Characterization of the Oligomerization of Yeast Iron-Sulfur Cluster Scaffold Protein, Isu1, in the Presence and Absence of Oligomeric Frataxin Homologue, Yfh1

• Main Author: Galeano, Belinda K
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01.01.2015
• Subjects: Biochemistry; Biophysics
• ISBN: 9781339747347; 1339747340

Iron-sulfur (Fe/S) clusters are ancient co-factors with several known functions, which include Kreb’s cycle and electron transport chain metabolism, DNA synthesis and repair and regulation of iron homeostasis. Due to their significance, imbalances within Fe/S cluster related systems may result in an array of medical conditions including mitochondrial disease, muscular dystrophy, anemia and iron overload. Therefore, development of treatments for these conditions sparked efforts toward elucidating the machinery and mechanisms associated with cluster synthesis and utilization. The current paradigm of Fe/S cluster biogenesis proposes Fe/S cluster synthesis is initiated on a scaffold protein (yeast Isu1/mammalian ISCU) and involves (i) a cysteine desulfurase (yeast Nfs1/mammalian NFS1), stabilized by a small binding partner, Isd11/ISD11, that serves as the sulfur donor; (ii) frataxin (yeast Yfh1/mammalian FXN) that serves as the iron donor; and (iii) the electron donor chain formed by ferredoxin reductase and ferredoxin (yeast Arh1-Yah1/mammalian FDXR-FDX2). Subsequently, clusters are released from Isu1/ISCU and transferred to apo-enzymes by various chaperone and co-chaperones. In these models, the ISC scaffold protein, Isu1/ISCU, is thought to cycle between separate early and late components. Recent studies suggest that mitochondrial Fe/S cluster biogenesis occurs on stable complexes composed of at least four components: Nfs1, Isd11, Isu1 and Yfh1 in yeast; NFS1, ISD11, ISCU and FXN in humans. We sought to characterize the structure of these complexes. The structure of yeast Isu1 remains to be determined. A consensus on its oligomerization properties continues to be a matter of debate. We therefore sought to determine the structure of Isu1 monomer and characterize its propensity to form oligomers. Based on our understanding of the Yfh1?Isu1 complex and of Isu1 in solution, we propose that Isu1 oligomerization is normally induced by a conformational change that occurs when Isu1 binds to Yfh1 oligomer. Interaction of Yfh1 and Isu1 results in a complex that can vary in biophysical properties. We sought to characterize the different biophysical characteristics and offer an explanation for such variability.