Figure 1. Detection of the conformations experienced by proteins in different conditions and of their adducts allows the reconstruction of the mechanisms occurring in cells. As an example, we show here the folding process of the mitochondrial protein Cox17 induced by Mia40 [ 7]. Cox17 is a fully unfolded protein in cytoplasm, so that it has the conformational plasticity to enter the intermembrane space of mitochondria through a translocase of the outer membrane channel. A transient complex is formed here with the Mia40 protein, thanks to the interaction of the hydrophobic residues of Mia40 (in red) and Cox17 (in blue). Mia40 induces the formation of an α‐helix on a specific region of Cox17 and of an intermolecular disulfide bond (Cys residues are shown in yellow). The next step consists of switching of the intermolecular disulfide bond to the first intramolecular disulfide bond within Cox17, so that Mia40 is released. Finally, the formation of the second α‐helix is induced by the interactions of its hydrophobic residues with the first helix and the second intramolecular disulfide bond is formed. Once the two disulfide bonds are formed, the protein, now folded, is trapped in the intermembrane space.