Keywords

nitric-oxide, metalloenzymes, cytochrome-p450s

Abstract

Nitric oxide (NO) is a small, gaseous molecule that is toxic to life at high doses but serves a crucial role in biological processes at lower concentrations, including: cell signaling, immune response, and more recently, as a synthon in the biosynthesis of natural products in bacteria. Metalloenzymes are incredibly versatile catalysts that enable chemistry that often, still has no comparable laboratory reaction.

TxtE, a cytochrome P450 (CYP), utilizes NO as a co-substrate along with dioxygen (O2) to catalyze the regioselective nitration of L-tryptophan (Trp) to produce 4-NO2-Trp. Work in this dissertation established that the TxtE ferric-superoxo intermediate is resistant to reduction, which facilitates its reaction with diffusible NO en route to an , as yet,-uncharacterized nitrating species. Furthermore, it is shown that an outer-sphere protein residue influences the nitration chemistry of TxtE. A Thr250Ala mutant version of TxtE characterized and found to lack all nitration ability despite maintaining cofactor incorporation and retaining competence for formation of the ferric-superoxo intermediate. Separately, experiments performed with wild-type TxtE demonstrate that analogs of Trp affect the lifetime of the ferric-superoxo intermediate and enable substrate hydroxylation.

Additionally, a non-heme, diiron enzyme from Mycobacterium kansasii (MkaHLP) was previously established to possess NO peroxidase activity. In this dissertation, a Tyr54Phe mutant form of MkaHLP was characterized and found to have greatly diminished NO peroxidase activity due to the removal of the characteristic tyrosine ligand to the diiron site. Implications of this change in activity are discussed in the relevant section.

Completion Date

2024

Semester

Summer

Committee Chair

Caranto, Jonathan

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Chemistry

Degree Program

Chemistry PhD

Format

application/pdf

Release Date

8-15-2027

Length of Campus-only Access

3 years

Access Status

Doctoral Dissertation (Campus-only Access)

Campus Location

Orlando (Main) Campus

Accessibility Status

Meets minimum standards for ETDs/HUTs

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Restricted to the UCF community until 8-15-2027; it will then be open access.

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