The crystal structure of calcium-free human m-calpain suggests an electrostatic switch mechanism for activation by calcium.
Strobl, S., Fernandez-Catalan, C., Braun, M., Huber, R., Masumoto, H., Nakagawa, K., Irie, A., Sorimachi, H., Bourenkow, G., Bartunik, H., Suzuki, K., Bode, W.(2000) Proc Natl Acad Sci U S A 97: 588-592
- PubMed: 10639123 
- DOI: 10.1073/pnas.97.2.588
- Primary Citation of Related Structures:  
1KFU, 1KFX - PubMed Abstract: 
Calpains (calcium-dependent cytoplasmic cysteine proteinases) are implicated in processes such as cytoskeleton remodeling and signal transduction. The 2.3-A crystal structure of full-length heterodimeric [80-kDa (dI-dIV) + 30-kDa (dV+dVI)] human m-calpain crystallized in the absence of calcium reveals an oval disc-like shape, with the papain-like catalytic domain dII and the two calmodulin-like domains dIV+dVI occupying opposite poles, and the tumor necrosis factor alpha-like beta-sandwich domain dIII and the N-terminal segments dI+dV located between ...