Calpains are a family of calcium-dependent thiol-proteases that act on a wide variety of cytoskeletal, membrane-associated, and regulatory proteins. There are two major isoforms: calpain I (µ-form) and calpain II (m-form), which differ in their calcium requirement for activation Calpains are composed of heterodimers of 80 kDa and a 30 kDa subunits. The 80 kDa unit has the catalytic site and is unique to each isozyme, whereas the 30 kDa unit is the regulatory subunit and is common to both µ- and m-isozymes.
More recently, attention has been focused on the pathological significance of calcium accumulation in the central nervous system following cerebral ischemia and traumatic brain injury. Over-activation of NMDA, kainate, and AMPA receptors in the brain leads to sustained influx of Ca2+ through the voltage-gated calcium channels. Overexpression of calpains has been positively linked to both acute and chronic neurodegenerative processes including ischemia, trauma, and Alzheimer′s disease. In Alzheimer′s disease the ratio of active (76 kDa) to inactive (80 kDa) µ-calpain is reported to be much higher Calpain-dependent proteolysis is usually the late-stage common pathway towards cell death induced by excitotoxic compounds, hence, a selective inhibition of calpains to limit neuronal damage appears to be a viable therapeutic measure.
Johnson, G.V.W., and Guttmann, R.P. 1997. BioEssays19, 1011.
Kampfl, A., et al. 1997. J. Neurotauma14, 121.
Sorimachi, H., et al., 1997. Biochem. J.328, 721.
Bartus, R.T., et al. 1995. Neurol. Res.17, 249.
Wang, K.K.W., and Yuen, P-W. 1994. Trends Pharmacol. Sci.15, 412.
Saito, K., et al. 1993. Proc. Natl. Acad. Sci. USA90, 2628.
Goll, D.E., et al. 1992. BioEssays14, 549.