Fe–S Cluster Hsp70 Chaperones: The ATPase Cycle and Protein Interactions

Abstract

Hsp70 chaperones and their obligatory J-protein cochaperones function together in many cellular processes. Via cycles of binding to short stretches of exposed amino acids on substrate proteins, Hsp70/J-protein chaperones not only facilitate protein folding but also drive intracellular protein transport, biogenesis of cellular structures, and disassembly of protein complexes. The biogenesis of iron–sulfur (Fe–S) clusters is one of the critical cellular processes that require Hsp70/J-protein action. Fe–S clusters are ubiquitous cofactors critical for activity of proteins performing diverse functions in, for example, metabolism, RNA/DNA transactions, and environmental sensing. This biogenesis process can be divided into two sequential steps: first, the assembly of an Fe–S cluster on a conserved scaffold protein, and second, the transfer of the cluster from the scaffold to a recipient protein. The second step involves Hsp70/J-protein chaperones. Via binding to the scaffold, chaperones enable cluster transfer to recipient proteins. In eukaryotic cells mitochondria have a key role in Fe–S cluster biogenesis. In this review, we focus on methods that enabled us to dissect protein interactions critical for the function of Hsp70/J-protein chaperones in the mitochondrial process of Fe–S cluster bio-genesis in the yeast Saccharomyces cerevisiae.

SSR1 is a vital regulator in plant mitochondrial iron-sulfur biosynthesis

“…All these data clearly indicate HSCA1 and HSCA2 are functionally redundant, at least in controlling root development under normal growth conditions. This also agrees with the common view that, after the duplication event of certain mitochondrial HSP70 gene, one copy, HSCA1 in Arabidopsis, is the predominant form and plays a multifaceted role, while the paralog HSCA2 becomes an isoform only for the ISC pathway (Dutkiewicz et al, 2017).…”

“…In bacteria, five core proteins have been identified: IscS, IscU, Fdx, HscB and HscA (Roche et al, 2013). The yeast homologs are Nfs1, Isu1, Yfh1, Jac1, and Ssq1 (Barras et al, 2005; Dutkiewicz et al, 2017). During the Fe-S assembling stage, IscS/Nfs1 catalyzes the release of sulfur from L-cysteine and transfers it to the scaffold protein IscU/Isu1, where Fe-S clusters are assembled (Smith et al, 2001; Urbina et al, 2001; Cupp-Vickery et al, 2003; Smith et al, 2005).…”

“…HscA/Ssq1 recognizes the LPPVK motif in IscU/Isu1 to form a protein complex together with apoproteins (Hoff et al, 2003; Cupp-Vickery et al, 2004). IscU/Isu undergoes a conformation change to facilitate the release of Fe-S cluster from IscU/Isu1 (Kim et al, 2012; Balk and Schaedler, 2014; Dutkiewicz et al, 2017). This process is energized by HscA ATP hydrolysis, which is generally stimulated by the binding of HscB/Jac1 and/or IscU/Isu1 (Dutkiewicz et al, 2004; Kim et al, 2012; Majewska et al, 2013; Leaden et al, 2014).…”

The SUF system: an ABC ATPase-dependent protein complex with a role in Fe–S cluster biogenesis

“…SufC), while the ISC system depends on ATP-using DnaK/J-like chaperones (i.e. HscA and HscB) [13,25]. In E. coli, SUF acts as a back-up system when the ISC system is unable to sustain cellular FeeS demand.…”

NMR as a Tool to Investigate the Processes of Mitochondrial and Cytosolic Iron-Sulfur Cluster Biosynthesis

“…Both ISCU and HSC20 simulate the ATPase activity. ATP hydrolysis induces a conformational change of HSP70, and ISCU undergoes a conformation change (likely from the S- to the D-state) that makes its “LPPVK” loop accessible to HSP70 and stimulates release of the [2Fe-2S] cluster to a recipient protein [ 167 , 177 ]. The nucleotide exchange factor (NEF) then binds to HSP70 and catalyzes the exchange of ADP for ATP to set up the subsequent cycle [ 178 ].…”