Oligomeric yeast frataxin drives assembly of core machinery for mitochondrial iron-sulfur cluster synthesis.
Mitochondrial biosynthesis of iron-sulfur clusters (ISCs) is a vital process involving the delivery of elemental iron and sulfur to a scaffold protein via molecular interactions that are still poorly defined. Analysis of highly conserved components of the yeast ISC assembly machinery shows that the iron-chaperone, Yfh1, and the sulfur-donor complex, Nfs1-Isd11, directly bind to each other. This interaction is mediated by direct Yfh1-Isd11 contacts. Moreover, both Yfh1 and Nfs1-Isd11 can directly bind to the scaffold, Isu1. Binding of Yfh1 to Nfs1-Isd11 or Isu1 requires oligomerization of Yfh1 and can occur in an iron-independent manner. However, more stable contacts are formed when Yfh1 oligomerization is normally coupled with the binding and oxidation of Fe2+. Our observations challenge the view that iron delivery for ISC synthesis is mediated by Fe2+-loaded monomeric Yfh1. Rather, we find that the iron oxidation-driven oligomerization of Yfh1 promotes the assembly of stable multicomponent complexes in which the iron donor and the sulfur donor simultaneously interact with each other as well as with the scaffold. Moreover, the ability to store ferric iron enables oligomeric Yfh1 to adjust iron release depending on the presence of Isu1 and the availability of elemental sulfur and reducing equivalents. In contrast, the use of anaerobic conditions that prevent Yfh1 oligomerization results in inhibition of ISC assembly on Isu1. These findings suggest that iron-dependent oligomerization is a mechanism by which the iron donor promotes assembly of the core machinery for mitochondrial ISC synthesis.
Li
Hongqiao
H
Departments of Pediatric and Adolescent Medicine and Biochemistry and Molecular Biology, Mayo Clinic, College of Medicine, Rochester, Minnesota 55905.
Gakh
Oleksandr
O
Departments of Pediatric and Adolescent Medicine and Biochemistry and Molecular Biology, Mayo Clinic, College of Medicine, Rochester, Minnesota 55905.
Smith
Douglas Y
DY
Departments of Pediatric and Adolescent Medicine and Biochemistry and Molecular Biology, Mayo Clinic, College of Medicine, Rochester, Minnesota 55905.
Isaya
Grazia
G
Departments of Pediatric and Adolescent Medicine and Biochemistry and Molecular Biology, Mayo Clinic, College of Medicine, Rochester, Minnesota 55905.
D002850:Chromatography, Gel; D004247:DNA / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D015966:Gene Expression Regulation, Fungal; D007501:Iron / Q000737:chemistry; D033862:Iron-Binding Proteins / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000737:chemistry*; D008954:Models, Biological; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry*; D013466:Sulfurtransferases / Q000737:chemistry*; D013997:Time Factors; D000096923:Frataxin
D004247:DNA; D007501:Iron; D033862:Iron-Binding Proteins; D007506:Iron-Sulfur Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; D013466:Sulfurtransferases; D000096923:Frataxin; C508374:Isd11 protein, S cerevisiae; C115912:NFS1 protein, S cerevisiae