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Title page for ETD etd-03242017-091315

Type of Document Dissertation
Author Frick-Cheng, Arwen Elise
URN etd-03242017-091315
Title The Molecular and Structural Analysis of the cag Type IV Secretion System Core Complex
Degree PhD
Department Microbiology and Immunology
Advisory Committee
Advisor Name Title
Mark Denison Committee Chair
Borden Lacy Committee Member
Eric Skaar Committee Member
Melanie Ohi Committee Member
Timothy Cover Committee Member
  • T4SS
  • bacteriology
  • electron microscopy
Date of Defense 2017-03-17
Availability restricted
Bacterial type IV secretion systems (T4SSs) can function to export or import DNA, and can deliver effector proteins into a wide range of target cells. Relatively little is known about the structural organization of T4SSs that secrete effector proteins. In this thesis, I describe the isolation and analysis of a membrane-spanning core complex from the Helicobacter pylori cag T4SS, which has an important role in the pathogenesis of gastric cancer. This complex contains five H. pylori proteins, CagM, CagT, Cag3, CagX, and CagY, each of which is required for cag T4SS activity. CagX and CagY are orthologous to the VirB9 and VirB10 components of T4SSs in other bacterial species, and the other three Cag proteins are unique to H. pylori. Negative stain single-particle electron microscopy revealed complexes 41 nm in diameter, characterized by a 19-nm-diameter central ring linked to an outer ring by spoke-like linkers. Incomplete complexes formed by Δcag3 or ΔcagT mutants retained the 19-nm-diameter ring but lack an organized outer ring. Immunogold labeling studies confirmed that Cag3 is a peripheral component of the complex. The cag T4SS core complex has an overall diameter and structural organization that differ considerably from the corresponding features of conjugative T4SSs. These results highlight specialized features of the H. pylori cag T4SS that are optimized for function in the human gastric mucosal environment.
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