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

Metal-reducing bacteria in the genus 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 pili...

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Bibliographic Details
Published in:mBio 2019-12, Vol.10 (6)
Main Authors: Cosert, K M, Castro-Forero, Angelines, Steidl, Rebecca J, Worden, Robert M, Reguera, G
Format: Article
Language:English
Subjects:
Amino Acids, Aromatic - metabolism
Applied and Environmental Science
Editor's Pick
Electric Conductivity
Electron Transport - physiology
Fimbriae Proteins - metabolism
Fimbriae, Bacterial - metabolism
Geobacter - metabolism
Nanowires
Peptides - metabolism
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Summary:Metal-reducing bacteria in the genus 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 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. The discovery in 2005 of conductive protein appendages (pili) in the metal-reducing bacterium challenged our understanding of biological electron transfer and pioneered studies in electromicrobiology that revealed the electronic basis of many microbial metabolisms and interactions. The protein nature of the pili afforded opportunities for engineering novel conductive peptides for the synthesis of nanowires via cost-effective and scalable manufacturing approaches. However, methods did not exist for efficient production, purification, and assembly of pilins into nanowires. Here we describe platforms for high-yield recombinant synthesis of pilin derivatives and their assembly as protein nanowires with biochemical and electronic properties rivaling those of the native pili. The bottom-up fabrication of protein nanowires exclusively from pilin building blocks confirms unequivocally the charge transport capacity of the peptide assembly and establishes the intellectual foundation needed to manufacture pilin-based nanowires in bioelectronics and other applications.
ISSN:2161-2129
2150-7511
DOI:10.1128/mBio.02721-19