Electron transfer (ET) between neutral and cationic tryptophan residues in the azurin construct [ReI(H126)(CO)3(dmp)](W124)(W122)CuI (dmp = 4,7-Me2-1,10-phenanthroline) was investigated by Born-Oppenheimer quantum-mechanics/molecular mechanics/molecular dynamics (QM/MM/MD) simulations. We focused on W124•+ ← W122 ET, which is the middle step of the photochemical hole-hopping process *ReII(CO)3(dmp•-) ← W124 ← W122 ← CuI, where sequential hopping amounts to nearly 10,000-fold acceleration over single-step tunneling (ACS Cent. Sci. 2019, 5, 192-200). In accordance with experiments, UKS-DFT QM/MM/MD simulations identified forward and reverse steps of W124•+ ↔ W122 ET equilibrium, as well as back ET ReI(CO)3(dmp•-) → W124•+ that restores *ReII(CO)3(dmp•-). Strong electronic coupling between the two indoles (≥40 meV in the crossing region) makes the productive W124•+ ← W122 ET adiabatic. Energies of the two redox states are driven to degeneracy by fluctuations of the electrostatic potential at the two indoles, mainly caused by water solvation, with contributions from the protein dynamics in the W122 vicinity. ET probability depends on the orientation of Re(CO)3(dmp) relative to W124 and its rotation diminishes the hopping yield. Comparison with hole hopping in natural systems reveals structural and dynamics factors that are important for designing efficient hole-hopping processes.

Beckman Institute California Institute of Technology Pasadena California 91125 United States

Department of Chemical Physics and Optics Faculty of Mathematics and Physics Charles University Ke Karlovu 3 CZ 121 16 Prague Czech Republic

Department of Chemistry Queen Mary University of London London E1 4NS U K

Department of Physical Chemistry University of Chemistry and Technology Prague Technická 5 CZ 166 28 Prague Czech Republic

J Heyrovský Institute of Physical Chemistry Czech Academy of Sciences Dolejškova 3 CZ 182 23 Prague Czech Republic

See more in PubMed

Gray H. B.; Winkler J. R. Functional and protective hole hopping in metalloenzymes. Chem. Sci. 2021, 12, 13988–14003. 10.1039/D1SC04286F. PubMed DOI PMC

Warren J. J.; Ener M. E.; Vlček A. Jr.; Winkler J. R.; Gray H. B. Electron hopping through proteins. Coord. Chem. Rev. 2012, 256, 2478–2487. 10.1016/j.ccr.2012.03.032. PubMed DOI PMC

Warren J. J.; Winkler J. R.; Gray H. B. Hopping maps for photosynthetic reaction centers. Coord. Chem. Rev. 2013, 257, 165–170. 10.1016/j.ccr.2012.07.002. PubMed DOI PMC

Winkler J. R.; Gray H. B. Electron Flow through Metalloproteins. Chem. Rev. 2014, 114, 3369–3380. 10.1021/cr4004715. PubMed DOI PMC

Olshansky L.; Greene B. L.; Finkbeiner C.; Stubbe J.; Nocera D. G. Photochemical Generation of a Tryptophan Radical within the Subunit Interface of Ribonucleotide Reductase. Biochemistry 2016, 55, 3234–3240. 10.1021/acs.biochem.6b00292. PubMed DOI PMC

Lukacs A.; Eker A. P. M.; Byrdin M.; Brettel K.; Vos M. H. Electron Hopping through the 15 Å Triple Tryptophan Molecular Wire in DNA Photolyase Occurs within 30 ps. J. Am. Chem. Soc. 2008, 130, 14394–14395. 10.1021/ja805261m. PubMed DOI

Byrdin M.; Lukacs A.; Thiagarajan V.; Eker A. P. M.; Brettel K.; Vos M. H. Quantum Yield Measurements of Short-Lived Photoactivation Intermediates in DNA Photolyase: Toward a Detailed Understanding of the Triple Tryptophan Electron Transfer Chain. J. Phys. Chem. A 2010, 114, 3207–3214. 10.1021/jp9093589. PubMed DOI

