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Light-Induced Nanosecond Relaxation Dynamics of Rhenium-Labelled Pseudomonas Aeruginosa Azurins.

07:00 EST 14th January 2020 | BioPortfolio

Summary of "Light-Induced Nanosecond Relaxation Dynamics of Rhenium-Labelled Pseudomonas Aeruginosa Azurins."

Time-resolved phosphorescence spectra of Re(CO)3(dmp)+ and Re(CO)3(phen)+ chromophores (dmp = 4,7-dimethyl-1,10-phenanthroline, phen = 1,10-phenanthroline) bound to surface histidines (H83, H124, H126) of Pseudomonas aeruginosa azurin mutants exhibit dynamic band maxima shifts to lower wavenumbers following 3-exponential kinetics with 1-5 and 20-100 ns major phases, and a 1.1-2.5 s minor (5-16%) phase. Observation of slow relaxation components was made possible by using an organometallic Re chromophore as a probe whose long phosphorescence lifetime extends the observation window up to ~3 s. Integrated emission-band areas also decay with 2- or 3-exponential kinetics; the faster decay phase(s) are relaxation-related, whereas the slowest one (360-680 ns (dmp); 90-140 ns (phen)) arises mainly from population decay. As a result of shifting bands, the emission intensity decay kinetics depend on the detection wavelength. Detailed kinetics analyses and comparisons with band-shift dynamics are needed to disentangle relaxation and population decay kinetics if they occur on comparable timescales. The dynamic phosphorescence Stokes shift in Re-azurins is caused by relaxation motions of the solvent, the protein and solvated amino acid side chains at the Re binding site in response to chromophore electronic excitation. Comparing relaxation and decay kinetics of Re(dmp)124K122CuII and Re(dmp)124W122CuII suggests that ET and relaxation motions in the W122 mutant are coupled. It follows that nanosecond and faster photoinduced ET steps in azurins (and, likely other redox proteins) occur from unrelaxed systems; importantly, these reactions can be driven (or hindered) by structural and solvational dynamics.

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Name: The journal of physical chemistry. B
ISSN: 1520-5207
Pages:

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