Bottom-Up Fabrication of Protein Nanowires via Controlled Self-Assembly of Recombinant Geobacter Pilins

Metal-reducing bacteria in the genus Geobacter use a complex protein apparatus to guide the self-assembly of a divergent type IVa pilin peptide and synthesize conductive pilus appendages that show promise for the sustainable manufacturing of protein nanowires. The preferential helical conformation of the Geobacter pilin, its high hydrophobicity, and precise distribution of charged and aromatic amino acids are critical for biological self-assembly and conductivity. We applied this knowledge to synthesize via recombinant methods truncated pilin peptides for the bottom-up fabrication of protein nanowires and identified rate-limiting steps of pilin nucleation and fiber elongation that control assembly efficiency and nanowire length, respectively. The synthetic fibers retained the biochemical and electronic properties of the native pili even under chemical fixation, a critical consideration for integration of the nanowires into electronic devices. The implications of these results for the design and mass production of customized protein nanowires for diverse applications are discussed.