1stq
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Cyrstal Structure of Cytochrome c Peroxidase Mutant: CcPK2M3
OverviewOverview
Previously a K(+)-binding site, analogous to that found in ascorbate, peroxidase (APX), was engineered into cytochrome c peroxidase (CcP) to, test the hypothesis that the bound K(+) influences the stability of the, Trp191 cation radical formed during the CcP catalytic cycle (Bonagura et, al., (1996) Biochemistry 35, 6107 and Bonagura et al., (1999) Biochemistry, 38, 5528). Characterization of this mutant, designated CcPK2, showed that, the stability of the Trp191 cation radical is dependent on the occupancy, of the engineered K(+) site and that the Trp191 radical was much less, stable in this mutant than in wild-type CcP. The mutations Met230Leu, Met231Gln, and Met172Ser have now been constructed on the CcPK2 mutant, template to test if the Met residues also contribute to the stabilization, of the Trp191 cation radical. Crystal structures show that the mutations, affect only the local structure near the sites of mutation. Removal of, these electronegative residues located less than 8 A from the Trp radical, results in a further destabilization of the Trp radical. The, characteristic EPR signal associated with the Trp radical is significantly, narrowed and is characteristic of a tyrosine radical signal. Double-mixing, stopped-flow experiments, where the delay time between the formation of, CcP compound I and its mixing with horse heart ferrocytochrome c is, varied, show that the stability of the Trp radical decreases as the Met, residues are removed from the proximal cavity. When taken together, these, results demonstrate a strong correlation between the experimentally, determined stability of the Trp191 radical, the enzyme activity, and the, calculated electrostatic stabilization of the Trp191 radical.
About this StructureAbout this Structure
1STQ is a Single protein structure of sequence from Saccharomyces cerevisiae with K and HEM as ligands. Active as Cytochrome-c peroxidase, with EC number 1.11.1.5 Full crystallographic information is available from OCA.
ReferenceReference
Electrostatic control of the tryptophan radical in cytochrome c peroxidase., Barrows TP, Bhaskar B, Poulos TL, Biochemistry. 2004 Jul 13;43(27):8826-34. PMID:15236591
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