Mechanism of metal-like conductivity in bacterial protein nanowires

Proteins are considered electronically insulators. However, nanofilaments produced by Geobacter sulfurreducens exhibit metal-like conductivity. To elucidate the mechanism of electron transport, we measured the electrical and optical conductivity of filaments from multiple mutant strains as a function of molecular length, temperature, frequency, pH and π-stacking. We demonstrate that intrinsic conductivity of individual filaments can be described by theoretical model for quasi-one-dimensional materials. To determine the molecular architecture responsible for conductivity, we are using a suite of complementary experimental and computational methods. Our studies show that filaments show π-stacking, that can cause intermolecular electron delocalization, conferring metallic conductivity to filaments. Furthermore, increasing π-stacking improves their crystallinity, yielding a longer mean free path for electrons, and stronger electronic coupling which yields 1000 times lower electron attenuation than other proteins. These studies will help development of genetically programmable biomolecular materials with tunable functionality through precise control of their electronic and protein structure.