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Publication Abstract from PubMed

Rapid and directed electron transfer (ET) is essential for biological processes. While the rates of ET over 1-2 nanometers in proteins can largely be described by simplified non-adiabatic theory, it is not known how these processes scale to microscopic distances. We generated crystalline lattices of Small Tetraheme Cytochromes (STC) forming well-defined, three-dimensional networks of closely-spaced redox centers that appear to be nearly ideal for multistep ET. Electrons were injected into specific locations in the STC crystals by direct photoreduction and their redistribution was monitored by imaging. The results demonstrate ET over mesoscopic to microscopic (~100 mum) distances through sequential hopping in a biologically-based heme network. We estimate that a hypothetical "nanowire" composed of crystalline STC with a cross-section about 100 cytochromes could support the anaerobic respiration of a Shewanella cell. The crystalline lattice insulates mobile electrons from oxidation by O2, compared to those in cytochromes in solution, potentially allowing for efficient delivery of current without production of reactive oxygen species. The platform allows direct tests of whether the assumptions based on short-range ET hold for sequential ET over mesoscopic distances. We estimate that the interprotein ET across 6 A between hemes in adjacent proteins was about 10(5) s(-1), about 100-fold slower than expectations based on simplified theory. More detailed analyses implied that additional factors, possibly contributed by the crystal lattice, may strongly impact mesoscale ET mainly by increasing the reorganizational energy of interprotein ET, suggesting design strategies for engineering improved nanowires suitable for future bioelectronic materials.

Mesoscopic to Macroscopic Electron Transfer by Hopping in a Crystal Network of Cytochromes.,Huang J, Zarzycki J, Gunner MR, Parson WW, Kern JF, Yano J, Ducat DC, Kramer DM J Am Chem Soc. 2020 May 14. doi: 10.1021/jacs.0c02729. PMID:32406683^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.