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EC number3.4.22.53
CAS number702693-80-9
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Calpain-2 (EC, calcium-activated neutral protease II, m-calpain, milli-calpain) is an intracellular heterodimeric calcium-activated cysteine protease.[1][2] This enzyme catalyses the following chemical reaction

Broad endopeptidase specificity

This enzyme belongs to the peptidase family C2. It is one of 15 proteins in the calpain family.[3]


Calpain-2 is a heterodimer of a catalytic subunit encoded by CAPN2 gene and a regulatory subunit CAPNS1.[1][4][5] The catalytic subunit consists of four domains: protease core 1 domain (PC1), protease core 2 domain (PC2), calpain-type beta-sandwich-like domain (CBSW), and penta EF-hand domain (PEF(L)).[3] The catalytic cleft is formed by PC1 and PC2 upon calcium binding.[6] The catalytic triad consists of residues C105, H262, and N286. Noteworthy, CAPN2 also contains an N-terminal anchor helix, which however is cleaved off upon protease activation.[7] It is believed to play a role in a regulation of catalytic activity.

The regulatory subunit consists of two domains: a glycine-rich domain (GR), and penta EF-hand domain (PEF(S))[3]. The interaction of PEF(S) and PEF(L) through an unpaired EF-hand motif causes dimerization of the two subunits. Calpain-2 heterodimer is highly homologous to calpain-1, which is formed by a catalytic CAPN1 and a regulatory CAPNS1 subunits.[3]


There is no known consensus sequence for calpain-2 proteolysis, but there is evidence for over 130 potential substrates.[8] Proteolytic cleavage by calpain-2 is regulated by presence of Ca2+ ions. It requires supraphysiological (low millimolar) concentration of Ca2+ for activation.[6] Intracellular concentration of Ca2+ (approx. 100 nM)[9] is insufficient for activating calpain-2, so activation occurs upon influx of ions from extracellular space or from endoplasmic reticulum. In addition, calpain-1/2 can be inhibited by calpastatin (encoded by the CAST gene) which binds to the PEF domains of the catalytic and regulatory subunits of calpains-1/2. It prohibits substrate binding to the active site through steric hindrance.[10]

Calpain-2 in Cancer

Upregulation of calpain-2 is linked to increased aggressiveness of cancer. [11][12] There is evidence suggesting that the mechanism of action is through cleavage of substrates involved in cell migration, invasion, and sensitivity to chemotherapeutic agents.[13][14][15]

Domain Nomenclature

Previously used nomenclature used Roman numerals to denote calpain-2 domains starting from the N-terminus of CAPN2 and ending at C-terminus of CAPNS1. For example, PEF(L) and PEF(S) were referred to as Domain IV and Domain VI, respectively.[16]

See also


  1. 1.0 1.1 "The crystal structure of calcium-free human m-calpain suggests an electrostatic switch mechanism for activation by calcium". Proceedings of the National Academy of Sciences of the United States of America 97 (2): 588–92. January 2000. doi:10.1073/pnas.97.2.588. PMID 10639123. Bibcode2000PNAS...97..588S. 
  2. "Origins of the difference in Ca2+ requirement for activation of mu- and m-calpain". The Biochemical Journal 367 (Pt 1): 263–9. October 2002. doi:10.1042/bj20020485. PMID 12014988. 
  3. 3.0 3.1 3.2 3.3 "Calpains: an elaborate proteolytic system". Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics 1824 (1): 224–36. January 2012. doi:10.1016/j.bbapap.2011.08.005. PMID 21864727. 
  4. "Crystal structure of calpain reveals the structural basis for Ca(2+)-dependent protease activity and a novel mode of enzyme activation". The EMBO Journal 18 (24): 6880–9. December 1999. doi:10.1093/emboj/18.24.6880. PMID 10601010. 
  5. "m-Calpain subunits remain associated in the presence of calcium". FEBS Letters 436 (3): 367–71. October 1998. doi:10.1016/s0014-5793(98)01167-3. PMID 9801150. 
  6. 6.0 6.1 "A Ca(2+) switch aligns the active site of calpain" (in English). Cell 108 (5): 649–60. March 2002. doi:10.1016/S0092-8674(02)00659-1. PMID 11893336. 
  7. "m-Calpain activation in vitro does not require autolysis or subunit dissociation". Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics 1814 (7): 864–72. July 2011. doi:10.1016/j.bbapap.2011.04.007. PMID 21549862. 
  8. "GPS-CCD: a novel computational program for the prediction of calpain cleavage sites". PLOS ONE 6 (4): e19001. April 2011. doi:10.1371/journal.pone.0019001. PMID 21533053. Bibcode2011PLoSO...619001L. 
  9. "Extracellular calcium as an integrator of tissue function". The International Journal of Biochemistry & Cell Biology 40 (8): 1467–80. 2008. doi:10.1016/j.biocel.2008.01.019. PMID 18328773. 
  10. "Calcium-bound structure of calpain and its mechanism of inhibition by calpastatin". Nature 456 (7220): 409–12. November 2008. doi:10.1038/nature07451. PMID 19020623. Bibcode2008Natur.456..409H. 
  11. "The calpain system and cancer". Nature Reviews. Cancer 11 (5): 364–74. May 2011. doi:10.1038/nrc3050. PMID 21508973. 
  12. "Calpain-2 expression is associated with response to platinum based chemotherapy, progression-free and overall survival in ovarian cancer". Journal of Cellular and Molecular Medicine 16 (10): 2422–8. October 2012. doi:10.1111/j.1582-4934.2012.01559.x. PMID 22435971. 
  13. "Regulating cell migration: calpains make the cut". Journal of Cell Science 118 (Pt 17): 3829–38. September 2005. doi:10.1242/jcs.02562. PMID 16129881. 
  14. "Calpain Genetic Disruption and HSP90 Inhibition Combine To Attenuate Mammary Tumorigenesis". Molecular and Cellular Biology 36 (15): 2078–88. August 2016. doi:10.1128/MCB.01062-15. PMID 27215381. 
  15. "Genetic disruption of calpain-1 and calpain-2 attenuates tumorigenesis in mouse models of HER2+ breast cancer and sensitizes cancer cells to doxorubicin and lapatinib". Oncotarget 9 (70): 33382–33395. September 2018. doi:10.18632/oncotarget.26078. PMID 30279968. 
  16. "Structure and nomenclature / Calpain Research Portal: Calpain Structure and Nomenclature". 

External links