Liu Z.; Tan C.; Guo X.; Li J.; Wang L.; Sancar A.; Zhong D. Determining complete electron flow in the cofactor photoreduction of oxidized photolyase. Proc. Natl. Acad. Sci. U.S.A. 2013, 110, 12966–12971. 10.1073/pnas.1311073110. PubMed DOI PMC

Lacombat F.; Espagne A.; Dozova N.; Plaza P.; Müller P.; Brettel K.; Franz-Badur S.; Essen L.-O. Ultrafast Oxidation of a Tyrosine by Proton-Coupled Electron Transfer Promotes Light Activation of an Animal-like Cryptochrome. J. Am. Chem. Soc. 2019, 141, 13394–13409. 10.1021/jacs.9b03680. PubMed DOI

Gray H. B.; Winkler J. R. Hole hopping through tyrosine/tryptophan chains protects proteins from oxidative damage. Proc. Natl. Acad. Sci. U.S.A. 2015, 112, 10920–10925. 10.1073/pnas.1512704112. PubMed DOI PMC

Winkler J. R.; Gray H. B. Electron flow through biological molecules: does hole hopping protect proteins from oxidative damage?. QRB Discovery 2015, 48, 411–420. 10.1017/S0033583515000062. PubMed DOI PMC

Winkler J. R.; Gray H. B. Long-Range Electron Tunneling. J. Am. Chem. Soc. 2014, 136, 2930–2939. 10.1021/ja500215j. PubMed DOI PMC

Shih C.; Museth A. K.; Abrahamsson M.; Blanco-Rodriguez A. M.; Di Bilio A. J.; Sudhamsu J.; Crane B. R.; Ronayne K. L.; Towrie M.; Vlček A. Jr.; et al. Tryptophan-Accelerated Electron Flow Through Proteins. Science 2008, 320, 1760–1762. 10.1126/science.1158241. PubMed DOI

Záliš S.; Heyda J.; Šebesta F.; Winkler J. R.; Gray H. B.; Vlček A. Photoinduced hole hopping through tryptophans in proteins. Proc. Natl. Acad. Sci. U. S. A. 2021, 118, 5775–5785. 10.1073/pnas.2024627118. PubMed DOI PMC

Takematsu K.; Williamson H. R.; Nikolovski P.; Kaiser J. T.; Sheng Y.; Pospíšil P.; Towrie M.; Heyda J.; Hollas D.; Záliš S.; et al. Two Tryptophans are Better than One in Accelerating Electron Flow Through a Protein. ACS Cent. Sci. 2019, 5, 192–200. 10.1021/acscentsci.8b00882. PubMed DOI PMC

Koch W.; Holthausen M. C.. A Chemist’s Guide to Density Functional Theory. 2 ed.; Wiley-VCH Verlag GmbH: Weinheim, 2001.

Yu H. S.; Li S. L.; Truhlar D. G. Perspective: Kohn-Sham density functional theory descending a staircase. J. Chem. Phys. 2016, 145, 130901.10.1063/1.4963168. PubMed DOI

Ufimtsev I. S.; Martínez T. J. Quantum Chemistry on Graphical Processing Units. 3. Analytical Energy Gradients and First Principles Molecular Dynamics. J. Chem. Theor. Comp. 2009, 5, 2619–2628. 10.1021/ct9003004. PubMed DOI

Titov A. V.; Ufimtsev I. S.; Luehr N.; Martínez T. J. Generating Efficient Quantum Chemistry Codes for Novel Architectures. J. Chem. Theor. Comp. 2013, 9, 213–221. 10.1021/ct300321a. PubMed DOI

Case D. A.; Berryman J. T.; Betz R. M.; Cerutti D. S. III; Cheatham T. E. C.; Darden T. A.; Duke R. E.; Giese T. J.; Gohlke H.; Goetz A. W.; Homeyer N., et al.AMBER 2014; University of California: San Francisco, 2015.

