Author ORCID Identifier

Defense Date


Document Type


Degree Name

Doctor of Philosophy


Microbiology & Immunology

First Advisor

Jason Carlyon


Obligate intracellular pathogens must invade host cells to survive and pose a global health risk. As such, internalization is a critical life stage and represents an excellent therapeutic target. Oxidoreductase exploitation is a thematic invasion strategy among obligate intracellular pathogens. Delineating the mechanisms and proteins mediating this exploitation could identify novel therapeutic targets for many important pathogens. Anaplasma phagocytophilum infects neutrophils by an incompletely defined mechanism, resulting in the emerging potentially fatal disease, human granulocytic anaplasmosis. The bacterial adhesin, Asp14, contributes to invasion by virtue of its C-terminus engaging an unknown receptor. Yeast two-hybrid analysis identified protein disulfide isomerase (PDI) as a putative Asp14 binding partner. Co-immunoprecipitation confirmed this interaction and identified the Asp14 C-terminus as critical to it. PDI reductase activity inhibition impaired bacterial infection of, but not binding to, host cells. A. phagocytophilum failed to productively infect myeloid-specific PDI conditional knock-out mice. This is the first demonstration of microbial PDI exploitation in vivo. Infection of PDI inhibited cells was rescued when bacterial, but not host surfaces were reduced with the reducing agent tris(2-carboxyethyl)phosphine (TCEP). Furthermore, TCEP restored bacterial infectivity after Asp14 inhibition using an antibody that reduces infection. Mutational analyses identified Asp14 residues critical for binding PDI. These data demonstrate that Asp14 binds and brings PDI to disulfide bonds within A. phagocytophilum surface protein(s) that it reduces, enabling infection. Targeting the Asp14 C-terminus could benefit approaches to prevent/treat granulocytic anaplasmosis. A similar approach would identify proteins from other obligate intracellular pathogens that could prove to be protective targets.


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Available for download on Saturday, July 13, 2024


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