UBIQUITIN SUBPROTEOME OF BRAIN MITOCHONDRIA AND ITS CHANGES INDUCED BY EXPERIMENTAL PARKINSONISM AND THE NEUROPROTECTOR ACTION
Own and literature data on the ubiquitination of brain mitochondrial proteins and its changes during the development of experimental parkinsonism and administration of the neuroprotector isatin (indole-2,3-dione) have been summarized. Special attention has been paid to the mitochondrial ubiquitin-conjugating system and localization of ubiquitinated proteins in mitochondria. Incubation of brain mitochondrial fraction in vitro with biotinylated ubiquitin resulted in incorporation of biotinylated ubiquitin both in mitochondrial and mitochondria-associated proteins. According to the interactome analysis, the identified non-ubiquitinated proteins are able to form tight complexes with ubiquitinated proteins or their partners and components of mitochondrial membranes. Studies of endogenous ubiquitination in the total brain mitochondrial fraction of C57Bl mice, performed in different laboratories, have shown that mitochondrial ubiquitinated proteins represented about 30% of all ubiquitinated proteins in brain. However, subproteomes of brain mitochondrial ubiquitinated proteins significantly differed both in their composition and involvement of identified ubiquitinated proteins in the biological processes listed in the Gene Ontology database. Development in C57Bl mice of experimental parkinsonism after single administration of 1-methyl-4-phenyl-1,2,3,6tetrahydropyridine (MPTP) caused (i) a decrease in the total number of brain mitochondrial ubiquitinated proteins and (ii) an increase in the number of oxidized mitochondrial proteins containing the ubiquitin signature (K-ε-GG). A comparison of the ubiquitinated proteins associated with the mouse brain mitochondrial fraction and the mouse brain mitochondrial proteins bound to the proteasome ubiquitin receptor, the Rpn10a subunit, did not reveal any common proteins. This suggests that ubiquitination of brain mitochondrial proteins is not directly related to their degradation in proteasomes. Proteomic profiling of brain isatin-binding proteins revealed enzymes involved in the ubiquitin-conjugating system functioning. Mapping the identified isatin-binding proteins to known metabolic pathways indicates their participation in the parkin (E3 ubiquitin ligase)-associated pathway (CH000000947). As for an interaction of brain mitochondrial ubiquitinated proteins, functional links were found only in a group of animals with MPTP-induced parkinsonism, but not with the administration of MPTP and isatin or only isatin. This suggests that the neuroprotective effect of isatin may be associated with impaired functional relationships of proteins that are targeted to subsequent degradation.