| First Author | Ono Y | Year | 2010 |
| Journal | J Biol Chem | Volume | 285 |
| Issue | 30 | Pages | 22986-98 |
| PubMed ID | 20460380 | Mgi Jnum | J:165998 |
| Mgi Id | MGI:4839427 | Doi | 10.1074/jbc.M110.126946 |
| Citation | Ono Y, et al. (2010) Skeletal muscle-specific calpain is an intracellular Na+-dependent protease. J Biol Chem 285(30):22986-98 |
| abstractText | Because intracellular [Na(+)] is kept low by Na(+)/K(+)-ATPase, Na(+) dependence is generally considered a property of extracellular enzymes. However, we found that p94/calpain 3, a skeletal-muscle-specific member of the Ca(2+)-activated intracellular 'modulator proteases' that is responsible for a limb-girdle muscular dystrophy ('calpainopathy'), underwent Na(+)-dependent, but not Cs(+)-dependent, autolysis in the absence of Ca(2+). Furthermore, Na(+) and Ca(2+) complementarily activated autolysis of p94 at physiological concentrations. By blocking Na(+)/K(+)-ATPase, we confirmed intracellular autolysis of p94 in cultured cells. This was further confirmed using inactive p94:C129S knock-in (p94CS-KI) mice as negative controls. Mutagenesis studies showed that much of the p94 molecule contributed to its Na(+)/Ca(2+)-dependent autolysis, which is consistent with the scattered location of calpainopathy-associated mutations, and that a conserved Ca(2+)-binding sequence in the protease acted as a Na(+) sensor. Proteomic analyses using Cs(+)/Mg(2+) and p94CS-KI mice as negative controls revealed that Na(+) and Ca(2+) direct p94 to proteolyze different substrates. We propose three roles for Na(+) dependence of p94; 1) to increase sensitivity of p94 to changes in physiological [Ca(2+)], 2) to regulate substrate specificity of p94, and 3) to regulate contribution of p94 as a structural component in muscle cells. Finally, this is the first example of an intracellular Na(+)-dependent enzyme. |
