Regulatory proteins alter nucleotide binding to acto-myosin of sliding filaments in motility assays.
Biophys J
; 85(2): 1046-52, 2003 Aug.
Article
em En
| MEDLINE
| ID: mdl-12885651
ABSTRACT
The sliding speed of unregulated thin filaments in motility assays is only about half that of the unloaded shortening velocity of muscle fibers. The addition of regulatory proteins, troponin and tropomyosin, is known to increase the sliding speed of thin filaments in the in vitro motility assay. To learn if this effect is related to the rate of MgADP dissociation from the acto-S1 cross-bridge head, the effects of regulatory proteins on nucleotide binding and release in motility assays were measured in the presence and absence of regulatory proteins. The apparent affinity of acto-heavy meromyosin (acto-HMM) for MgATP was reduced by the presence of regulatory proteins. Similarly, the regulatory proteins increase the concentration of MgADP required to inhibit sliding. These results suggest that regulatory proteins either accelerate the rate of MgADP release from acto-HMM-MgADP or slow its binding to acto-HMM. The reduction of temperature also altered the relationship between thin filament sliding speed and the regulatory proteins. At lower temperatures, the regulatory proteins lost their ability to increase thin filament sliding speed above that of unregulated thin filaments. It is hypothesized that structural changes in the actin portion of the acto-myosin interface are induced by regulatory protein binding to actin.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Tropomiosina
/
Trifosfato de Adenosina
/
Actinas
/
Subfragmentos de Miosina
/
Proteínas Motores Moleculares
/
Movimento (Física)
Idioma:
En
Revista:
Biophys J
Ano de publicação:
2003
Tipo de documento:
Article
País de afiliação:
Estados Unidos