Subunit compositions and catalytic properties of proteasomes from developmental temperature- sensitive mutants of Drosophila melanogaster.
Two dominant temperature-sensitive (DTS) Drosophila mutants are missense mutations of proteasome genes encoding beta-type subunits beta6/C5 (DTS5) and beta2/Z (DTS7). At nonpermissive temperature (29 degrees C), heterozygotes (DTS5/+ and DTS7/+) develop normally until metamorphosis; pupae fail to mature and die before eclosion. Proteasomes were purified from wild-type (WT) and heterozygous adult flies raised at permissive temperature (25 degrees C). Two-dimensional gel electrophoresis separated at least 28 proteins, 13 of which were identified with monospecific antibodies to alpha6/C2 (five species), alpha2/C3 (three species), alpha7/C8 (three species), alpha5/zeta, and beta1/Y subunits. Both quantitative and qualitative differences were observed between WT and DTS/+ proteasomes, with DTS5/+ deviating more from WT than DTS7/+ proteasomes. In DTS5/+ there was a shift to more acidic species of C2 and C3 and a shift to less acidic species of 32-kDa subunits (#3-#7) recognized by an anti-alpha subunit monoclonal antibody (MCP222) and were losses of two 32-kDa subunits (#2 and #3), decreases in Y (25 kDa; 2-fold) and 31-kDa (#9; 2-fold) subunits, and increases in 52-kDa (#1; 1.9-fold) and 24-kDa (#13; 2.3-fold) subunits. In DTS7/+ there was a less pronounced shift to acidic species of C3 and no pI shift in C2 species and subunits #3-#7 and were decreases in #9 (2.5-fold) and #14 (3-fold) and a loss of #2. The three C8 species were similar between WT, DTS5/+, and DTS7/+ proteasomes. Qualitatively, the most dramatic difference was the appearance of a new 24-kDa subunit (#16) in DTS/+ preparations, with about a 14-fold greater amount of #16 in DTS7/+ than in DTS5/+ proteasomes. Catalytically, WT and DTS/+ proteasomes had similar peptidase activities, although the DTS/+ proteasomes were slightly more sensitive to SDS and elevated temperatures in vitro. The incorporation of DTS subunits apparently altered proteasome assembly and/or processing at permissive temperature with little effect on catalytic activities. These data suggest that at nonpermissive temperature, assembly/processing is more severely affected, producing DTS-containing complexes that lack functions essential for cellular proliferation and differentiation at metamorphosis.
Department of Biology, Colorado State University, Fort Collins, Colorado, 80523, USA.
J A
JA
Covi
J M
JM
Belote
D L
DL
Mykles
D000818:Animals; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D015180:Electrophoresis, Gel, Two-Dimensional; D006579:Heterozygote; D015151:Immunoblotting; D007526:Isoelectric Point; D008954:Models, Biological; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D011487:Protein Conformation; D013696:Temperature
D009097:Multienzyme Complexes; D011480:Protease Inhibitors; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex