Author ORCID Identifier
https://orcid.org/0009-0009-4689-8358
Defense Date
2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Microbiology & Immunology
First Advisor
Richard Marconi
Abstract
Lyme disease (LD) is the most common arthropod-borne disease in North America and is caused by the spirochete, Borreliella burgdorferi. LD spirochetes are maintained in an enzootic cycle of Ixodes species ticks and a vertebrate reservoir. The secondary messenger molecule c-di-GMP plays a crucial role in adaptive responses during the enzootic cycle. PlzA is the sole c-di-GMP-binding protein identified to date that is encoded by all Borreliella burgdorferi isolates. PlzA has both c-di-GMP-dependent and c-di-GMP-independent functions and is required to complete the enzootic cycle. The full range of PlzA regulatory activities has yet to be fully defined. We determined the atomic structure of the PlzA protein in complex with dimeric c-di-GMP. The structure revealed N- and C-terminal domains that consist of small β-barrel domains (SBB) that we hypothesize mediate RNA chaperone activities, including RNA binding, RNA annealing, displacement, and unwinding. PlzA RNA chaperone activity was demonstrated and found to be regulated by c-di-GMP. C-di-GMP negatively impacted the RNA displacement and RNA-unwinding activities of PlzA. In contrast, its RNA-binding and RNA annealing activities were not affected by the presence or absence of c-di-GMP. Utilizing FRET, we demonstrated that RNA binding to PlzA induces structural rearrangements. The crystal structure also revealed surface-exposed Phe residues within the N-terminal and C-terminal domains of PlzA. We hypothesize that the Phe residues are involved in ligand binding, specifically RNA binding. RNA binding studies showed that the site-directed substitution mutagenesis of specific Phe residues to Ala in the N-terminal and the C-terminal reduced or abolished RNA binding, respectively, when combined with mutations that removed c-di-GMP binding. We also demonstrated that PlzA binds DNA, and that the amino acid residues involved in RNA binding are also involved in DNA binding. The data presented within provides significant insight into the functional activities and functional determinants of PlzA.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
12-12-2025