title: Brain fodrin: substrate for calpain I, an endogenous calcium-activated protease.
abstract: The calcium-activated thiol-protease calpain I, which is present in cytosolic and membrane preparations from rat brain, was tested for its capacity to degrade the neuronal spectrin-like protein fodrin. In the presence of micromolar calcium concentrations purified calpain I degraded both purified fodrin and the fodrin present in hippocampal and cerebellar membranes. Fodrin was identified as a high molecular weight protein present in brain membranes by the following criteria: (i) comigration on NaDodSO4/polyacrylamide gels with purified fodrin, (ii) reactivity with antibodies to purified fodrin, and (iii) a proteolytic map following calpain activation comparable to that found after calpain-mediated degradation of purified fodrin. The fodrin breakdown was selective in that calpain I did not affect at least 15 other membrane-associated polypeptides. Fodrin degradation by the protease was rapid and was accompanied by the appearance of a lower molecular weight breakdown product. Calpain I had a high affinity for fodrin, with a Km for degradation of about 50 nM. Purified calpain I also degraded purified spectrin and the spectrin present in erythrocyte membranes. Calpain I-mediated degradation of spectrin-like proteins could provide a mechanism by which brief increases in intracellular free calcium levels modify the structure of the submembraneous cytoskeleton and the distribution of cell surface receptors and alter cell shape.
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D002154:Calpain; D002352:Carrier Proteins / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008840:Microfilament Proteins; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009441:Neurilemma / Q000378:metabolism; D011480:Protease Inhibitors; D051381:Rats; D013049:Spectrin / Q000378:metabolism*
chemical_list: D002118:Calcium; D002154:Calpain; D002352:Carrier Proteins; D010450:Endopeptidases; D008565:Membrane Proteins; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D011480:Protease Inhibitors; D013049:Spectrin