Proteins: Biomolecular Wires? - Prof. Dr. David Cahen
Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel
Proteins are surprisingly good solid-state electronic conductors. This holds also for proteins without any known biological electron transfer function. How do they do it?
To answer this question we measure solid-state electron transport (ETp) across proteins that are “dry” (only tightly bound water, to retain the conformation, still present). We compare results for the electron transfer (ET) protein, Azurin (Az), the proton-pumping membrane protein Bacteriorhodopsin (bR), and for Bovine Serum Albumin (BSA). Clear differences between these proteins are seen. For bR and Az we can show that they preserve their structure in the solid state measurement configuration. The results are sensitive to protein modification, e.g., removing or disconnecting the retinal in bR and removing or replacing the Cu redox centre in Az.
Insight in the ETp mechanism comes from temperature-dependent studies. Az shows 20-360K temperatureindependent ETp, until its denaturation temperature, indicative of tunneling. Cu removal changes this to thermally activated ETp, indicative of hopping. Below 200K all proteins and their variants show temperature-independent ETp. bR’s high thermal activation energy makes this protein a better electronic conductor above room temperature than the ET protein Az!
Putting our data in perspective by comparing them to all known protein ETp data in the literature, we conclude that, in general, proteins behave more like molecular wires than as insulators.
Collaboration with M. Sheves, I. Pecht, Work of L. Sepunaru, N. Amdursky, W. Li, ,N. Friedman, I. Ron, Y. Jin; all from the Weizmann Inst.; Support from the Minerva foundation (Munich).