Functional TIM10 chaperone assembly is redox-regulated in vivo.

The TIM10 chaperone facilitates the insertion of hydrophobic proteins at the mitochondrial inner membrane. Here we report the novel molecular mechanism of TIM10 assembly. This process crucially depends on oxidative folding in mitochondria and involves: (i) import of the subunits in a Cys-reduced and unfolded state; (ii) folding to an assembly-competent structure maintained by intramolecular disulfide bonding of their four conserved cysteines; and (iii) assembly of the oxidized zinc-devoid subunits to the functional complex. We show that intramolecular disulfide bonding occurs in vivo, whereas intermolecular disulfides observed in vitro are abortive intermediates in the assembly pathway. This novel mechanism of compartment-specific redox-regulated assembly is crucial for the formation of a functional TIM10 chaperone.