Mitochondrial Biogenesis, Switching the Sorting Pathway of the Intermembrane Space Receptor Mia40

Agnieszka Chacinska,Bernard Guiard,Judith M Müller,Agnes Schulze-Specking,Kipros Gabriel,Stephan Kutik,Nikolaus Pfanner

doi:10.1074/jbc.m805356200

Abstract

Mitochondrial precursor proteins are directed into the intermembrane space via two different routes, the presequence pathway and the redox-dependent MIA pathway. The pathways were assumed to be independent and transport different proteins. We report that the intermembrane space receptor Mia40 can switch between both pathways. In fungi, Mia40 is synthesized as large protein with an N-terminal presequence, whereas in metazoans and plants, Mia40 consists only of the conserved C-terminal domain. Human MIA40 and the C-terminal domain of yeast Mia40 (termed Mia40(core)) rescued the viability of Mia40-deficient yeast independently of the presence of a presequence. Purified Mia40(core) was imported into mitochondria via the MIA pathway. With cells expressing both full-length Mia40 and Mia40(core), we demonstrate that yeast Mia40 contains dual targeting information, directing the large precursor onto the presequence pathway and the smaller Mia40(core) onto the MIA pathway, raising interesting implications for the evolution of mitochondrial protein sorting.

Highlights

Mitochondria contain two aqueous compartments, the intermembrane space (IMS)5 and the matrix
Purified Mia40core was imported into mitochondria via the MIA pathway. With cells expressing both full-length Mia40 and Mia40core, we demonstrate that yeast Mia40 contains dual targeting information, directing the large precursor onto the presequence pathway and the smaller Mia40core onto the MIA pathway, raising interesting implications for the evolution of mitochondrial protein sorting
The preprotein is laterally transferred into the inner membrane, and the IMS domain either can be released by proteolytic cleavage or remains attached to the inner membrane via the hydrophobic segment [4, 5, 7,8,9]. (ii) Many IMS proteins are small (Ͻ15–20 kDa) and contain conserved cysteine residues that form disulfide bonds and/or bind metal ions [4, 10, 11]

Summary

Mitochondrial Protein Sorting

Mia is functional as soluble protein when it is targeted to the IMS by the bipartite signal of cytochrome b2. Grumbt et al [22] reported that a recombinant C-terminal fragment of yeast Mia is competent in binding to Erv in vitro, raising the possibility that the C-terminal domain represents a functional domain. It has not been shown if the C-terminal domain alone can bind precursor proteins and is functional in vivo. HMIA40 and Mia40core were functional in vivo, demonstrating that the C-terminal half of yeast Mia is sufficient for function and import into mitochondria. We show that Mia40core is imported into mitochondria by the MIA machinery, and yeast Mia contains dual targeting information for both the presequence and MIA pathways

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

Blocking of sulfhydryl groups of