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Heme a Biosynthesis and Trafficking in the Mitochondria
Heme is an essential molecule for many cellular functions. However, due to its labile state, tight regulation of its synthesis and trafficking is necessary to prevent the formation of harmful reactive oxygen species. While much is known regarding heme synthesis, little is known about its transport to its final destinations. Breakdown of these processes leads to a multitude of diseases. Therefore, a better understanding of heme biosynthesis and its transport is necessary to provide targeted therapeutics of these disorders. One well documented pathway of heme trafficking after its synthesis is along the heme a biosynthesis pathway. Heme a is an essential cofactor for Cytochrome c Oxidase (CcO). Without heme a, the complex is degraded, halting cellular respiration. Heme a is synthesized in a two-step process by the enzymes Heme o Synthase, Cox10, and Heme a Synthase, Cox15. Much is known regarding the oligomerization properties of Cox10, but the enzymatic properties and oligomeric state of Cox15 is less well defined. Chapter 3 identifies important residues for Cox15 catalysis, determines the necessity of Cox15 homo-oligomerization for function, and characterizes patient mutations of the protein that lead to disease. Assembly of the intact CcO is a multi-step process requiring careful coordination between the mitochondria and the nucleus. In addition to direct components of the complex, there are a multitude of accessory proteins required for proper complex assembly. One such protein is Pet117. Previous work identified Pet117 as a CcO assembly factor; however, where in the process Pet117 functions has never been determined. Chapter 4 characterizes its localization and identifies it as an important component for stabilizing Cox15 oligomers, promoting heme a biosynthesis. Despite the important findings of this work, there is still much to be determined regarding heme trafficking. The labile state of the molecule indicates it likely requires a chaperone after synthesis to its final destinations; however, this chaperone has yet to be identified. Additionally, heme transfer between components of the heme a biosynthesis pathway remains to be determined. Finally, the exact mechanisms of proteins involved in heme a biosynthesis need to be determined. The final chapter addresses these problems.
Swenson, Samantha A, "Heme a Biosynthesis and Trafficking in the Mitochondria" (2017). ETD collection for University of Nebraska-Lincoln. AAI10615310.