An Intrinsically Disordered Domain Has a Dual Function Coupled to Compartment-Dependent Redox Control

The functional role of unstructured protein domains is an emerging field in the frame of intrinsically disordered proteins. The involvement of intrinsically disordered domains (IDDs) in protein targeting and biogenesis processes in mitochondria is so far not known. Here, we have characterized the structural/dynamic and functional properties of an IDD of the sulfhydryl oxidase ALR (augmenter of liver regeneration) located in the intermembrane space of mitochondria. At variance to the unfolded-to-folded structural transition of several intrinsically disordered proteins, neither substrate recognition events nor redox switch of its shuttle cysteine pair is linked to any such structural change. However, this unstructured domain performs a dual function in two cellular compartments: it acts (i) as a mitochondrial targeting signal in the cytosol and (ii) as a crucial recognition site in the disulfide relay system of intermembrane space. This domain provides an exciting new paradigm for IDDs ensuring two distinct functions that are linked to intracellular organelle targeting.