A proteasome activator subunit binds calcium.
We recently cloned a cDNA encoding the 29-kDa subunit of human red blood cell regulator (REG), a potent activator of the multicatalytic protease (Realini, C., Dubiel, W., Pratt, G., Ferrell, K., and Rechsteiner, M. (1994) J. Biol. Chem. 269, 20727-20732). The sequence of this subunit contains 28 "alternating" lysine and glutamic acid residues (a KEKE motif). Similar regions are present in a number of Ca(2+)-binding proteins, and using standard filter assays, the recombinant protein is shown to bind 45Ca2+ and ruthenium red. 45Ca2+ is also bound to a ubiquitin extension protein containing the 28-residue KEKE region from the 29-kDa REG subunit. Thus, the 29-kDa REG subunit is a Ca(2+)-binding protein, and its KEKE region is able to bind divalent cations. Ca2+ reversibly inhibits the enhanced peptidase activity of complexes between the multicatalytic protease and recombinant REG. This raises the possibility that multicatalytic protease activity is regulated by calcium in vivo.
Department of Biochemistry, University of Utah School of Medicine, Salt Lake City 84132, USA.
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Realini
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Rechsteiner
D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D004912:Erythrocytes / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011506:Proteins / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism
D002135:Calcium-Binding Proteins; D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D011506:Proteins; D011994:Recombinant Proteins; C088683:multicatalytic protease activator; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008274:Magnesium; D002118:Calcium