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      • HARVEST
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      Identification of protein-protein interactions in the type two secretion system of aeromonas hydrophila

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      Date
      2009
      Author
      Zhong, Su
      Type
      Thesis
      Degree Level
      Masters
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      Abstract
      The type II secretion system is used by many pathogenic and non-pathogenic bacteria for the extracellular secretion of enzymes and toxins. Aeromonas hydrophila is a Gram-negative pathogen that secretes proteins via the type II secretion system. In the studies described here, a series of yeast two-hybrid assays was performed to identify protein-protein interactions in the type II secretion system of A. hydrophila. The periplasmic domains of ExeA and ExeB were assayed for interactions with the periplasmic domains of Exe A, B, C, D, K, L, M, and N. Interactions were observed for both ExeA and ExeB with the secretin ExeD in one orientation. In addition, a previously identified interaction between ExeC and ExeD was observed. In order to further examine and map these interactions, a series of eight two-codon insertion mutations in the amino terminal domain of ExeD was screened against the periplasmic domains of ExeA and ExeB. As a result, the interactions were verified and mapped to subdomains of the ExeD periplasmic domain. To positively identify the region of ExeD involved in the interactions with ExeA, B, C and D, deletion mutants of ExeD were constructed based on the two-codon insertion mutation mapping of subdomains of the ExeD periplasmic domain, and yeast two-hybrid assays were carried out. The results showed that a fragment of the periplasmic domain of ExeD, from amino acid residue 26 to 200 of ExeD, was involved in the interactions with ExeA, B and C. As an independent assay for interactions between ExeAB and the secretin, His-tagged derivatives of the periplasmic domains of ExeA and ExeB were constructed and co-purification on Ni-NTA agarose columns was used to test for interactions with untagged ExeD. These experiments confirmed the interaction between ExeA and ExeD, although there was background in the co-purification test. These results provide support for the hypothesis that the ExeAB complex functions to organize the assembly of the secretin through interactions between both peptidoglycan and the secretin that result in its multimerization into the peptidoglycan and outer membrane layers of the envelope.
      Degree
      Master of Science (M.Sc.)
      Department
      Microbiology and Immunology
      Program
      Microbiology and Immunology
      Supervisor
      Howard, S. Peter
      Committee
      Napper, Scott; Goldie, Hughes; Xiao, Wei
      Copyright Date
      2009
      URI
      http://hdl.handle.net/10388/etd-03062009-132218
      Subject
      protein-protein interaction
      type two secretion system
      Aeromonas hydrophila
      yeast two-hybrid assay
      co-purification
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