Defining the role of cytosolic iron-sulfur cluster assembly targeting complex in identification of iron-sulfur cluster proteins
Vo, Amanda T.
MetadataShow full item record
Iron sulfur (FeS) clusters are ubiquitous cofactors required for numerous fundamental biochemical processes, including DNA replication and repair, transcription, and translation. In the cell, these metallocofactors require a dedicated protein pathway for assembly. The Cytosolic Iron Sulfur Cluster Assembly (CIA) pathway is conserved across higher-level eukaryotes and is responsible for building and inserting these cofactors into the FeS proteins that need them. A major unsolved problem in the FeS cluster biogenesis field is how so many diverse FeS proteins are identified for cluster insertion. Several studies have identified a multiprotein complex containing Cia1, Cia2, and Met18 as the CIA targeting complex responsible for FeS cluster recognition and target maturation. The CIA targeting complex has been shown to associate with an FeS cluster protein, Nar1. Nar1 is a CIA factor that plays an unknown role in cluster transfer. Little information is known about the structure of the CIA targeting complex its mechanism of FeS cluster protein recognition. In this thesis, I investigate the architecture of the CIA targeting complex as well as the role each subunit plays in identification of apo-proteins and iron-sulfur cluster insertion. Previous proteomic and cell biological studies from the Lill lab propose that the CIA targeting complex exists as a mixture of discrete complexes in vivo. Each of these complexes is responsible for recognizing a distinct subset of targets. Herein, we utilize affinity co-purification and size exclusion chromatography investigate connectivity of the targeting complex, identify stable subcomplexes, and define their roles in recognizing our two model targets Rad3 and Leu1. We determine the CIA targeting complex contains one Met18, two Cia1, and four Cia2 polypepides. This complex is required to recognize Leu1. Our experiments reveal the formation of the stable subcomplexes Cia1-Cia2 and Met18-Cia2, which is sufficient to identify to Rad3. We also interrogate the role of Nar1 in binding to targets and cluster transfer, excluding the model that it acts as an adapter for cluster transfer. Furthermore, using site directed mutagenesis, combined with our co-purification and in vivo assays, we map the key interfaces required to form the targeting complex and investigate how their mutations impacts CIA function in vivo. We identify the binding site of Cia1 on Cia2, as well as the general region in which Cia2 binds to Met18. Through these experiments, we shed light on the role these subunits of CIA targeting complex and Nar1 play in FeS target recognition and FeS cluster transfer.
RightsAttribution-NonCommercial-NoDerivatives 4.0 International