[The use of immobilized ubiquitin for biosensor analysis of the mitochondrial subinteractome]

Protein ubiquitination is considered as an important mechanism that is responsible not only for specific labeling of proteins for their subsequent degradation but also for localization of proteins in the cell and regulation of protein-protein interactions. In the context of protein-protein interactions binding of (mono/poly)ubiquitinated molecules to proteins containing specific ubiquitin binding domains appear to play the decisive role. Although formation of the ubiquitin interactome has been demonstrated for cytosol, involvement of mitochondria and associated extramitochondrial proteins into such interactions still requires detailed investigation. In this study using an optical biosensor we have demonstrated binding of proteins of mouse brain mitochondrial lysates to immobilized monomeric ubiquitin. Model purified proteins, which are known to be associated with the outer mitochondrial compartment (glyceraldehyde-3-phosphate dehydorgenase, creatine phosphokinase), interacted with immobilized ubiquitin as well as with each other. This suggests that (poly)ubiquitinated chains may be involved in protein-protein interactions between ubiquitinated and non-ubiquitinated proteins and thus may contribute to formation of (mitochondrial) ubiquitin subinteractome.