title: PA28αβ reduces size and increases hydrophilicity of 20S immunoproteasome peptide products.
abstract: The specific roles that immunoproteasome variants play in MHC class I antigen presentation are unknown at present. To investigate the biochemical properties of different immunoproteasome forms and unveil the molecular mechanisms of PA28 activity, we performed in vitro degradation of full-length proteins by 20S, 26S, and PA28αβ-20S immunoproteasomes and analyzed the spectrum of peptides released. Notably, PA28αβ-20S immunoproteasomes hydrolyze proteins at the same low rates as 20S alone, which is in line with PA28, neither stimulating nor preventing entry of unfolded polypeptides into the core particle. Most importantly, binding of PA28αβ to 20S greatly reduces the size of proteasomal products and favors the release of specific, more hydrophilic, longer peptides. Hence, PA28αβ may either allosterically modify proteasome active sites or act as a selective "smart" sieve that controls the efflux of products from the 20S proteolytic chamber.
authors.affiliation: Department of Veterinary Sciences, University of Turin, 10095 Grugliasco, Italy.
authors.forename: Mary
authors.initials: M
authors.lastname: Raule
authors.affiliation: Department of Veterinary Sciences, University of Turin, 10095 Grugliasco, Italy.
authors.forename: Fulvia
authors.initials: F
authors.lastname: Cerruti
authors.affiliation: Unité Biologie des Spirochètes, Institut Pasteur, 75015 Paris, France.
authors.forename: Nadia
authors.initials: N
authors.lastname: Benaroudj
authors.affiliation: Mass Spectrometry Core Unit, Max-Delbrück Center for Molecular Medicine, 13125 Berlin, Germany.
authors.forename: Rebekka
authors.initials: R
authors.lastname: Migotti
authors.affiliation: Mass Spectrometry Core Unit, Max-Delbrück Center for Molecular Medicine, 13125 Berlin, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Kikuchi
authors.affiliation: IFOM, FIRC Institute of Molecular Oncology, 20139 Milan, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Bachi
authors.affiliation: Department of Biological Regulation, The Weizmann Institute of Science, 76100 Rehovot, Israel.
authors.forename: Ami
authors.initials: A
authors.lastname: Navon
authors.affiliation: Mass Spectrometry Core Unit, Max-Delbrück Center for Molecular Medicine, 13125 Berlin, Germany.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Dittmar
authors.affiliation: Department of Veterinary Sciences, University of Turin, 10095 Grugliasco, Italy. Electronic address: paolo.cascio@unito.it.
authors.forename: Paolo
authors.initials: P
authors.lastname: Cascio
mesh_terms: D000494:Allosteric Regulation; D020134:Catalytic Domain; D057927:Hydrophobic and Hydrophilic Interactions; D010316:Particle Size; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D053719:Tandem Mass Spectrometry
chemical_list: D046988:Proteasome Endopeptidase Complex