title: Type-III secretion filaments as scaffolds for inorganic nanostructures.
abstract: Nanostructured materials exhibit unique magnetic, electrical and catalytic properties. These characteristics are determined by the chemical composition, size and shape of the nanostructured components, which are challenging to modulate on such small size scales and to interface with living cells. To address this problem, we are using a self-assembling filament protein, PrgI, as a scaffold for bottom-up inorganic nanostructure synthesis. PrgI is a small protein (80 amino acids) that oligomerizes to form the type-III secretion system needle of Salmonella enterica. We demonstrate that purified PrgI monomers also spontaneously self-assemble into long filaments and that high-affinity peptide tags specific for attachment to functionalized particles can be integrated into the N-terminal region of PrgI. The resulting filaments selectively bind to gold, whether the filaments are assembled in vitro, sheared from cells or remain attached to live S. enterica cell membranes. Chemical reduction of the gold-modified PrgI variants results in structures that are several micrometres in length and which incorporate a contiguous gold surface. Mutant strains with genomically incorporated metal-binding tags retain the secretion phenotype. We anticipate that self-assembled, cell-tethered protein/metal filamentous structures have applications in sensing and energy transduction in vivo.
authors.affiliation: Department of Bioengineering, University of California Berkeley, Berkeley, CA, USA.
authors.forename: Anum
authors.initials: A
authors.lastname: Azam
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of California Berkeley, Berkeley, CA, USA dtercek@berkeley.edu.
authors.forename: Danielle
authors.initials: D
authors.lastname: Tullman-Ercek
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D058947:Bacterial Secretion Systems; D002462:Cell Membrane / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006046:Gold / Q000737:chemistry*; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D049329:Nanostructures / Q000737:chemistry*; D019779:Salmonella enterica / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D046912:Multiprotein Complexes; D006046:Gold
keywords: biomineralization; microbial electrocatalysis; nanostructures; self-assembly; type-III secretion