Overlapping Binding Sites of the Frataxin Homologue Assembly Factor and the Heat Shock Protein 70 Transfer Factor on the Isu Iron-Sulfur Cluster Scaffold Protein

Abstract

Background: Protein factors function in both FeS cluster assembly on and transfer from the Isu scaffold protein.Results: Common Isu residues are critical for binding both frataxin homologue (Yfh1) assembly factor and heat shock protein 70 (Hsp70) transfer factor. Conclusion: Yfh1 and Hsp70 binding is mutually exclusive. Significance: Mutual exclusive binding of assembly/transfer factors may be important in transitioning between cluster assembly and transfer.

Architecture of the Yeast Mitochondrial Iron-Sulfur Cluster Assembly Machinery

“…10B). The PVK motif (Pro-134, Val-135, and Lys-136) of Isu1 was shown to be important for Yfh1 binding in yeast (18). In our structure it is close to the Fe-S cluster assembly site, and based on both cross-linking data and PISA interface analysis, it appears to interact with both a Yfh1 subunit immediately underneath within the same [Yfh1] 3 ⅐[Isu1] 3 sub-complex, as well as an adjacent Yfh1 subunit from an opposite [Yfh1] 3 ⅐ [Isu1] 3 sub-complex (Fig.…”

“…An interface with BSA of ϳ127 Å 2 (average of 12 interfaces) between two Isu1 subunits of adjacent Isu1 trimers is formed via interactions between residues Lys-136 -Val-135 and Leu-137-Lys-136 (Fig. 8D), which are part of the highly conserved PVK motif of Isu1 (18).…”

“…On the other hand, the molecular details of iron donation from Yfh1 to Isu1 remain largely undefined. One monomer of Yfh1 was proposed to bind in a pocket between Nfs1 and Isu1 through its iron-binding surface (10,18). However, a protein docking study further suggested that Yfh1 binding would only be possible with the flexible loop of Nfs1 positioned inside the cysteine substrate-binding site rather than in proximity of the Fe-S cluster assembly site.…”

Architecture of the Human Mitochondrial Iron-Sulfur Cluster Assembly Machinery

“…The PVK motif of Isu1 was shown to be important for Isu1-Yfh1 interactions in yeast (50). In our structure, the PVK motif of ISCU is close to the Fe-S cluster assembly site and, based on both cross-linking data and PISA interface analysis, it may interact with both the flexible loop of NFS1 at a distance of ϳ7-8 Å, which contains the catalytic Cys-381, as well as with loops L4 and L6 of FXN at a distance of ϳ5 Å, which contain the iron-binding site formed by Thr-142 (loop L4) and Ser-157 (loop L6) (Fig.…”

“…The PVK motif of Isu1 is important for Yfh1-Isu1 interactions in yeast (50). The PVK motif of ISCU is close to the Fe-S cluster assembly site and may interact with both FXN subunits immediately underneath (i.e.…”