Concerted multi-pronged attack by calpastatin to occlude the catalytic cleft of heterodimeric calpains

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Calpains are calcium-dependent cysteine proteases regulating crucial cellular processes.
• Calpastatin is the endogenous inhibitor of calpains, essential for their regulation.
• The structural basis for calpain inhibition by calpastatin remains largely unknown.

Purpose of the Study:

• To elucidate the structural mechanism of calpain inhibition by calpastatin.
• To understand the basis of calpastatin's specificity towards calpains.

Main Methods:

• X-ray crystallography was used to determine the structure of Ca(2+)-bound m-calpain in complex with the first calpastatin repeat.
• Analysis of the protein complex structure to identify key interaction sites and conformational changes.

Main Results:

• The 3.0 Å structure reveals the Ca(2+)-bound m-calpain/calpastatin complex, detailing the mechanism of specific inhibition.
• Calcium binding induces significant conformational changes in calpain, facilitating calpastatin recognition.
• Calpastatin interacts intimately with calpain via three regions, including occupying the substrate-binding cleft.

Conclusions:

• The structure provides unprecedented insight into the molecular basis of calpain regulation by calpastatin.
• Understanding this interaction is key to comprehending calpain function in various physiological processes.
• The findings pave the way for targeted therapeutic strategies involving calpain modulation.