biostudies-literatureMcCartney CEGovernment of Canada Canadian Institutes of Health ResearchCIHR17716-17730https://www.ebi.ac.uk/biostudies/studies/S-EPMC6240860biostudies-literatureUnknown293(46)Calpains are intracellular, calcium-activated cysteine proteases. Calpain-3 is abundant in skeletal muscle, where its mutation-induced loss of function causes limb-girdle muscular dystrophy type 2A. Unlike the small subunit-containing calpain-1 and -2, the calpain-3 isoform homodimerizes through pairing of its C-terminal penta-EF-hand domain. It also has two unique insertion sequences (ISs) not found in the other calpains: IS1 within calpain-3's protease core and IS2 just prior to the penta-EF-hand domain. Production of either native or recombinant full-length calpain-3 to characterize the function of these ISs is challenging. Therefore, here we used recombinant rat calpain-2 as a stable surrogate and inserted IS1 into its equivalent position in the protease core. As it does in calpain-3, The Journal of biological chemistryInsertion sequence 1 from calpain-3 is functional in calpain-2 as an internal propeptide.PMC6240860MOP74681MOP 74681Davies PLCampbell RLYe QMcCartney CEfalseInsertion sequence 1 from calpain-3 is functional in calpain-2 as an internal propeptide.Calpains are intracellular, calcium-activated cysteine proteases. Calpain-3 is abundant in skeletal muscle, where its mutation-induced loss of function causes limb-girdle muscular dystrophy type 2A. Unlike the small subunit-containing calpain-1 and -2, the calpain-3 isoform homodimerizes through pairing of its C-terminal penta-EF-hand domain. It also has two unique insertion sequences (ISs) not found in the other calpains: IS1 within calpain-3's protease core and IS2 just prior to the penta-EF-hand domain. Production of either native or recombinant full-length calpain-3 to characterize the function of these ISs is challenging. Therefore, here we used recombinant rat calpain-2 as a stable surrogate and inserted IS1 into its equivalent position in the protease core. As it does in calpain-3, 2018-01-01T00:00:00Z2018 Nov2026-04-29T03:32:05.161Z2021-02-20T04:41:18ZS-EPMC62408603025407210.1074/jbc.ra118.00480310.1074/jbc.RA118.004803