Significantly shorter Fe–S bond in cytochrome P450-I is consistent with greater reactivity relative to chloroperoxidase

• Published in: Nature chemistry 2015-09, Vol.7 (9), p.696-702
• Main Authors: Krest, Courtney M., Silakov, Alexey, Rittle, Jonathan, Yosca, Timothy H., Onderko, Elizabeth L., Calixto, Julio C., Green, Michael T.
• Format: Article
• Language: English
• Subjects: 639/638/45/49/1141; 639/638/45/603; 639/638/77/603; Analytical Chemistry; Archaeal Proteins - chemistry; Archaeal Proteins - genetics; Archaeal Proteins - metabolism; BASIC BIOLOGICAL SCIENCES; Biocatalysis; Biochemistry; Carbon - chemistry; Chemistry; Chemistry/Food Science; Chloride Peroxidase - chemistry; Chloride Peroxidase - metabolism; Cytochrome; Cytochrome P-450 Enzyme System - chemistry; Cytochrome P-450 Enzyme System - genetics; Cytochrome P-450 Enzyme System - metabolism; Electron Spin Resonance Spectroscopy; Enzymes; Fatty acids; Fungi - enzymology; Hydrocarbons; Hydrogen; Hydrogen - chemistry; Hydrogen Bonding; Hydrogen bonds; Inorganic Chemistry; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Iron - chemistry; Kinetics; Ligands; metalloproteins; Organic Chemistry; Oxidation-Reduction; Physical Chemistry; Recombinant Proteins - biosynthesis; Recombinant Proteins - chemistry; Recombinant Proteins - isolation & purification; Spectroscopy, Mossbauer; Sulfolobus acidocaldarius - metabolism; Sulfur - chemistry; Temperature
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/nchem.2306

Cytochrome P450 (P450) and chloroperoxidase (CPO) are thiolate-ligated haem proteins that catalyse the activation of carbon hydrogen bonds. The principal intermediate in these reactions is a ferryl radical species called compound I. P450 compound I (P450-I) is significantly more reactive than CPO-I, which only cleaves activated C–H bonds. To provide insight into the differing reactivities of these intermediates, we examined CPO-I and P450-I using variable-temperature Mössbauer and X-ray absorption spectroscopies. These measurements indicate that the Fe–S bond is significantly shorter in P450-I than in CPO-I. This difference in Fe–S bond lengths can be understood in terms of variations in the hydrogen-bonding patterns within the ‘cys-pocket’ (a portion of the proximal helix that encircles the thiolate ligand). Weaker hydrogen bonding in P450-I results in a shorter Fe–S bond, which enables greater electron donation from the axial thiolate ligand. This observation may in part explain P450's greater propensity for C–H bond activation. Cytochrome P450 (P450) and chloroperoxidase (CPO) are both thiolate-ligated haem proteins that form a ferryl radical species called compound I. P450-I is, however, significantly more reactive than CPO-I. Variable-temperature Mössbauer and X-ray absorption measurements have now shown that increased electron donation from the axial thiolate ligand in P450-I may explain its greater propensity for C–H bond activation.