title: Beta 2 subunit propeptides influence cooperative proteasome assembly.
abstract: Vertebrate proteasomes are structurally heterogeneous, consisting of both "constitutive" (or "standard") proteasomes and "immunoproteasomes." Constitutive proteasomes contain three ubiquitously expressed catalytic subunits, Delta (beta 1), Z (beta 2), and X (beta 5), whereas immunoproteasomes contain three interferon-gamma-inducible catalytic subunits, LMP2 (beta 1i), MECL (beta 2i), and LMP7 (beta 5i). We recently have demonstrated that proteasome assembly is biased to promote immunoproteasome homogeneity when both types of catalytic subunits are expressed in the same cell. This cooperative assembly is due in part to differences between the LMP7 (beta 5i) and X (beta 5) propeptides. In the current study we demonstrate that differences between the MECL (beta 2i) and Z (beta2) propeptides also influence cooperative assembly. Specifically, replacing the MECL propeptide with that of Z enables MECL incorporation into otherwise constitutive (Delta(+)/X(+)) proteasomes and facilitates X incorporation into otherwise immunoproteasomes (MECL(+)/LMP2(+)). We also show, using MECL(-/-) mice, that LMP2 incorporation does not require MECL, in contrast with previous suggestions that their incorporation is mutually codependent. These results enable us to refine our model for cooperative proteasome assembly by determining which combinations of inducible and constitutive subunits are favored over others, and we propose a mechanism for how propeptides mediate cooperative assembly.
authors.affiliation: William S. Rowe Division of Rheumatology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA.
authors.forename: Mita
authors.initials: M
authors.lastname: De
authors.forename: Krupakar
authors.initials: K
authors.lastname: Jayarapu
authors.forename: Laura
authors.initials: L
authors.lastname: Elenich
authors.forename: John J
authors.initials: JJ
authors.lastname: Monaco
authors.forename: Robert A
authors.initials: RA
authors.lastname: Colbert
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Griffin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000172:deficiency / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D004792:Enzyme Precursors / Q000737:chemistry; D006801:Humans; D015151:Immunoblotting; D046911:Macromolecular Substances; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry*; D046988:Proteasome Endopeptidase Complex; D021122:Protein Subunits / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014714:Vertebrates
chemical_list: D018076:DNA, Complementary; D004792:Enzyme Precursors; D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D021122:Protein Subunits; D003546:Cysteine Endopeptidases; C077436:LMP7 protein; C098948:PSMB10 protein, human; D046988:Proteasome Endopeptidase Complex; C490920:Psmb10 protein, mouse