title: Mutation-Induced Changes in the Protein Environment and Site Energies in the (M)L214G Mutant of the Rhodobacter sphaeroides Bacterial Reaction Center.
abstract: This work focuses on the low-temperature (5 K) photochemical (transient) hole-burned (HB) spectra within the P870 absorption band, and their theoretical analysis, for the (M)L214G mutant of the photosynthetic Rhodobacter sphaeroides bacterial reaction center (bRC). To provide insight into system-bath interactions of the bacteriochlorophyll a (BChl a) special pair, i.e., P870, in the mutated bRC, the optical line shape function for the P870 band is calculated numerically. On the basis of the modeling studies, we demonstrate that (M)L214G mutation leads to a heterogeneous population of bRCs with modified (increased) total electron-phonon coupling strength of the special pair BChl a and larger inhomogeneous broadening. Specifically, we show that after mutation in the (M)L214G bRC a large fraction (∼50%) of the bacteriopheophytin (HA) chromophores shifts red and the 800 nm absorption band broadens, while the remaining fraction of HA cofactors retains nearly the same site energy as HA in the wild-type bRC. Modeling using these two subpopulations allowed for fits of the absorption and nonresonant (transient) HB spectra of the mutant bRC in the charge neutral, oxidized, and charge-separated states using the Frenkel exciton Hamiltonian, providing new insight into the mutant's complex electronic structure. Although the average (M)L214G mutant quantum efficiency of P(+)QA(-) state formation seems to be altered in comparison with the wild-type bRC, the average electron transfer time (measured via resonant transient HB spectra within the P870 band) was not affected. Thus, mutation in the vicinity of the electron acceptor (HA) does not tune the charge separation dynamics. Finally, quenching of the (M)L214G mutant excited states by P(+) is addressed by persistent HB spectra burned within the B band in chemically oxidized samples.
authors.forename: Ryszard
authors.initials: R
authors.lastname: Jankowiak
authors.affiliation: Department of Theoretical Physics, Vilnius University , 10222 Vilnius, Lithuania.
authors.forename: Olga
authors.initials: O
authors.lastname: Rancova
authors.forename: Jinhai
authors.initials: J
authors.lastname: Chen
authors.forename: Adam
authors.initials: A
authors.lastname: Kell
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia , Vancouver, BC V6T 1Z3, Canada.
authors.forename: Rafael G
authors.initials: RG
authors.lastname: Saer
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia , Vancouver, BC V6T 1Z3, Canada.
authors.forename: J Thomas
authors.initials: JT
authors.lastname: Beatty
authors.affiliation: Department of Theoretical Physics, Vilnius University , 10222 Vilnius, Lithuania.
authors.forename: Darius
authors.initials: D
authors.lastname: Abramavicius
mesh_terms: D003198:Computer Simulation; D004583:Electrons; D005292:Ferricyanides / Q000737:chemistry; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010084:Oxidation-Reduction; D010674:Pheophytins / Q000737:chemistry / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011522:Protons; D011789:Quantum Theory; D012242:Rhodobacter sphaeroides / Q000737:chemistry* / Q000235:genetics; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: D005292:Ferricyanides; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; D011522:Protons; C007931:hexacyanoferrate III; C006678:bacteriopheophytin