The CO Photodissociation and Recombination Dynamics of the W172Y/F282T Ligand Channel Mutant of Rhodobacter sphaeroides aa3 Cytochrome c Oxidase. (21st April 2016) - Cassano, Jennifer A.
Abstract: In the ligand channel of the cytochrome c oxidase from Rhodobacter sphaeroides ( Rs aa 3 ) W172 and F282 have been proposed to generate a constriction that may slow ligand access to and from the active site. To explore this issue, the tryptophan and phenylalanine residues in Rs aa 3 were mutated to the less bulky tyrosine and threonine residues, respectively, which occupy these sites in Thermus thermophilus ( Tt ) ba 3 cytochrome oxidase. The CO photolysis and recombination dynamics of the reduced wild‐type Rs aa 3 and the W172Y/F282T mutant were investigated using time‐resolved optical absorption spectroscopy. The spectral changes associated with the multiple processes are attributed to different conformers. The major CO recombination process (44 μs) in the W172Y/F282T mutant is ~500 times faster than the predominant CO recombination process in the wild‐type enzyme (~23 ms). Classical dynamic simulations of the wild‐type enzyme and double mutant showed significant structural changes at the active site in the mutant, including movement of the heme a 3 ring‐D propionate toward CuB and reduced binuclear center cavity volume. These structural changes effectively close the ligand exit pathway from the binuclear center, providing a basis for the faster CO recombination in the double mutant. Abstract : We investigated the effect of mutating the tryptophan and phenylalanine residues that define the narrowing of the ligand channel in Rhodobacter sphaeroides aa 3 to the less bulky tyrosine and threonine, respectively. Our time‐resolved optical absorption results show that the major CO recombination process in the mutant (44 μs) is 500 times faster than in the wild type (~23 ms). Classical molecular dynamics simulations of the double mutant show significant changes at the active site that effectively close the ligand exit pathway from the binuclear center, providing a structural basis for the faster CO recombination in the double mutant.