrel fold with the eighth helix swapped between two, molecules of the dimer. Both P-pyr and oxalate are anchored to the active, site by Mg2+. The loop capping the active site is disordered in all three, structures, in contrast to PEPM, where the equivalent loop adopts an open, or disordered conformation in the unbound state but sequesters the, inhibitor from solvent in the bound state. Crystal packing may have, favored the open conformation of PPH even when the enzyme was, cocrystallized with the oxalate inhibitor. Structure alignment of PPH with, other superfamily members revealed two pairs of invariant or, conservatively replaced residues that anchor the flexible gating loop. The, proposed PPH catalytic mechanism is analogous to that of PEPM but includes, activation of a water nucleophile with the loop Thr118 residue.
About this Structure
2HRW is a Single protein structure of sequence from Variovorax sp. pal2 with and as ligands. Full crystallographic information is available from OCA.
Reference
Structure and kinetics of phosphonopyruvate hydrolase from Variovorax sp. Pal2: new insight into the divergence of catalysis within the PEP mutase/isocitrate lyase superfamily., Chen CC, Han Y, Niu W, Kulakova AN, Howard A, Quinn JP, Dunaway-Mariano D, Herzberg O, Biochemistry. 2006 Sep 26;45(38):11491-504. PMID:16981709
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