PR00704

CALPAIN

PRINTS entry
Member databasePRINTS
PRINTS typefamily
Short nameCALPAIN

Description
Imported from IPR022684

This group of cysteine peptidases belong to the MEROPS peptidase family C2 (calpain family, clan CA). A type example is calpain, which is an intracellular protease involved in many important cellular functions that are regulated by calcium
[2, 5, 10, 11]
. The protein is a complex of 2 polypeptide chains (light and heavy), with eleven known active peptidases in humans and two non-peptidase homologues known as calpamodulin and androglobin
[3]
. These include a highly calcium-sensitive (i.e., micro-molar range) form known as mu-calpain, mu-CANP or calpain I; a form sensitive to calcium in the milli-molar range, known as m-calpain, m-CANP or calpain II; and a third form, known as p94, which is found in skeletal muscle only
[9]
.

All forms have identical light but different heavy chains. Both mu- and m-calpain are heterodimers containing an identical 28kDa subunit and an 80kDa subunit that shares 55-65% sequence homology between the two proteases
[6, 2]
. The crystallographic structure of m-calpain reveals six "domains" in the 80kDa subunit
[8, 4]
:

     * A 19-amino acid NH2-terminal sequence;
     * Active site domain IIa;
     * Active site domain IIb. Domain 2 shows low levels of sequence similarity to papain; although the catalytic His has not been located by biochemical means, it is likely that calpain and papain are related
[6]
.
 * Domain III;
 * An 18-amino acid extended sequence linking domain III to domain IV;
 * Domain IV, which resembles the penta EF-hand family of polypeptides, binds calcium and regulates activity
[6]
. Ca2+-binding causes a rearrangement of the protein backbone, the net effect of which is that a Trp side chain, which acts as a wedge between catalytic domains IIa and IIb in the apo state, moves away from the active site cleft allowing for the proper formation of the catalytic triad
[1]
.

Calpain-like mRNAs have been identified in other organisms including bacteria, but the molecules encoded by these mRNAs have not been isolated, so little is known about their properties. How calpain activity is regulated in these organisms cells is still unclear In metazoans, the activity of calpain is controlled by a single proteinase inhibitor, calpastatin (
IPR001259
). The calpastatin gene can produce eight or more calpastatin polypeptides ranging from 17 to 85kDa by use of different promoters and alternative splicing events. The physiological significance of these different calpastatins is unclear, although all bind to three different places on the calpain molecule; binding to at least two of the sites is Ca2+ dependent. The calpains ostensibly participate in a variety of cellular processes including remodelling of cytoskeletal/membrane attachments, different signal transduction pathways, and apoptosis. Deregulated calpain activity following loss of Ca2+ homeostasis results in tissue damage in response to events such as myocardial infarcts, stroke, and brain trauma
[7]
.

References
Imported from IPR022684

1.How calpain is activated by calcium. Khorchid A, Ikura M. Nat. Struct. Biol. 9, 239-41, (2002). View articlePMID: 11914728

2.Tandemly reiterated negative enhancer-like elements regulate transcription of a human gene for the large subunit of calcium-dependent protease. Hata A, Ohno S, Akita Y, Suzuki K. J. Biol. Chem. 264, 6404-11, (1989). View articlePMID: 2539381

3.Calpains: an elaborate proteolytic system. Ono Y, Sorimachi H. Biochim. Biophys. Acta 1824, 224-36, (2012). View articlePMID: 21864727

4.The structure of calpain. Sorimachi H, Suzuki K. J. Biochem. 129, 653-64, (2001). View articlePMID: 11328585

5.Structural basis for possible calcium-induced activation mechanisms of calpains. Reverter D, Strobl S, Fernandez-Catalan C, Sorimachi H, Suzuki K, Bode W. Biol. Chem. 382, 753-66, (2001). View articlePMID: 11517928

6.Families of cysteine peptidases. Rawlings ND, Barrett AJ. Meth. Enzymol. 244, 461-86, (1994). View articlePMID: 7845226

7.The calpain system. Goll DE, Thompson VF, Li H, Wei W, Cong J. Physiol. Rev. 83, 731-801, (2003). View articlePMID: 12843408

8.Structure and physiological function of calpains. Sorimachi H, Ishiura S, Suzuki K. Biochem. J. 328 ( Pt 3), 721-32, (1997). View articlePMID: 9396712

9.Molecular cloning of a novel mammalian calcium-dependent protease distinct from both m- and mu-types. Specific expression of the mRNA in skeletal muscle. Sorimachi H, Imajoh-Ohmi S, Emori Y, Kawasaki H, Ohno S, Minami Y, Suzuki K. J. Biol. Chem. 264, 20106-11, (1989). View articlePMID: 2555341

10.Cutting to the chase: calpain proteases in cell motility. Glading A, Lauffenburger DA, Wells A. Trends Cell Biol. 12, 46-54, (2002). View articlePMID: 11854009

11.Calpain. Perrin BJ, Huttenlocher A. Int. J. Biochem. Cell Biol. 34, 722-5, (2002). View articlePMID: 11950589

Supplementary References

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