Adamo C.; Scuseria G. E.; Barone V. Accurate excitation energies from time-dependent density functionl theory: Assessing the PBE0 model. J. Chem. Phys. 1999, 111, 2889–2899. 10.1063/1.479571. DOI

Adamo C.; Barone V. Toward reliable density functional methods without adjustable parameters: The PBE0 model. J. Chem. Phys. 1999, 110, 6158–6170. 10.1063/1.478522. DOI

Grimme S.; Antony J.; Ehrlich S.; Krieg H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 132, 154104.10.1063/1.3382344. PubMed DOI

Yanai T.; Tew D. P.; Handy N. C. A new hybrid exchange-correlation functional using the Coulomb-attenuating method (CAM-B3LYP). Chem. Phys. Lett. 2004, 393, 51–57. 10.1016/j.cplett.2004.06.011. DOI

Wu Q.; Van Voothis T. Constrained Density Functional Theory and Its Application in Long-Range Electron Transfer. J. Chem. Theory Comput. 2006, 2, 765–774. 10.1021/ct0503163. PubMed DOI

Mao Y.; Montoya-Castillo A.; Markland T. E. Excited state diabatization on the cheap using DFT: Photoinduced electron and hole transfer. J. Chem. Phys. 2020, 153, 244111.10.1063/5.0035593. PubMed DOI

Epifanovsky E.; Gilbert A. T. B.; Feng X.; Lee J.; Mao Y.; Mardirossian N.; Pokhilko P.; White A. F.; Coons M. P.; Dempwolff A. L.; et al. Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package. J. Chem. Phys. 2021, 155, 08480110.1063/5.0055522. PubMed DOI PMC

Marenich A. V.; Jerome S. V.; Cramer C. J.; Truhlar D. G. Charge Model 5: An Extension of Hirshfeld Population Analysis for the Accurate Description of Molecular Interactions in Gaseous and Condensed Phases. J. Chem. Theory Comput. 2012, 8, 527–541. 10.1021/ct200866d. PubMed DOI

Marazzi M.; Gattuso H.; Fumanal M.; Daniel C.; Monari A. Charge transfer vs. charge separated triplet excited states of [ReI(dmp)(CO)3(His124)(Trp122)]+ in water and in modified Pseudomonas aeruginosa azurin protein. Chem.—Eur. J. 2019, 25, 2519–2526. 10.1002/chem.201803685. PubMed DOI

Wu Q.; Cheng C.-L.; Van Voorhis T. Configuration interaction based on constrained density functional theory: A multireference method. J. Chem. Phys. 2007, 127, 164119.10.1063/1.2800022. PubMed DOI

Pospíšil P.; Sýkora J.; Takematsu K.; Hof M.; Gray H. B.; Vlček A. Light-Induced Nanosecond Relaxation Dynamics of Rhenium-Labeled Pseudomonas aeruginosa Azurins. J. Phys. Chem. B 2020, 124, 788–797. 10.1021/acs.jpcb.9b10802. PubMed DOI

Blanco-Rodríguez A. M.; Busby M.; Ronayne K. L.; Towrie M.; Grădinaru C.; Sudhamsu J.; Sýkora J.; Hof M.; Záliš S.; Di Bilio A. J.; et al. Relaxation Dynamics of [ReI(CO)3(phen)(HisX)]+ (X = 83, 107, 109, 124, 126) Pseudomonas aeruginosa Azurins. J. Am. Chem. Soc. 2009, 131, 11788–11800. 10.1021/ja902744s. PubMed DOI

Blumberger J. Recent Advances in the Theory and Molecular Simulation of Biological Electron Transfer Reactions. Chem. Rev. 2015, 115, 11191–11238. 10.1021/acs.chemrev.5b00298. PubMed DOI

Oberhofer H.; Reuter K.; Blumberger J. Charge Transport in Molecular Materials: An Assessment of Computational Methods. Chem. Rev. 2017, 117, 10319–10357. 10.1021/acs.chemrev.7b00086. PubMed DOI

Lin B.; Pettitt B. M. On the universality of proximal radial distribution functions of proteins. J. Chem. Phys. 2011, 134, 106101.10.1063/1.3565035. PubMed DOI PMC

Polák J.; Ondo D.; Heyda J. Thermodynamics of N-Isopropylacrylamide in Water: Insight from Experiments, Simulations, and Kirkwood–Buff Analysis Teamwork. J. Phys. Chem. B 2020, 124, 2495–2504. 10.1021/acs.jpcb.0c00413. PubMed DOI

