Structure of Geobacter pili reveals secretory rather than nanowire behaviour

Yangqi Gu, Vishok Srikanth, Aldo I. Salazar-Morales, Ruchi Jain, J. Patrick O’Brien, Sophia M. Yi, Rajesh Kumar Soni, Fadel A. Samatey, Sibel Ebru Yalcin and Nikhil S. Malvankar ()
Additional contact information
Yangqi Gu: Microbial Sciences Institute Yale University
Vishok Srikanth: Microbial Sciences Institute Yale University
Aldo I. Salazar-Morales: Microbial Sciences Institute Yale University
Ruchi Jain: Microbial Sciences Institute Yale University
J. Patrick O’Brien: Microbial Sciences Institute Yale University
Sophia M. Yi: Microbial Sciences Institute Yale University
Rajesh Kumar Soni: Proteomics and Macromolecular Crystallography Shared Resource, Herbert Irving Comprehensive Cancer Center, Columbia University Irving Medical Center
Fadel A. Samatey: Microbial Sciences Institute Yale University
Sibel Ebru Yalcin: Microbial Sciences Institute Yale University
Nikhil S. Malvankar: Microbial Sciences Institute Yale University

Nature, 2021, vol. 597, issue 7876, 430-434

Abstract: Abstract Extracellular electron transfer by Geobacter species through surface appendages known as microbial nanowires1 is important in a range of globally important environmental phenomena2, as well as for applications in bio-remediation, bioenergy, biofuels and bioelectronics. Since 2005, these nanowires have been thought to be type 4 pili composed solely of the PilA-N protein1. However, previous structural analyses have demonstrated that, during extracellular electron transfer, cells do not produce pili but rather nanowires made up of the cytochromes OmcS2,3 and OmcZ4. Here we show that Geobacter sulfurreducens binds PilA-N to PilA-C to assemble heterodimeric pili, which remain periplasmic under nanowire-producing conditions that require extracellular electron transfer5. Cryo-electron microscopy revealed that C-terminal residues of PilA-N stabilize its copolymerization with PilA-C (to form PilA-N–C) through electrostatic and hydrophobic interactions that position PilA-C along the outer surface of the filament. PilA-N–C filaments lack π-stacking of aromatic side chains and show a conductivity that is 20,000-fold lower than that of OmcZ nanowires. In contrast with surface-displayed type 4 pili, PilA-N–C filaments show structure, function and localization akin to those of type 2 secretion pseudopili6. The secretion of OmcS and OmcZ nanowires is lost when pilA-N is deleted and restored when PilA-N–C filaments are reconstituted. The substitution of pilA-N with the type 4 pili of other microorganisms also causes a loss of secretion of OmcZ nanowires. As all major phyla of prokaryotes use systems similar to type 4 pili, this nanowire translocation machinery may have a widespread effect in identifying the evolution and prevalence of diverse electron-transferring microorganisms and in determining nanowire assembly architecture for designing synthetic protein nanowires.

Date: 2021
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DOI: 10.1038/s41586-021-03857-w

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