Shallow conductance decay along the heme array of a single tetraheme protein wire

Kavita Garg, Zdenek Futera, Xiaojing Wu, Yongchan Jeong, Rachel Chiu, Varun Chittari Pisharam, Tracy Ha, Albert Aragones, Jessica H. van Wonderen, Julea N. Butt, Jochen Blumberger, Ismael Diez-Perez

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Multiheme cytochromes (MHCs) are the building blocks of highly conductive micrometre-long supramolecular wires found in so-called electrical bacteria. Recent studies have revealed that these proteins possess a long supramolecular array of closely packed heme cofactors along the main molecular axis alternating between perpendicular and stacking configurations (TST = T-shaped, Stacked, T-shaped). While TST arrays have been identified as the likely electron conduit, the mechanisms of outstanding long-range charge transport observed in these structures remain unknown. Here we study charge transport on individual small tetraheme cytochromes (STCs) containing a single TST heme array. Individual STCs are trapped in a controllable nanoscale tunnelling gap. By modulating the tunnelling gap separation, we are able to selectively probe four different electron pathways involving 1, 2, 3 and 4 heme cofactors, respectively, leading to the determination of the electron tunnelling decay constant along the TST heme motif. Conductance calculations of selected single-STC junctions are in excellent agreement with experiments and suggest a mechanism of electron tunnelling with shallow length decay constant through an individual STC. These results demonstrate that an individual TST motif supporting electron tunnelling might contribute to a tunnelling-assisted charge transport diffusion mechanism in larger TST associations.
Original languageEnglish
JournalChemical Science
Early online date3 Jul 2024
Publication statusE-pub ahead of print - 3 Jul 2024

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