Biomimetic Peptide Nanowires Designed for Conductivity

Abstract

The filamentous peptide-based nanowires produced by some dissimilatory metal-reducing bacteria, such as Geobacter sulfurreducens, display excellent natural conductivity. Their mechanism of conduction is assumed to be a combination of delocalized electrons through closely aligned aromatic amino acids and hopping/charge transfer. The proteins that form these microbial nanowires are structured from a coiled-coil, for which the design rules have been reported in the literature. Furthermore, at least one biomimetic system using related synthetic peptides has shown that the incorporation of aromatic residues can be used to enhance conductivity of peptide fibers. Herein, the de novo design of peptide sequences is used to enhance the conductivity of peptide gels, as inspired by microbial nanowires. A critical factor hampering investigations in both microbiology and materials development is inconsistent reporting of biomaterial conductivity measurements, with consistent methodologies needed for such investigations. We have reported a method herein to analyze non-Ohmic behavior using existing parameters, which is a statistically insightful approach for detecting small changes in biologically based samples. Aromatic residues were found to contribute to peptide gel conductivity, with the importance of the peptide confirmation and fibril assembly demonstrated both experimentally and computationally. This is a small step (in combination with parallel research under way by other researchers) toward developing effective peptide-based conducting nanowires, opening the door to the use of electronics in water and physiological environments for bioelectronic and bioenergy applications.

Challenges in engineering conductive protein fibres: Disentangling the knowledge

“…[18,[36][37][38][39][40] Dissimilar experimental conditions such as the state of the material and surrounding environment have been highlighted as possible culprits. [29,30,41,42] The recent expansion of the field into the engineering of novel conductive protein materials has been based on design principles directly inspired by G. sulfurreducens, [19][20][21][22] making it all the more critical that G. sulfurreducens' electronic behaviour is well-understood. Without understanding how experimental conditions impact measurements, the rational design, accurate comparison, and evaluation of novel conductive protein materials become infinitely more difficult.…”

“…With varied pH or buffer concentrations, a shift in the location of the fluorescence peaks and a change in their intensity were observed for this peptide. [20] The peptide was titrated with sodium bicarbonate, causing an increase in pH with time, and resulting in a decrease in peak intensity. This evidence suggests that the conformation of the peptide was dependent on pH, which had an effect on the formation of peptide fibrils and on their conductivity.…”

“…Therefore, measuring conductivity of proteins and peptides at different pH values can lead to varying results depending on the effects of ions and pH on conduction pathways. [20] Proteins are used in biological sensors that convert a change in a physiological input into an electric signal. pH can interfere in the sensor's readings, as it affects protein conduction pathways.…”

“…The current-voltage responses of various engineered proteins have been just as diverse. Synthetic alpha helical peptides displayed both power law behaviour (Figure 5A), [20] and linear current-voltage responses (Figure 5B). [22] Modified curli fibre proteins from E. coli with an attached aromatic rich peptide sequence displayed linear responses ( Figure 5C), [21] while aromatic substitutions on the protein itself displayed a transition from linear to power law depending on the voltage applied ( Figure 5D).…”

“…In fact, various types of synthetic conductive protein fibres have recently been engineered using recombinant DNA technologies and engineered microbes as chassis. [19][20][21][22] These novel conductive biomaterials hold Sophia Roy and Oliver Xie contributed equally.…”