Biogenesis of the Essential Tim9–Tim10 Chaperone Complex of Mitochondria

Abstract

The mitochondrial intermembrane space {(IMS)} contains an essential machinery for protein import and assembly {(MIA).} Biogenesis of {IMS} proteins involves a disulfide relay between precursor proteins, the cysteine-rich {IMS} protein Mia40 and the sulfhydryl oxidase Erv1. How precursor proteins are specifically directed to the {IMS} has remained unknown. Here we systematically analyzed the role of cysteine residues in the biogenesis of the essential {IMS} chaperone complex {Tim9-Tim10.} Although each of the four cysteines of Tim9, as well as of Tim10, is required for assembly of the chaperone complex, only the most amino-terminal cysteine residue of each precursor is critical for translocation across the outer membrane and interaction with Mia40. Mia40 selectively recognizes cysteine-containing {IMS} proteins in a site-specific manner in organello and in vitro. Our results indicate that Mia40 acts as a trans receptor in the biogenesis of mitochondrial {IMS} proteins.