Heme is vital to a variety of cellular functions in bacteria ranging from energy generation to iron reserve. Group A streptococcus (GAS) is a prevalent bacterial pathogen that is responsible for an array of human diseases ranging from simple, self-limiting, mucosal and skin infections to invasive and systemic manifestations. GAS needs iron for growth and can satisfy this nutritional requirement by scavenging the metal from heme. The pathogen produces powerful hemolysins that facilitate heme release during infection. Heme is captured and relayed through the GAS cell wall and cytoplasmic membrane by dedicated receptors and transporters. To-date, the fate of the acquired heme is unknown in Streptococci. Although heme is nutritionally beneficial for GAS growth, its pro-oxidant and lipophilic nature makes it a liability with damaging effects on cellular components. The conundrum associated with heme use is particularly pertinent to GAS pathophysiology since invasive GAS infections involve massive hemolysis and the generation of unescorted heme in excess. In this dissertation, I aimed to describe the mechanisms that GAS uses for heme catabolism while managing its toxicity. I conducted a biochemical characterization of a new enzyme, HupZ in GAS that degrades heme in vitro. Similar to the heme oxygenase-1 (HO-1), HupZ activity leads to the formation of iron, CO, and a biliverdin-like product. I also investigated the impact of heme on GAS physiology and identified key mediators in the repair and detoxification process. This study demonstrated that heme exposure leads to a general stress response that involves the activation of antioxidant defense pathways to restore redox balance. Further, I studied a 3-gene cluster, pefRCD (porphyrin-regulated efflux RCD), which was activated by environmental heme, and provided support to my hypothesis that the pefRCD gene encodes a heme-sensing regulator (PefR) and heme efflux system (PefCD). I showed that the pef system protects GAS cells from heme-induced damage to the membrane and DNA by preventing cellular accumulation of heme. In conclusion, this dissertation addresses key knowledge gaps in GAS physiology and provides new insights into heme metabolism of GAS.

Inherited disorders of bilirubin metabolism - hereditary hyperbilirubinemias - are metabolic disorders manifested in early childhood. Unconjugated hyperbilirubinemias result from the defect of the enzyme uridine diphosphoglucuronosyltransferase (UGT1A1). UGT1A1 mediates the conjugation of bilirubin with glucuronid acid in hepatocytes and its elimination to water soluble compound. In the next step of bilirubin degradation the transport of conjugated bilirubin from hepatocyte into the bile occure. It is caused by the ATP dependent transporters ABCC2, ATP1B1 and OATP1B3. Mutations in the genes coding the bilirubin transporters results in conjugated hyperbilirubinemia Dubin-Johnson or Rotor syndrome. This study is focused on unconjugated hyperbilirubinemia in adolescents including the non-typical manifestations and the defects of ABCC2 transporter and their phenotype in humans.