Abstract
Several species of δ proteobacteria are capable of reducing insoluble metal oxides as well as other extracellular electron acceptors. These bacteria play a critical role in the cycling of minerals in subsurface environments, sediments, and groundwater. In some species of bacteria such as Geobacter sulfurreducens, the transport of electrons is proposed to be facilitated by filamentous fibers that are referred to as bacterial nanowires. These nanowires are polymeric assemblies of proteins belonging to the type IVa family of pilin proteins and are mainly comprised of one subunit protein, PilA. Here, we report the high resolution solution NMR structure of the PilA protein from G. sulfurreducens determined in detergent micelles. The protein is >85% α-helical and exhibits similar architecture to the N-terminal regions of other non-conductive type IVa pilins. The detergent micelle interacts with the first 21 amino acids of the protein, indicating that this region likely associates with the bacterial inner membrane prior to fiber formation. A model of the G. sulfurreducens pilus fiber is proposed based on docking of this structure into the fiber model of the type IVa pilin from Neisseria gonorrhoeae. This model provides insight into the organization of aromatic amino acids that are important for electrical conduction.
Highlights
PilA is the major type IVa pilin that forms the conductive nanowires of Geobacter sulfurreducens
These clusters arise from the helical packing of the individual subunits, which results in close contact between
Framework for docking of other proteins, such as c-type cytochromes, that may be involved in EET by these nanowires
Summary
PilA is the major type IVa pilin that forms the conductive nanowires of Geobacter sulfurreducens. In some species of bacteria such as Geobacter sulfurreducens, the transport of electrons is proposed to be facilitated by filamentous fibers that are referred to as bacterial nanowires These nanowires are polymeric assemblies of proteins belonging to the type IVa family of pilin proteins and are mainly comprised of one subunit protein, PilA. Geobacter species represent important and abundant microorganisms that are capable of EET They putatively employ conductive nanowires to transfer electrons over comparatively long distances to extracellular electron acceptors [8]. We report the heterologous expression and structure determination of G. sulfurreducens PilA (GSu PilA) To our knowledge, this solution NMR structure is the first atomic resolution structure of a type IVa pilin that is involved in the formation of conductive bacterial nanowires. The structure was determined in the presence of 1,2-dihexanoyl-sn-glycero-3phosphocholine (DHPC) detergent micelles, revealing the interactions of a full-length type IVa pilin with a lipid environment
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