Autolytic activation of calpain 3 proteinase is facilitated by calmodulin protein.
Calpains are broadly distributed, calcium-dependent enzymes that induce limited proteolysis in a wide range of substrates. Mutations in the gene encoding the muscle-specific family member calpain 3 (CAPN3) underlie limb-girdle muscular dystrophy 2A. We have shown previously that CAPN3 knockout muscles exhibit attenuated calcium release, reduced calmodulin kinase (CaMKII) signaling, and impaired muscle adaptation to exercise. However, neither the precise role of CAPN3 in these processes nor the mechanisms of CAPN3 activation in vivo have been fully elucidated. In this study, we identify calmodulin (CaM), a known transducer of the calcium signal, as the first positive regulator of CAPN3 autolytic activity. CaM was shown to bind CAPN3 at two sites located in the C2L domain. Biochemical studies using muscle extracts from transgenic mice overexpressing CAPN3 or its inactive mutant revealed that CaM binding enhanced CAPN3 autolytic activation. Furthermore, CaM facilitated CAPN3-mediated cleavage of its in vivo substrate titin in tissue extracts. Therefore, these studies reveal a novel interaction between CAPN3 and CaM and identify CaM as the first positive regulator of CAPN3 activity.
From the Department of Neurology, Geffen School of Medicine, and Center for Duchenne Muscular Dystrophy, UCLA, Los Angeles, CA 90095.
Natalia
N
Ermolova
From the Department of Neurology, Geffen School of Medicine, and Center for Duchenne Muscular Dystrophy, UCLA, Los Angeles, CA 90095.
Irina
I
Kramerova
From the Department of Neurology, Geffen School of Medicine, and Center for Duchenne Muscular Dystrophy, UCLA, Los Angeles, CA 90095 mspencer@mednet.ucla.edu.
Melissa J
MJ
Spencer
D000818:Animals; D020013:Calcium Signaling / Q000235:genetics; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000235:genetics* / Q000378:metabolism; D002147:Calmodulin / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D002154:Calpain / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D009124:Muscle Proteins / Q000096:biosynthesis / Q000235:genetics*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology; D049288:Muscular Dystrophies, Limb-Girdle / Q000235:genetics* / Q000473:pathology; D009154:Mutation; D059748:Proteolysis
D002147:Calmodulin; D009124:Muscle Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D002154:Calpain; C491373:Capn3 protein, mouse
Calmodulin (CaM); Calpain; Muscular Dystrophy; Proteinase; Skeletal Muscle