Light-Induced Nanosecond Relaxation Dynamics of Rhenium-Labeled Pseudomonas aeruginosa Azurins
Abstract
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, and 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 μs 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 μs. Integrated emission-band areas also decay with 2- or 3-exponential kinetics; the faster decay phase(s) is 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)124K122Cu^(II) and Re(dmp)124W122Cu^(II) suggests that electron transfer (ET) and relaxation motions in the W122 mutant are coupled. It follows that nanosecond and faster photo-induced 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.
Additional Information
© 2020 American Chemical Society. Received: November 18, 2019; Revised: January 2, 2020; Published: January 14, 2020. This work was supported by the Czech Science Foundation (GAČR) grant 17-011375, the Czech Ministry of Education (MŠMT) grant LTAUSA18026, the EPSRC grant (UK) EP/R029687/1, and the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under award number R01DK019038. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Yuling Sheng (Caltech) is acknowledged for her help with protein preparation. The authors declare no competing financial interest.Attached Files
Supplemental Material - jp9b10802_si_001.pdf
Files
Name | Size | Download all |
---|---|---|
md5:3e69af3a64a6f341360c578fb9f6a255
|
991.9 kB | Preview Download |
Additional details
- Eprint ID
- 100718
- DOI
- 10.1021/acs.jpcb.9b10802
- Resolver ID
- CaltechAUTHORS:20200114-133306708
- 17-011375
- Czech Science Foundation
- LTAUSA18026
- Ministerstvo Školství, Mládeže a Tělovýchovy
- EP/R029687/1
- Engineering and Physical Sciences Research Council (EPSRC)
- R01DK019038
- NIH
- Created
-
2020-01-14Created from EPrint's datestamp field
- Updated
-
2021-11-16Created from EPrint's last_modified field