Author ORCID Identifier
Date of Award
Doctor of Philosophy (PhD)
Iron is an essential nutrient for many pathogenic bacteria, and the most abundant source of the metal in the host is heme. Heme is often degraded by a heme oxygenase, and the first such enzyme (HO-1) was discovered in mammals. Many bacteria have homologous enzymes that allow them to leverage on the host heme pool during infection. Still, other bacteria that can degrade heme do not code for HO-1 like proteins. In Chapter 1, I conducted a comprehensive review of heme degrading enzymes in bacteria, describing four distinct families and focusing on structural and functional properties. In Chapter 2, I described the biochemical and genetic characterization of HupZ, a putative heme degrading protein from Group A Streptococcus (GAS, or Streptococcus pyogenes). I demonstrated that HupZ binds heme b without an axial ligand; therefore, the iron is not coordinated. HupZ also accommodates heme c, in which an external histidine residue coordinates the iron. In vitro studies showed that in the presence of a reducing partner, HupZ breakdowns heme c and heme b, but it requires an exogenous imidazole group to coordinate the iron. A knockout hupZ mutant exhibited reduced growth on heme iron and increased sensitivity to heme. Additionally, the expression of HupZ in Lactococcus lactis allowed for increased utilization of hemoglobin as the sole iron source. Together, the data demonstrate that HupZ is a unique heme binding and degrading protein that promotes heme metabolism and tolerance in GAS. In Chapter 3, I used structural modeling and prediction to examine the function of two heme-binding proteins from GAS. I used comparative modeling to map the binding region of an inhibitory monoclonal antibody to the heme capturing protein, Shr, and iterative threading to predict the structure of SiaF, a novel energy coupling factor transporter that imports heme. Altogether my work advances the understanding of heme binding and degradation in GAS and related bacterial pathogens.
Lyles, Kristin V., "Protein interactions with heme are vital for pathogenic bacteria, particularly in the utilization of heme as an iron source." Dissertation, Georgia State University, 2021.
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