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Two Tryptophans Are Better Than One in Accelerating Electron Flow through a Protein

Takematsu, Kana and Williamson, Heather R. and Nikolovski, Pavle and Kaiser, Jens T. and Sheng, Yuling and Pospíšil, Petr and Towrie, Michael and Heyda, Jan and Hollas, Daniel and Záliš, Stanislav and Gray, Harry B. and Vlček, Antonín and Winkler, Jay R. (2019) Two Tryptophans Are Better Than One in Accelerating Electron Flow through a Protein. ACS Central Science, 5 (1). pp. 192-200. ISSN 2374-7943. PMCID PMC6346393. doi:10.1021/acscentsci.8b00882.

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We have constructed and structurally characterized a Pseudomonas aeruginosa azurin mutant Re126WWCu^I, where two adjacent tryptophan residues (W124 and W122, indole separation 3.6–4.1 Å) are inserted between the Cu^I center and a Re photosensitizer coordinated to the imidazole of H126 (Re^I(H126)(CO)_3(4,7-dimethyl-1,10-phenanthroline)^+). Cu^I oxidation by the photoexcited Re label (*Re) 22.9 Å away proceeds with a ∼70 ns time constant, similar to that of a single-tryptophan mutant (∼40 ns) with a 19.4 Å Re–Cu distance. Time-resolved spectroscopy (luminescence, visible and IR absorption) revealed two rapid reversible electron transfer steps, W124 → *Re (400–475 ps, K_1 ≅ 3.5–4) and W122 → W124•^+ (7–9 ns, K_2 ≅ 0.55–0.75), followed by a rate-determining (70–90 ns) Cu^I oxidation by W122•^+ ca. 11 Å away. The photocycle is completed by 120 μs recombination. No photochemical Cu^I oxidation was observed in Re126FWCu^I, whereas in Re126WFCu^I, the photocycle is restricted to the ReH126W124 unit and Cu^I remains isolated. QM/MM/MD simulations of Re126WWCu^I indicate that indole solvation changes through the hopping process and W124 → *Re electron transfer is accompanied by water fluctuations that tighten W124 solvation. Our finding that multistep tunneling (hopping) confers a ∼9000-fold advantage over single-step tunneling in the double-tryptophan protein supports the proposal that hole-hopping through tryptophan/tyrosine chains protects enzymes from oxidative damage.

Item Type:Article
Related URLs:
URLURL TypeDescription Information CentralArticle
Takematsu, Kana0000-0002-2334-336X
Williamson, Heather R.0000-0002-2413-659X
Kaiser, Jens T.0000-0002-5948-5212
Heyda, Jan0000-0002-9428-9508
Hollas, Daniel0000-0003-4075-6438
Gray, Harry B.0000-0002-7937-7876
Vlček, Antonín0000-0002-6413-8311
Winkler, Jay R.0000-0002-4453-9716
Additional Information:© 2018 American Chemical Society. This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Received: November 30, 2018; Published: January 7, 2019. We thank Martin Pižl (JH Institute) for his help analyzing the TRIR spectra. Research reported in this publication was supported by 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. Additional support was provided by the Arnold and Mabel Beckman Foundation, the Czech Science Foundation (GAČR) Grant 17-011375, and the STFC Rutherford Appleton Laboratory (UK). X-ray crystallography data were collected on SSRL Beamline 12-2 through the support of the Caltech Molecular Observatory, funded by the Gordon and Betty Moore Foundation, Beckman Institute, and the Sanofi-Aventis Bioengineering Research Program. Operations at SSRL are supported by U.S. DOE and NIH. The authors declare no competing financial interest. Safety Statement: No unexpected or unusually high safety hazards were encountered.
Funding AgencyGrant Number
Arnold and Mabel Beckman FoundationUNSPECIFIED
Czech Science Foundation17-011375
Science and Technology Facilities Council (STFC)UNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Caltech Beckman InstituteUNSPECIFIED
Sanofi-Aventis Bioengineering Research ProgramUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Issue or Number:1
PubMed Central ID:PMC6346393
Record Number:CaltechAUTHORS:20190108-080959942
Persistent URL:
Official Citation:Two Tryptophans Are Better Than One in Accelerating Electron Flow through a Protein. Kana Takematsu, Heather R Williamson, Pavle Nikolovski, Jens T. Kaiser, Yuling Sheng, Petr Pospíšil, Michael Towrie, Jan Heyda, Daniel Hollas, Stanislav Záliš, Harry B. Gray, Antonín Vlček, and Jay R. Winkler. ACS Central Science 2019 5 (1), 192-200. DOI: 10.1021/acscentsci.8b00882
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92125
Deposited By: Tony Diaz
Deposited On:08 Jan 2019 16:26
Last Modified:24 Feb 2022 17:55

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