title: Engineering the Salmonella type III secretion system to export spider silk monomers.
abstract: The type III secretion system (T3SS) exports proteins from the cytoplasm, through both the inner and outer membranes, to the external environment. Here, a system is constructed to harness the T3SS encoded within Salmonella Pathogeneity Island 1 to export proteins of biotechnological interest. The system is composed of an operon containing the target protein fused to an N-terminal secretion tag and its cognate chaperone. Transcription is controlled by a genetic circuit that only turns on when the cell is actively secreting protein. The system is refined using a small human protein (DH domain) and demonstrated by exporting three silk monomers (ADF-1, -2, and -3), representative of different types of spider silk. Synthetic genes encoding silk monomers were designed to enhance genetic stability and codon usage, constructed by automated DNA synthesis, and cloned into the secretion control system. Secretion rates up to 1.8 mg l(-1) h(-1) are demonstrated with up to 14% of expressed protein secreted. This work introduces new parts to control protein secretion in Gram-negative bacteria, which will be broadly applicable to problems in biotechnology.
authors.affiliation: Chemistry and Chemical Biology Graduate Program, University of California--San Francisco, San Francisco, CA 94110, USA.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Widmaier
authors.forename: Danielle
authors.initials: D
authors.lastname: Tullman-Ercek
authors.forename: Ethan A
authors.initials: EA
authors.lastname: Mirsky
authors.forename: Rena
authors.initials: R
authors.lastname: Hill
authors.forename: Sridhar
authors.initials: S
authors.lastname: Govindarajan
authors.forename: Jeremy
authors.initials: J
authors.lastname: Minshull
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Voigt
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D005349:Fibroins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D015202:Protein Engineering / Q000379:methods; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D012475:Salmonella / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D016415:Sequence Alignment; D015398:Signal Transduction; D013112:Spiders / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; C440638:SPI-2 protein, Salmonella; C419942:Spi1 protein, Salmonella; D005349:Fibroins