UCLA

My research is focused on elucidating the mechanisms by which pathogenic bacteria harvest heme from human hemoglobin during infection using a combination of structural, biophysical, kinetic, and computational approaches. The model organism for this research was Corynebacterium diphtheriae, the etiological agent of diphtheria in humans and a representative member of the Actinomycetota (formerly Actinobacteria) phylum. Actinomycetota are high G-C, gram-positive pathogens distinguished by their characteristic “mycomembrane,” a layer of extensive covalent modification built upon the outer peptidoglycan layer that imparts unique cell-wall architecture distinct from that of prototypical low G-C gram-positive bacteria (e.g., Bacillota). Importantly, heme acquisition in Actinomycetota remains poorly understood. A better mechanistic understanding of how pathogens of this class exploit human heme through hemoglobin is foundational to a thorough understanding of Actinomycetota micronutrient acquisition and could support the development of alternative antivirulence therapeutics designed to block heme transport into the cell or hijack such uptake pathways to deliver fused antibioticheme analog compounds. Toward this goal, I have performed extensive functional and structural characterization of the Corynebacterium diphtheriae heme-acquisition system. In Chapter 2, I discuss the mathematical treatment and modeling of bacterial growth kinetics to develop a plausible model of Corynebacterium diphtheriae heme acquisition. In Chapter 3, I investigate and characterize the heme acquisition protein machinery via X-ray crystallography, ITC, UV-vis spectroscopy, and mass spectrometry. In Chapter 4, I characterize the action of secreted hemophore CR domains as usable iron sources for the bacteria through the use of a novel fluorogenic hemoglobin reporter. Chapter 5, consisting of unpublished work, focuses on the terminal step of heme import by examining the structures and transfer mechanisms of HmuT, the ligand-binding component of the heme ABC transporter. These studies have greatly broadened our understanding of bacterial heme acquisition while providing substantial evidence for an affinity-driven, directional heme flow pathway paradigm in Corynebacterium species.