The Rieske Iron-Sulfur Protein: Import and Assembly into the Cytochrome bc(1) Complex of Yeast Mitochondria

Abstract

The Rieske iron-sulfur protein, one of the catalytic subunits of the cytochrome bc(1) complex, is involved in electron transfer at the level of the inner membrane of yeast mitochondria. The Rieske iron-sulfur protein is encoded by nuclear DNA and, after being synthesized in the cytosol, is imported into mitochondria with the help of a cleavable N-terminal presequence. The imported protein, besides incorporating the 2Fe-2S cluster, also interacts with other catalytic and non-catalytic subunits of the cytochrome bc(1) complex, thereby assembling into the mature and functional respiratory complex. In this paper, we summarize the most recent findings on the import and assembly of the Rieske iron-sulfur protein into Saccharomyces cerevisiae mitochondria, also discussing a possible role of this protein both in the dimerization of the cytochrome bc(1) complex and in the interaction of this homodimer with other complexes of the mitochondrial respiratory chain.

Figure 1

Topology of ISP in the yeast cytochrome bc ₁ complex. (a) The arrangement of the Rieske protein in the bc ₁ complex homodimer. The subunits in the cytochrome bc ₁ dimer are depicted as ribbons, with subunits in one monomer colored grey and subunits in the other monomer colored cyan. ISPs of the two monomers are colored red. (b) Panel B shows the spatial arrangement of ISP (red) in one cytochrome bc ₁ monomer (cyan), in order to highlight its transdimeric structure.

Figure 2

Schematic model depicting the last steps of assembly of the yeast cytochrome bc ₁ complex. The 500 kDa bc ₁ subcomplex, which also includes the chaperone protein Bcs1p, sequentially binds ISP and, finally, Qcr10p, in a process which leads to the formation of the homodimeric bc ₁ complex. In the final step, supercomplexes assembly involves the sequential addition of cytochrome c oxidase complex (complex IV) to homodimeric cytochrome bc ₁ complex (complex III).