Takematsu K.; Pospíšil P.; Pižl M.; Towrie M.; Heyda J.; Záliš S.; Kaiser J. T.; Winkler J. R.; Gray H. B.; Vlček A. Hole Hopping Across a Protein-Protein Interface. J. Phys. Chem. B 2019, 123, 1578–1591. 10.1021/acs.jpcb.8b11982. PubMed DOI PMC

Takematsu K.; Williamson H.; Blanco-Rodríguez A. M.; Sokolová L.; Nikolovski P.; Kaiser J. T.; Towrie M.; Clark I. P.; Vlček A. Jr.; Winkler J. R.; et al. Tryptophan-Accelerated Electron Flow Across a Protein-Protein Interface. J. Am. Chem. Soc. 2013, 135, 15515–15525. 10.1021/ja406830d. PubMed DOI PMC

Lu Y.; Kundu M.; Zhong D. Effects of nonequilibrium fluctuations on ultrafast short-range electron transfer dynamics. Nat. Commun. 2020, 11, 2822.10.1038/s41467-020-15535-y. PubMed DOI PMC

Krishnan S.; Aksimentiev A.; Lindsay S.; Matyushov D. Long-Range Conductivity in Proteins Mediated by Aromatic Residues. ACS Physical Chemistry Au 2023, 3, 444–455. 10.1021/acsphyschemau.3c00017. PubMed DOI PMC

Blumberger J. Electron transfer and transport through multi-heme proteins: recent progress and future directions. Curr. Opin. Chem. Biol. 2018, 47, 24–31. 10.1016/j.cbpa.2018.06.021. PubMed DOI

Lu Y.; Zhong D. Understanding Short-Range Electron-Transfer Dynamics in Proteins. J. Phys. Chem. Lett. 2019, 10, 346–351. 10.1021/acs.jpclett.8b03749. PubMed DOI PMC

Kundu M.; He T.-F.; Lu Y.; Wang L.; Zhong D. Short-Range Electron Transfer in Reduced Flavodoxin: Ultrafast Nonequilibrium Dynamics Coupled with Protein Fluctuations. J. Phys. Chem. Lett. 2018, 9, 2782–2790. 10.1021/acs.jpclett.8b00882. PubMed DOI PMC

Yang J.; Zhang Y.; Lu Y.; Wang L.; Lu F.; Zhong D. Ultrafast Dynamics of Nonequilibrium Short-Range Electron Transfer in Semiquinone Flavodoxin. J. Phys. Chem. Lett. 2022, 13, 3202–3208. 10.1021/acs.jpclett.2c00057. PubMed DOI

Zhuang B.; Liebl U.; Vos M. H. Flavoprotein Photochemistry: Fundamental Processes and Photocatalytic Perspectives. J. Phys. Chem. B 2022, 126, 3199–3207. 10.1021/acs.jpcb.2c00969. PubMed DOI

Woiczikowski P. B.; Steinbrecher T.; Kubař T.; Elstner M. Nonadiabatic QM/MM Simulations of Fast Charge Transfer in Escherichia coli DNA Photolyase. J. Phys. Chem. B 2011, 115, 9846–9863. 10.1021/jp204696t. PubMed DOI

Blanco-Rodríguez A. M.; Di Bilio A. J.; Shih C.; Museth A. K.; Clark I. P.; Towrie M.; Cannizzo A.; Sudhamsu J.; Crane B. R.; Sýkora J.; Winkler J. R.; Gray H. B.; Záliš S.; Vlček A. Jr. Phototriggering Electron Flow through ReI-modified Pseudomonas aeruginosa Azurins. Chem.—Eur. J. 2011, 17, 5350–5361. 10.1002/chem.201002162. PubMed DOI PMC

Bogdanov A. M.; Acharya A.; Titelmayer A. V.; Mamontova A. V.; Bravaya K. B.; Kolomeisky A. B.; Lukyanov K. A.; Krylov A. I. Turning On and Off Photoinduced Electron Transfer in Fluorescent Proteins by π-Stacking, Halide Binding, and Tyr145 Mutations. J. Am. Chem. Soc. 2016, 138, 4807–4817. 10.1021/jacs.6b00092. PubMed DOI

