Calmodulin and calcium-dependent protease I coordinately regulate the interaction of fodrin with actin.
The calcium-dependent proteolysis of fodrin has been implicated in the regulation of secretion, neutrophil and platelet activation, and long-term potentiation in neurons. In vitro studies indicate that calcium-dependent protease I (calpain I) cleaves fodrin in the middle of the alpha subunit and in the COOH-terminal third of the beta subunit. Cleavage at the beta site requires calmodulin, which binds with high affinity to a single site in the alpha subunit. In vitro binding assays, nondenaturing gel electrophoresis, and velocity sedimentation identify a linkage between calcium-dependent protease I proteolysis of fodrin and the ability of calmodulin to regulate the self-association of fodrin and its interaction with actin. Three functional states appear to exist: (i) intact fodrin, which constitutively forms tetramers and binds F-actin; (ii) alpha-cleaved fodrin, which loses its ability to self-associate and bind F-actin in the presence of calmodulin; and (iii) alpha,beta-cleaved fodrin, a form that is incompetent to establish tetramers or bind actin. Because actin binding and fodrin self-association occur at opposite ends of the molecule, whereas calmodulin binds at its center, these results indicate that long-range interactions exist within fodrin. They also offer an example of how two calcium-dependent regulatory processes may act synergistically to reversibly regulate a linkage between the membrane and the cytoskeleton.
Harris
A S
AS
Department of Pathology, Yale University School of Medicine, New Haven, CT 06510.
Morrow
J S
JS
D000199:Actins / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism; D002147:Calmodulin / Q000494:pharmacology; D002154:Calpain / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D006706:Homeostasis; D046911:Macromolecular Substances; D008840:Microfilament Proteins / Q000378:metabolism*; D008961:Models, Structural; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D011485:Protein Binding; D013049:Spectrin
D000199:Actins; D002147:Calmodulin; D002154:Calpain; D002352:Carrier Proteins; D046911:Macromolecular Substances; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D013049:Spectrin