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Hole Hopping Across a Protein–Protein Interface

Takematsu, Kana and Pospíšil, Petr and Pižl, Martin and Towrie, Michael and Heyda, Jan and Záliš, Stanislav and Kaiser, Jens T. and Winkler, Jay R. and Gray, Harry B. and Vlček, Antonín (2019) Hole Hopping Across a Protein–Protein Interface. Journal of Physical Chemistry B, 123 (7). pp. 1578-1591. ISSN 1520-6106. PMCID PMC6384139.

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We have investigated photoinduced hole hopping in a Pseudomonas aeruginosa azurin mutant Re126WWCuI, where two adjacent tryptophan residues (W124 and W122) are inserted between the Cu^I center and a Re photosensitizer coordinated to a H126 imidazole (Re = Re^I(H126)(CO)_3(dmp)^+, dmp = 4,7-dimethyl-1,10-phenanthroline). Optical excitation of this mutant in aqueous media (≤40 μM) triggers 70 ns electron transport over 23 Å, yielding a long-lived (120 μs) Re^I(H126)(CO)_3(dmp&•–)WWCu^(II) product. The Re126FWCu^I mutant (F124, W122) is not redox-active under these conditions. Upon increasing the concentration to 0.2–2 mM, {Re126WWCu^I}_2 and {Re126FWCu^I}_2 are formed with the dmp ligand of the Re photooxidant of one molecule in close contact (3.8 Å) with the W122′ indole on the neighboring chain. In addition, {Re126WWCu^I}_2 contains an interfacial tryptophan quadruplex of four indoles (3.3–3.7 Å apart). In both mutants, dimerization opens an intermolecular W122′ → //*Re ET channel (// denotes the protein interface, *Re is the optically excited sensitizer). Excited-state relaxation and ET occur together in two steps (time constants of ∼600 ps and ∼8 ns) that lead to a charge-separated state containing a Re(H126)(CO)3(dmp•–)//(W122^•+)′ unit; then (Cu^I)′ is oxidized intramolecularly (60–90 ns) by (W122^•+)′, forming Re^I(H126)(CO)_3(dmp^•–)WWCu^I//(Cu^(II))′. The photocycle is closed by ∼1.6 μs Re^I(H126)(CO)_3(dmp^•–) → //(Cu^(II))′ back ET that occurs over 12 Å, in contrast to the 23 Å, 120 μs step in Re126WWCu^I. Importantly, dimerization makes Re126FWCu^I photoreactive and, as in the case of {Re126WWCu^I}_2, channels the photoproduced “hole” to the molecule that was not initially photoexcited, thereby shortening the lifetime of Re^I(H126)(CO)_3(dmp^•–)//Cu^(II). Although two adjacent W124 and W122 indoles dramatically enhance Cu^I → *Re intramolecular multistep ET, the tryptophan quadruplex in {Re126WWCu^I}_2 does not accelerate intermolecular electron transport; instead, it acts as a hole storage and crossover unit between inter- and intramolecular ET pathways. Irradiation of {Re126WWCu^(II)}_2 or {Re126FWCu^(II)}_2 also triggers intermolecular W122′ → //*Re ET, and the Re(H126)(CO)_3(dmp^•–)//(W122^•+)′ charge-separated state decays to the ground state by ∼50 ns Re^I(H126)(CO)_3(dmp^•–)^+ → //(W122^•+)′ intermolecular charge recombination. Our findings shed light on the factors that control interfacial hole/electron hopping in protein complexes and on the role of aromatic amino acids in accelerating long-range electron transport.

Item Type:Article
Related URLs:
URLURL TypeDescription Information CentralArticle
Takematsu, Kana0000-0002-2334-336X
Heyda, Jan0000-0002-9428-9508
Kaiser, Jens T.0000-0002-5948-5212
Winkler, Jay R.0000-0002-4453-9716
Gray, Harry B.0000-0002-7937-7876
Vlček, Antonín0000-0002-6413-8311
Additional Information:© 2019 American Chemical Society. Received: December 13, 2018; Revised: January 15, 2019; Published: January 23, 2019. This work was supported by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health under Award No. R01DK019038. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Further support was provided the Czech Science Foundation (GAČR) Grant No. 17-011375, the Czech Ministry of Education (MŠMT) Grant No. LTAUSA18026, “IT4Innovations National Supercomputing Center – LM2015070”, EPSRC Grant No. (UK) EP/R029687/1, the STFC Rutherford Appleton Laboratory (UK), and the Arnold and Mabel Beckman Foundation. We thank Dr. Hana Kvapilová (JH Institute) for the help with measuring TRIR spectra. Yuling Shen (Caltech) is acknowledged for the help with protein preparation. The authors declare no competing financial interest.
Funding AgencyGrant Number
Grantová Agentura České Republiky17-011375
Ministerstvo Školství, Mládeže a TělovýchovyLTAUSA18026
Engineering and Physical Sciences Research Council (EPSRC)EP/R029687/1
Arnold and Mabel Beckman FoundationUNSPECIFIED
Issue or Number:7
PubMed Central ID:PMC6384139
Record Number:CaltechAUTHORS:20190211-081130545
Persistent URL:
Official Citation:Hole Hopping Across a Protein–Protein Interface. Kana Takematsu, Petr Pospíšil, Martin Pižl, Michael Towrie, Jan Heyda, Stanislav Záliš, Jens T. Kaiser, Jay R. Winkler, Harry B. Gray, and Antonín Vlček. The Journal of Physical Chemistry B 2019 123 (7), 1578-1591 DOI: 10.1021/acs.jpcb.8b11982
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92816
Deposited By: Tony Diaz
Deposited On:12 Feb 2019 22:41
Last Modified:07 Apr 2020 15:07

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