Probing Quantum Interference Effects during Electron Transfer in Bacterial Pili Proteins

A cornerstone of quantum physics is the interference of electron waves arising from the superposition principle. Metallic conductivity is an effect of interference of partial electron waves multiply scattered at the ion cores of the crystal lattice. Metallic conductivity has been considered impossible in proteins. However, previously we have shown that protein nanofilaments called pili of Geobacter sulfurreducens show metallic-like conductivity [1]. In preliminary studies, we have found that pili exhibit signatures of quantum interference phenomena of weak localization, one of the unique cases where superposition principle of quantum mechanics leads to observable consequences in the macroscopic systems. Applying magnetic field increased the conductivity of pili at physiological temperatures as expected from weak localization effect in the metallic regime. In contrast, the pili conductivity decreased at lower temperatures, where pili show semiconducting behavior, as expected for the wavefunction shrinkage effect.
[1] Malvankar et al. Nature Nanotechnology, 6, 573-579 (2011)