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Nanosecond Heme-to-Heme Electron Transfer Rates in a Multiheme Cytochrome Nanowire Reported by a Spectrally Unique His/Met Ligated Heme

Van Wonderen, Jessica and Adamczyk, Katrin and Wu, Xiaojing and Jiang, Xiuyun and Piper, Samuel and Hall, Christopher and Edwards, Marcus and Clarke, Tom and Zhang, Huijie and Jeuken, Lars and Sazanovich, Igor and Towrie, Michael and Blumberger, Jochen and Meech, Steve and Butt, Julea (2021) 'Nanosecond Heme-to-Heme Electron Transfer Rates in a Multiheme Cytochrome Nanowire Reported by a Spectrally Unique His/Met Ligated Heme.' Proceedings of the National Academy of Sciences of USA, 118 (39). ISSN 0027-8424

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Proteins achieve efficient energy storage and conversion through electron transfer along a series of redox cofactors. Multiheme cytochromes are notable examples. These proteins transfer electrons over distance scales of several nanometers to >10 μm and in so doing they couple cellular metabolism with extracellular redox partners including electrodes. Here we report pump-probe spectroscopy that provides a direct measure of the intrinsic rates of heme-heme electron transfer in this fascinating class of proteins. Our study took advantage of a spectrally unique His/Met ligated heme introduced at a defined site within the decaheme extracellular MtrC protein of Shewanella oneidensis. We observed rates of heme-to-heme electron transfer on the order of 109 s-1 (3.7-4.3 Å edge-to-edge distance), in good agreement with predictions based on density functional and molecular dynamics calculations. These rates are amongst the highest reported for ground state electron transfer in biology. Yet, some fall 2-3 orders of magnitude below the Moser-Dutton ruler because electron transfer at these short distances is through-space and therefore associated with a higher tunneling barrier than the through-protein tunneling scenario that is usual at longer distances. Moreover, we show that the His/Met ligated heme creates an electron sink that stabilizes the charge separated state on the 100 microsecond time scale. This feature could be exploited in future designs of multiheme cytochromes as components of versatile photosynthetic biohybrid assemblies.

Item Type: Article
Uncontrolled Keywords: electron transfer; Moser–Dutton ruler; pump-probe spectroscopy; Ru(II)tris(bipyridine); Shewanella
Divisions: Faculty of Science and Health > Life Sciences, School of
Depositing User: Elements
Date Deposited: 01 Sep 2021 15:00
Last Modified: 05 Oct 2021 11:24

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