Magnesium modulates actin binding and ADP release in myosin motors.
J Biol Chem
; 289(34): 23977-91, 2014 Aug 22.
Article
em En
| MEDLINE
| ID: mdl-25006251
ABSTRACT
We examined the magnesium dependence of five class II myosins, including fast skeletal muscle myosin, smooth muscle myosin, ß-cardiac myosin (CMIIB), Dictyostelium myosin II (DdMII), and nonmuscle myosin IIA, as well as myosin V. We found that the myosins examined are inhibited in a Mg(2+)-dependent manner (0.3-9.0 mm free Mg(2+)) in both ATPase and motility assays, under conditions in which the ionic strength was held constant. We found that the ADP release rate constant is reduced by Mg(2+) in myosin V, smooth muscle myosin, nonmuscle myosin IIA, CMIIB, and DdMII, although the ADP affinity is fairly insensitive to Mg(2+) in fast skeletal muscle myosin, CMIIB, and DdMII. Single tryptophan probes in the switch I (Trp-239) and switch II (Trp-501) region of DdMII demonstrate these conserved regions of the active site are sensitive to Mg(2+) coordination. Cardiac muscle fiber mechanic studies demonstrate cross-bridge attachment time is increased at higher Mg(2+) concentrations, demonstrating that the ADP release rate constant is slowed by Mg(2+) in the context of an activated muscle fiber. Direct measurements of phosphate release in myosin V demonstrate that Mg(2+) reduces actin affinity in the M·ADP·Pi state, although it does not change the rate of phosphate release. Therefore, the Mg(2+) inhibition of the actin-activated ATPase activity observed in class II myosins is likely the result of Mg(2+)-dependent alterations in actin binding. Overall, our results suggest that Mg(2+) reduces the ADP release rate constant and rate of attachment to actin in both high and low duty ratio myosins.
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Texto completo:
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Difosfato de Adenosina
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Actinas
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Miosinas
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Proteínas Motores Moleculares
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Magnésio
Limite:
Animals
Idioma:
En
Revista:
J Biol Chem
Ano de publicação:
2014
Tipo de documento:
Article