title: The interaction of calmodulin with human erythrocyte spectrin. Inhibition of protein 4.1-stimulated actin binding.
abstract: The functional significance of calmodulin binding to human erythrocyte spectrin has been investigated under native conditions. Both native calmodulin and calmodulin derivatized with the photoactivable cross-linker methyl 4-azidobenzimidate (azidocalmodulin) have been used. When azidocalmodulin is photolyzed in the presence of erythrocyte ghosts, ghost extracts, or purified protein, it cross-links predominately to the beta subunit of erythrocyte spectrin. This cross-linking is calcium-dependent, requires photolysis, and is inhibited by 100 microM trifluoperazine or unlabeled calmodulin. Calmodulin labeled spectrin exhibits a specific and non-calcium-dependent inhibition of its ability to bind actin, even in the presence of protein 4.1. Its ability to self-associate or to bind spectrin-depleted membrane vesicles is unperturbed. Native calmodulin also inhibits protein 4.1-stimulated spectrin-actin binding, but unlike that of covalently bound calmodulin, inhibition by the uncross-linked calmodulin requires calcium. The degree of inhibition of spectrin-actin-4.1 binding induced by native calmodulin is significant since 109 microM calmodulin inhibits over 63% of the spectrin-actin binding induced by 4.5 microM protein 4.1. These results demonstrate a specific effect of calmodulin on erythroid spectrin function and suggest that calmodulin may influence the binding of protein 4.1 and actin to spectrin within the cytoskeleton.
mesh_terms: D001386:Azides / Q000378:metabolism; D001798:Blood Proteins / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000031:analogs & derivatives / Q000378:metabolism*; D003598:Cytoskeletal Proteins; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008565:Membrane Proteins; D008970:Molecular Weight; D009479:Neuropeptides; D013049:Spectrin / Q000378:metabolism*; D014268:Trifluoperazine / Q000494:pharmacology
chemical_list: D001386:Azides; D001798:Blood Proteins; D002147:Calmodulin; D003598:Cytoskeletal Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009479:Neuropeptides; C030955:azidocalmodulin; C028841:erythrocyte membrane band 4.1 protein; C120557:erythrocyte membrane protein band 4.1-like 1; D013049:Spectrin; D014268:Trifluoperazine; D002118:Calcium