Effect of Bioregulator Isatin on Protein–Protein Interactions Involving Isatin-Binding Proteins

Isatin (2,3-dioxoindol) is an endogenous low-molecular-weight nonpeptide compound with a wide spectrum of biological and pharmacological activities. It is assumed that isatin acts through isatin-binding proteins. To date, more than a hundred of these proteins are known. Having a different structure and cellular and subcellular localization, they belong to different functional groups. Using the surface plasmon resonance technology, we found earlier that isatin affected the profile of intracellular amyloid-binding proteins and changed the stability of protein complexes in the model system. In fact, this indicates the selective effect of isatin on certain protein–protein interactions (PPI) that occur primarily with the participation of isatinbinding proteins. Therefore, we had formulated the hypothesis that isatin could be a regulator of a protein interactome. This study focuses on the verification of this assumption. Size-exclusion chromatography (SEC) profile of the rat liver tissue lysate along with mass-spectrometric protein identification has revealed 20 isatinbinding proteins that participate in the formation of the protein interactome. About 65 and 25% of them are involved in the formation of multimeric protein complexes and homo/heterodimers, respectively, and only 10% are detected as single molecules. The addition of isatin had a multidirectional effect on the profile of about half of the identified isatin-binding proteins. In some cases, the formation of protein complexes was induced, while in other cases the protein complexes were dissociated. This result confirms the hypothesis of the regulatory effect of isatin on certain PPIs. The data of this work in combination with our previous results allowed us to formulate an “interactomics image” of isatin as a bioregulator, which selectively controls both the formation and dissociation of a number of protein complexes. Two new isatin-dependent proteins were found in the work. This indicates that not all potential target proteins of the regulatory effect of isatin had been previously detected. The study of the molecular mechanisms of isatin action on PPI remains a difficult but priority task for future research.