On the electron transfer through Geobacter sulfurreducens PilA protein

Abstract

Geobacter sulfurreducens pili composed of the Type IV pili structural peptide PilA have been implicated as efficient electronic conductors. Though investigated experimentally, no detailed theoretical studies have been performed to date that provide quantitative estimation of the transmission spectrum, electron transfer (ET) paths, efficiency of current generation, and other factors needed for understanding possible mechanisms of conductivity. In the present work, we calculate from first principles the possibilities of electron tunneling through 3 PilA fragments which structure was identified recently by NMR. The results indicate that positively charged amino acids, arginines and lysines form electrostatic traps in the middle of the peptide preventing ET at low bias voltages (<∼6 V). At higher biases the traps are filled with electrons making possible sequential electron tunneling through the central part of the protein. In addition, leucines and phenylalanines form ET loops facilitating electron stabilization within the protein and sequential ET. Our results indicate that ET through the PilA protein cannot occur by coherent ET, but suggest a sequential (incoherent) mechanism. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1706–1717

Conductivity of individual Geobacter pili

“…[6][7][8][9][10]12 Models that include a role of c-type cytochromes in electron conduction along the length of the pili, 7,9,10 must account for conductivity measured here in reaches of the pili that were cytochrome free. The major impact of proton-doping on conductivity should also be accommodated.…”

“…4,5 However, this concept has been challenged repeatedly on the basis of theoretical modelling or inferences from biolm behaviour. [6][7][8][9][10][11][12] Remarkably, amongst this controversy the most basic data requirement, an estimate of the conductivity of individual pili, has been missing. Therefore, a low-noise nano-electrode measurement platform was devised to directly measure the conductivity of individual pili ( Fig.…”

Microbial nanowires: an electrifying tale

“…However, it is debatable whether these aromatic amino acids transfer electrons by metallic conduction or by multistep hopping. Multiple modelling studies strongly support the hypothesis that electron transfer through Geobacter MNWs occurs by multistep hopping among aromatic amino acids (Feliciano et al, 2015;Lebedev et al, 2015;Yan et al, 2015). This hypothesis was further strengthened by a recent report where experimental evidence has been provided to support multistep hopping in Geobacter MNWs where cryogenic STM of Geobacter pili showed thermal activation of the differential transversal conductance at low voltages which is in accordance with the electron hopping mechanism .…”

A review on sediment microbial fuel cells as a new source of sustainable energy and heavy metal remediation: mechanisms and future prospective

“…Thus, OmcZ is very important for the electron transfer to electrodes and for the formation of biofilms. According to immunogold studies, biofilms of G. sulfurreducens grew well on the graphite with fumarate because of the high production of OmcZ . Furthermore, OmcF gene deletion reduced the current production because OmcF was not only involved in exoelectrogen mechanisms but also necessary for the transcription of many genes required for current production in SMFCs .…”