title: Systematic tuning of heme redox potentials and its effects on O2 reduction rates in a designed oxidase in myoglobin.
abstract: Cytochrome c Oxidase (CcO) is known to catalyze the reduction of O2 to H2O efficiently with a much lower overpotential than most other O2 reduction catalysts. However, methods by which the enzyme fine-tunes the reduction potential (E°) of its active site and the corresponding influence on the O2 reduction activity are not well understood. In this work, we report systematic tuning of the heme E° in a functional model of CcO in myoglobin containing three histidines and one tyrosine in the distal pocket of heme. By removing hydrogen-bonding interactions between Ser92 and the proximal His ligand and a heme propionate, and increasing hydrophobicity of the heme pocket through Ser92Ala mutation, we have increased the heme E° from 95 ± 2 to 123 ± 3 mV. Additionally, replacing the native heme b in the CcO mimic with heme a analogs, diacetyl, monoformyl, and diformyl hemes, that posses electron-withdrawing groups, resulted in higher E° values of 175 ± 5, 210 ± 6, and 320 ± 10 mV, respectively. Furthermore, O2 consumption studies on these CcO mimics revealed a strong enhancement in O2 reduction rates with increasing heme E°. Such methods of tuning the heme E° through a combination of secondary sphere mutations and heme substitutions can be applied to tune E° of other heme proteins, allowing for comprehensive investigations of the relationship between E° and enzymatic activity.
authors: Department of Chemistry, University of Illinois, Urbana-Champaign , Urbana, Illinois 61801, United States.
authors: Ambika
authors: A
authors: Bhagi-Damodaran
authors: Igor D
authors: ID
authors: Petrik
authors: Nicholas M
authors: NM
authors: Marshall
authors: Howard
authors: H
authors: Robinson
authors: Yi
authors: Y
authors: Lu
mesh_terms: D000409:Alanine / Q000235:genetics; D000818:Animals; D001665:Binding Sites; D055162:Biocatalysis; D003300:Copper / Q000737:chemistry; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006639:Histidine / Q000235:genetics; D006860:Hydrogen Bonding; D008297:Male; D008958:Models, Molecular; D009211:Myoglobin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D015202:Protein Engineering; D012694:Serine / Q000235:genetics; D013094:Spermatozoa / Q000378:metabolism; D014907:Whales
chemical_list: D009211:Myoglobin; D006418:Heme; D012694:Serine; D006639:Histidine; D003300:Copper; D003576:Electron Transport Complex IV; D000409:Alanine; D010100:Oxygen