Liu Z.; Tan C.; Guo X.; Li J.; Wang L.; Zhong D. Dynamic Determination of Active-Site Reactivity in Semiquinone Photolyase by the Cofactor Photoreduction. J. Phys. Chem. Lett. 2014, 5, 820–825. 10.1021/jz500077s. PubMed DOI PMC

Lacombat F.; Espagne A.; Dozova N.; Plaza P.; Ignatz E.; Kiontke S.; Essen L.-O. Delocalized hole transport coupled to sub-ns tryptophanyl deprotonation promotes photoreduction of class II photolyases. Phys. Chem. Chem. Phys. 2018, 20, 25446.10.1039/C8CP04548H. PubMed DOI

Müller P.; Yamamoto J.; Martin R.; Iwai S.; Brettel K. Discovery and functional analysis of a 4th electron-transferring tryptophan conserved exclusively in animal cryptochromes and (6–4) photolyases. Chem. Commun. 2015, 51, 15502–15505. 10.1039/C5CC06276D. PubMed DOI

Immeln D.; Weigel A.; Kottke T.; Lustres J. L. P. Primary Events in the Blue Light Sensor Plant Cryptochrome:Intraprotein Electron and Proton Transfer Revealed by Femtosecond Spectroscopy. J. Am. Chem. Soc. 2012, 134, 12536–12546. 10.1021/ja302121z. PubMed DOI

Zhang M.; Wang L.; Zhong D. Photolyase: Dynamics and Mechanisms of Repair of Sun-Induced DNA Damage. Photochem. Photobiol. 2017, 93, 78–92. 10.1111/php.12695. PubMed DOI PMC

Lüdemann G.; Woiczikowski P. B.; Kubař T.; Elstner M.; Steinbrecher T. B. Charge Transfer in E. coli DNA Photolyase: Understanding Polarization and Stabilization Effects via QM/MM Simulations. J. Phys. Chem. B 2013, 117, 10769–10778. 10.1021/jp406319b. PubMed DOI

Lüdemann G.; Solov’yov I. A.; Kubař T.; Elstner M. Solvent Driving Force Ensures Fast Formation of a Persistent and Well-Separated Radical Pair in Plant Cryptochrome. J. Am. Chem. Soc. 2015, 137, 1147–1156. 10.1021/ja510550g. PubMed DOI

Cailliez F.; Müller P.; Firmino T.; Pernot P.; de la Lande A. Energetics of Photoinduced Charge Migration within the Tryptophan Tetrad of an Animal (6–4) Photolyase. J. Am. Chem. Soc. 2016, 138, 1904–1915. 10.1021/jacs.5b10938. PubMed DOI

Mendive-Tapia D.; Mangaud E.; Firmino T.; de la Lande A.; Desouter-Lecomte M.; Meyer H.-D.; Gatti F. Multidimensional Quantum Mechanical Modeling of Electron Transfer and Electronic Coherence in Plant Cryptochromes: The Role of Initial Bath Conditions. J. Phys. Chem. B 2018, 122, 126–136. 10.1021/acs.jpcb.7b10412. PubMed DOI

Ouyang Y.; Turek-Herman J.; Qiao T.; Hyster T. K. Asymmetric Carbohydroxylation of Alkenes Using Photoenzymatic Catalysis. J. Am. Chem. Soc. 2023, 145, 17018–17022. 10.1021/jacs.3c06618. PubMed DOI PMC

Li X.; Page C. G.; Zanetti-Polzi L.; Kalra A. P.; Oblinsky D. G.; Daidone I.; Hyster T. K.; Scholes G. D. Mechanism and Dynamics of Photodecarboxylation Catalyzed by Lactate Monooxygenase. J. Am. Chem. Soc. 2023, 145, 13232–13240. 10.1021/jacs.3c02446. PubMed DOI

Polizzi N. F.; Migliore A.; Therien M. J.; Beratan D. N. Defusing redox bombs?. Proc. Natl. Acad. Sci. U.S.A. 2015, 112, 10821–10822. 10.1073/pnas.1513520112. PubMed DOI PMC