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    Investigating bacterial adhesion proteins as tools for controlling bacteria-surface interactions

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    Zahiri, Hossein
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    Abstract
    Adhesins are cell-surface proteins that initiate target binding and surface colonization by bacteria on the

    path to infection and biofilm formation. A deeper understanding of the interactions between adhesins and

    their ligands may lead to the development of strategies for controlling infection and biofilm formation.

    Using two ligand-binding domains from a model Repeats-in-toxin (RTX) adhesin in the Gram-negative

    marine bacterium Marinomonas primoryensis, I was able to prevent their binding to a photosynthetic

    diatom with which the bacteria form symbiotic biofilms underneath sea ice. The sugar-binding domain

    was optimally blocked with the monosaccharide fucose, and the peptide-binding domain was efficiently

    blocked with a peptide that ended in -Tyr-Thr-Asp. Homologs of these two ligand-binding domains are

    widespread in Gram-negative bacteria, including many pathogens. The same approach was employed to

    block the highly similar peptide-binding domain of FrhA adhesin of the pathogenic bacterium Vibrio

    cholerae from binding to the diatoms.

    Two adhesin engineering systems were explored as ways of altering the targeting of bacterial

    colonization. In one, redesigned and shortened versions of the M. primoryensis ice- and diatom-binding

    adhesin were tested for expression in Escherichia coli. In particular, the number of extender domains was

    reduced from 120 in the wild type to 15 or fewer. Although there was no evidence of ice-binding domain

    expression, antibodies to the extender domain and the diatom-binding domains detected these proteins on

    the outside of intact cells. A set of novel adhesins based on the beta-intimin system were designed using

    protein engineering techniques. In this series, a bacterial cellulose-binding module, and the peptide-binding domain of the M. primoryensis ice- and diatom-binding adhesin were separately fused to the end

    of the beta-intimin adhesin. In neither case was there any sign of external presentation of the binding

    domain. I suggest that these domains might have folded prior to passage through the adhesin pore, thus

    blocking export.
    URI for this record
    http://hdl.handle.net/1974/28571
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