Characterization of a caldesmon fragment that competes with myosin-ATP binding to actin.

AUTOR(ES)

Velaz, L

RESUMO

The protein caldesmon inhibits actin-activated ATP hydrolysis of myosin and inhibits the binding of myosin.ATP to actin. A fragment isolated from a chymotryptic digest of caldesmon contains features of the intact molecule that make it useful as a selective inhibitor of the binding of myosin.ATP complexes to actin without having the complexity of binding to myosin. The COOH-terminal 20 kDa region of caldesmon binds to actin with one-sixth the affinity of caldesmon with a stoichiometry of binding of one fragment per two actin monomers. This contrasts with the 1:6-9 stoichiometry of intact caldesmon. The binding of the 20 kDa fragments to actin is totally reversed by Ca(2+)-calmodulin and, like intact caldesmon, the 20 kDa fragments are competitive with the binding of myosin subfragments to actin. This competition with myosin binding is largely responsible for the inhibition of ATP hydrolysis, although both the fragments and intact caldesmon also reverse the potentiation of ATPase activity caused by tropomyosin. These polypeptides are useful both in defining the function of caldesmon and in studying the role of weakly bound cross-bridges in muscle.

Documentos Relacionados

• ATP binding to a protease-resistant core of actin.
• Photolysis of a photolabile precursor of ATP (caged ATP) induces microsecond rotational motions of myosin heads bound to actin.
• Purification and characterization of caldesmon77: a calmodulin-binding protein that interacts with actin filaments from bovine adrenal medulla.
• Both N-terminal myosin-binding and C-terminal actin-binding sites on smooth muscle caldesmon are required for caldesmon-mediated inhibition of actin filament velocity
• Caldesmon and a 20-kDa actin-binding fragment of caldesmon inhibit tension development in skinned gizzard muscle fiber bundles.