Calcium-Bound Structure of Calpain and its Mechanism of Inhibition by Calpastatin

Journal Article · Tue Jan 01 04:00:00 EST 2008 · Nature

DOI:https://doi.org/10.1038/nature07451· OSTI ID:980049

Hanna, R; Campbell, R; Davies, P

Calpains are non-lysosomal calcium-dependent cysteine proteinases that selectively cleave proteins in response to calcium signals and thereby control cellular functions such as cytoskeletal remodelling, cell cycle progression, gene expression and apoptotic cell death. In mammals, the two best-characterized members of the calpain family, calpain 1 and calpain 2 ({mu}-calpain and m-calpain, respectively), are ubiquitously expressed. The activity of calpains is tightly controlled by the endogenous inhibitor calpastatin, which is an intrinsically unstructured protein capable of reversibly binding and inhibiting four molecules of calpain, but only in the presence of calcium. To date, the mechanism of inhibition by calpastatin and the basis for its absolute specificity have remained speculative. It was not clear how this unstructured protein inhibits calpains without being cleaved itself, nor was it known how calcium induced changes that facilitated the binding of calpastatin to calpain. Here we report the 2.4-{angstrom}-resolution crystal structure of the calcium-bound calpain 2 heterodimer bound by one of the four inhibitory domains of calpastatin. Calpastatin is seen to inhibit calpain by occupying both sides of the active site cleft. Although the inhibitor passes through the active site cleft it escapes cleavage in a novel manner by looping out and around the active site cysteine. The inhibitory domain of calpastatin recognizes multiple lower affinity sites present only in the calcium-bound form of the enzyme, resulting in an interaction that is tight, specific and calcium dependent. This crystal structure, and that of a related complex, also reveal the conformational changes that calpain undergoes on binding calcium, which include opening of the active site cleft and movement of the domains relative to each other to produce a more compact enzyme.

• Research Organization: Brookhaven National Laboratory (BNL) National Synchrotron Light Source
• Sponsoring Organization: Doe - Office Of Science
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 980049
• Report Number(s): BNL--92967-2010-JA
• Journal Information: Nature, Journal Name: Nature Vol. 456
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
99 GENERAL AND MISCELLANEOUS
AFFINITY
CALCIUM
CELL CYCLE
CLEAVAGE
CONFORMATIONAL CHANGES
CONTROL
CRYSTAL STRUCTURE
CYSTEINE
DEATH
FUNCTIONS
GENES
INHIBITION
INTERACTIONS
MAMMALS
MOLECULES
OPENINGS
PROTEINS
SIGNALS
SPECIFICITY
national synchrotron light source