1df0
CRYSTAL STRUCTURE OF M-CALPAIN
OverviewOverview
The combination of thiol protease activity and calmodulin-like EF-hands is a feature unique to the calpains. The regulatory mechanisms governing calpain activity are complex, and the nature of the Ca(2+)-induced switch between inactive and active forms has remained elusive in the absence of structural information. We describe here the 2.6 A crystal structure of m-calpain in the Ca(2+)-free form, which illustrates the structural basis for the inactivity of calpain in the absence of Ca(2+). It also reveals an unusual thiol protease fold, which is associated with Ca(2+)-binding domains through heterodimerization and a C(2)-like beta-sandwich domain. Strikingly, the structure shows that the catalytic triad is not assembled, indicating that Ca(2+)-binding must induce conformational changes that re-orient the protease domains to form a functional active site. The alpha-helical N-terminal anchor of the catalytic subunit does not occupy the active site but inhibits its assembly and regulates Ca(2+)-sensitivity through association with the regulatory subunit. This Ca(2+)-dependent activation mechanism is clearly distinct from those of classical proteases.
About this StructureAbout this Structure
1DF0 is a Protein complex structure of sequences from Rattus norvegicus. Full crystallographic information is available from OCA.
ReferenceReference
Crystal structure of calpain reveals the structural basis for Ca(2+)-dependent protease activity and a novel mode of enzyme activation., Hosfield CM, Elce JS, Davies PL, Jia Z, EMBO J. 1999 Dec 15;18(24):6880-9. PMID:10601010 Page seeded by OCA on Fri May 2 13:46:38 2008