Conformation-Induced Conductivity Switching in Bacterial Protein Nanowires*

Large-scale conformational changes in molecules are attractive because they can serve as information carriers for switches in memory and logic devices. Here we report the ability to control molecular conductivity via conformational switching at an unprecedented scale. Atomic force microscopy showed that individual Geobacter sulfurreducens protein nanowires undergo > 20 Å conformational change that propagates over their micrometer-lengths upon changing the environment. This increases the mechanical stiffness of nanowires by 4-fold and dc conductivity by 15,000-fold. Infrared nanospectroscopy revealed that this conformational change is driven by an internal structural transition. A suite of complementary experimental and computational methods such as X-ray diffraction, Raman, UV-Vis, fluorescence emission spectroscopy and circular dichroism further demonstrated this structural transition. Our studies thus establish nanoscopic approaches to visualize and quantify large-scale conformational changes in biomolecules and present novel strategies for tuning their structure and conductivity. Our work will guide the creation of a new class of programmable biomaterials with precisely controlled electronic and mechanical properties.