Illustration of the structure of a protein nanowire formed of cytochrome OmcE subunits from the bacterium Geobacter sulfurreducens. These filaments are electrically conductive extracellular appendages found on the surface of G. sulfurreducens. They enable long-distance electron transport to the environment or other microbial cells. Bacterial nanowires are being studied for use in bioelectrochemical devices and sustainable electronic materials.