Brain Fodrin: Substrate for Calpain I, an Endogenous Calcium-Activated Protease

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 81; no. 11; pp. 3572 - 3576
• Main Authors: Siman, Robert, Baudry, Michel, Lynch, Gary
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 01.06.1984; National Acad Sciences
• Subjects: Actins; Animals; Antibodies; Brain - metabolism; Calcium; Calcium - physiology; Calpain; Carrier Proteins - metabolism; Electrophoresis; Endopeptidases - metabolism; Erythrocyte membrane; Erythrocytes; Gels; Membrane proteins; Membrane Proteins - metabolism; Microfilament Proteins; Molecular Weight; Nerve Tissue Proteins - metabolism; Neurilemma - metabolism; Neurons; Protease Inhibitors; Rats; Spectrin - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.81.11.3572

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 Kmfor degradation of about 50 nM. Purified calpain I also degraded purified spectrin and the spectrin present in erythrocyte membranes. Calpin 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.