Date of Award
2026
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Dali Liu
Abstract
Pyridoxal 5’-phosphate (PLP) is a highly versatile cofactor for many proteins and enzymes in the field of biochemistry. The cofactor’s multifaceted function is evident through stabilization of several reaction intermediates upon engaging a molecular effector or substrate. Currently, areas of biotechnology and drug design exploit the reactivity of PLP-dependent proteins and enzymes for therapeutic purposes. In recent decades, the PLP-dependent enzyme ornithine aminotransferase (OAT) has been identified as a potential target for inactivation in the treatment of hepatocellular carcinoma (HCC) due to its demonstrated overexpression in malignant tumor cells. Various studies have utilized cyclic GABA analogs to bind and inactivate OAT through irreversible covalent linkage to PLP, exploiting the promiscuity of PLP-dependent enzymes and versatile function of the PLP cofactor. To continue optimization of inactivator design, inactivation mechanisms must be thoroughly investigated. A PLP-dependent transcriptional regulator protein, GabR, binds to a primary inhibitory neurotransmitter, gamma (γ)-aminobutyric acid (GABA), as its molecular effector through formation of a reversible external aldimine between GABA and PLP. This interaction induces a specific conformational change in GabR and is accompanied by a shift in the protein’s intrinsic fluorescence intensity, providing a desirable framework for designing a biosensor capable of fluorescent signal generation in response to changes in GABA concentrations. The ability to quantify GABA in techniques such as neurological imaging and assays is crucial in gaining a global perspective on its role in various neurological diseases and disorders. In this dissertation, the mechanisms of inactivation of OAT for the treatment of hepatocellular carcinoma will be elucidated through X- ray crystallography, UV-vis spectrophotometry, and fluorine nuclear magnetic resonance spectroscopy (19F NMR). Additionally, a biosensor for GABA will be designed and evaluated using a combination of X-ray crystallography, UV-vis spectrophotometry, and fluorescence spectroscopy.
Recommended Citation
Vargas, Abigail Lynn, "From Mechanism-based Inactivation to Biosensor Development: Functional Versatility of Pyridoxal 5′-phosphate-dependent Enzymes and Proteins for Therapeutic Applications" (2026). Dissertations. 4316.
https://ecommons.luc.edu/luc_diss/4316
