title: [Characterization of the extracellular proteasomes and its interacting proteins by iTRAQ mass spectrometry].
abstract: The analysis of the extracellular proteasomes by isobaric tagging for relative and absolute quantifications (iTRAQ) mass spectrometry has been carried out. Here we show a standard set of 26S proteasomal subunits in the composition of the extracellular proteasomes. Moreover, extracellular proteasomes have a number of PA200 activators, which, as previously thought, are localized in the cell nucleus. Posttranslational modifications (PTMs) of subunits of the extracellular proteasomes were revealed by iTRAQ mass spectrometry. For the first time we have identified several ubiquitination and acetylation sites on subunits alpha2 (K196), alpha4 (K189 and K234), alpha6 (K217), and Rpn6 (A2). We have revealed a large number of proteasome-interacting proteins that are involved in various cell processes, such as transcription, DNA repair, translation, cytoskeletal proteins and the proteins of the ubiquitin-proteasome system (UPS). Immunoblot analysis has confirmed the interactions between purified extracellular proteasomes and nine proteins which were randomly selected from the set of interacting proteins.
authors.forename: Iu Ia
authors.initials: IuIa
authors.lastname: Zaĭkova
authors.forename: V A
authors.initials: VA
authors.lastname: Kulichkova
authors.forename: Iu B
authors.initials: IuB
authors.lastname: Ermolaeva
authors.forename: A
authors.initials: A
authors.lastname: Bottrill
authors.forename: N A
authors.initials: NA
authors.lastname: Barlev
authors.forename: A S
authors.initials: AS
authors.lastname: Tsimokha
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D013058:Mass Spectrometry; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000145:classification / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D025801:Ubiquitin / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D009687:Nuclear Proteins; D046988:Proteasome Endopeptidase Complex; D025801:Ubiquitin; C521188:PSME4 protein, human; C061553:ATP dependent 26S protease