PMID: 25076049

Authors:

Bhagi-Damodaran A, Petrik ID, Marshall NM, Robinson H, Lu Y

Title:

Systematic Tuning of Heme Redox Potentials and its Effects on O Reduction Rates in a Designed Oxidase in Myoglobin.

Journal:

J Am Chem Soc. 2014 Jul 30.

Abstract:

Cytochrome c Oxidase (CcO) is known to catalyze the reduction of O2 to H2O efficiently with a much lower overpotential than almost all other O2 reduction catalysts. However, the methods by which the enzyme fine-tunes the reduction potential (E degrees ) of its active site and its influence on the O2 reduction activity are not well understood. In this work, we report systematic tuning of the heme E degrees in a functional model of CcO in myoglobin containing three histidines and one tyrosine in the distal pocket of heme. By removing H-bonding interactions between Ser92, and the proximal His ligand through Ser92Ala mutation, we have increased the heme E degrees from 95 +/- 2 mV to 123 +/- 3 mV . Additionally, replacing the native heme b in the protein with heme a analogs, diacetyl, monoformyl and diformyl heme, resulted in an E degrees value of 175 +/- 5 mV, 210 +/- 6 mV and 320 +/- 10 mV, respectively. Interestingly, a strong enhancement of the O2 reduction activity was observed with increasing heme E degrees . The methods of tuning the heme E degrees through a combination of secondary sphere mutations and heme substitutions can be applied to tune E degrees of other heme proteins, allowing for comprehensive investigations of the relationship between E degrees and enzymatic activity.