The Incredible Secret Electronic Life of Proteins

Proteins are commonly believed to be insulators, consistent with their appearance and the results of simple measurements. This is in line with the expected behavior of a disordered, wide bandgap solid with strong vibronic coupling. Yet some soil bacteria transfer electrons via thin protein filaments with near-metallic conductivities. Are they a special case? Motivated by calculations that indicate that many proteins have evolved towards a quantum critical structure¹ we decided to measure the conductance of single molecules of proteins chosen precisely because they lack redox centers and lack any known electron transfer function. Unique to our approach is the use of specific chemical bonding between proteins and electrodes to minimize the effects of contact resistance.² We find that nS conductances over distances of many nm are common. The conductance is limited by contacts, with very long electronic decay lengths inside the protien.³ What biological pressure could drive evolution towards this unlikely state? We have studied a functioning DNA polymerase, finding large changes in its internal conductance as it undergoes functional changes in conformation. This suggests a possible role for delocalized states in function. It also points to a new method for DNA sequencing based on direct electrical measurement of enzyme function.⁴

1. Vattay, G. et al. J. Phys,: Conf. Ser. 2015, 626, 012023.
2. Zhang, B et al. Proc Natl Acad Sci U S A 2019, 116, 5886.
3. Zhang, B.; Lindsay, S., Nano letters 2019, 19, 4017.
4. Zhang, B.; et al. ACS Nano 2019, https://doi.org/10.1021/acsnano.9b06875.