Defense Date

2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Microbiology & Immunology

First Advisor

Richard Marconi

Abstract

Lyme disease is an emerging infection that is caused by the Borrelia burgdorferi sensu lato complex. These bacteria exist in nature through an enzootic life cycle involving Ixodes ticks and various reservoir hosts. One way that this bacterium adapts to the different hosts in the enzootic cycle is through the expression of outer surface protein C (OspC). OspC is a surface exposed lipoprotein encoded on circular plasmid 26 that forms homodimers on the bacterial surface and has distinct conserved and variable portions of sequence. When ospC is deleted, the spirochetes are unable to cause mammalian infection although the mechanism of this is unknown. Additionally, OspC is thought to be involved in reservoir host specificity/association and in tissue dissemination. In order to better understand the functional domains of OspC, the different conserved and variable portions of this protein were investigated. Three conserved portions of OspC were investigated: (1) the conserved cysteine residue at position 130 (C130), (2) the last ten C-terminal amino acids (C10), and (3) ligand binding domain 1 (LBD1). The C130 residue was mutated and this substitution disrupted OspC oligomerization in vitro and in vivo. A B. burgdorferi strain lacking the C10 retained full infectivity and plasminogen binding. The mutation of a single residue within LBD1 rendered B. burgdorferi noninfectious, indicating the importance of this domain in infection establishment. The variable portion of OspC was investigated by: (1) altering the surface charge of ligand binding domain 2 (LBD2), (2) inserting different OspC types into a constant genetic background, and (3) creating OspC hybrids. Alteration of the surface charge of LBD2 by site directed mutagenesis resulted in a lack of persistence in mice. By inserting an OspC type known to be noninfectious in mice into an infectious strain, infectivity was abolished. Strains expressing OspC hybrids indicated that multiple domains of OspC are involved in species specificity. Together these analyses demonstrated that OspC is as important protein that plays multiple roles in pathogenesis. The work presented here helps to increase the understanding of this crucial protein and the strains described can be used to decipher the full function of OspC.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

August 2011

Available for download on Sunday, August 08, 2021

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