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.
Realini
C
C
Department of Biochemistry, University of Utah School of Medicine, Salt Lake City 84132, USA.
Rechsteiner
M
M
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