Single-myosin crossbridge interactions with actin filaments regulated by troponin-tropomyosin. Proc Natl Acad Sci U S A 2005 Nov 22;102(47):16990-5
Date
11/17/2005Pubmed ID
16287977Pubmed Central ID
PMC1287988DOI
10.1073/pnas.0506326102Scopus ID
2-s2.0-28044433173 (requires institutional sign-in at Scopus site) 70 CitationsAbstract
Striated muscle contraction is governed by the thin filament regulatory proteins troponin and tropomyosin. Here, we investigate the molecular mechanisms by which troponin-tropomyosin inhibits myosin's interactions with the thin filament in the absence of calcium by using a laser trap. The displacement events for a single-myosin molecule interacting with a reconstituted thin filament were shorter (step size = 5 nm) and prolonged (69 ms) compared with actin alone (11 nm and 26 ms, respectively). However, these changes alone do not account for the degree of inhibition of thin filament movement observed in an ensemble assay. Our investigations of single- and multiple-myosin molecules with regulated thin filaments suggest the primary basis for this inhibition derives from an approximately 100-fold decrease in the probability of myosin attaching to actin. At higher myosin concentrations, short bursts of motility are observed in a laser trap consistent with the strong binding of a single-myosin crossbridge, resulting in cooperative binding of other cycling crossbridges. We confirmed this cooperativity in the in vitro motility assay by observing thin filament translocation in the absence of calcium but at low [ATP], consistent with rigor activation. We have developed a simple mechanistic model that reproduces and provides insight into both the observed single-myosin molecule and ensemble data in the absence of Ca(2+). These data support the hypothesis that thin filament inhibition in the absence of Ca(2+) is largely achieved by modulating the rate of attachment and/or transition from the weakly to strongly bound state.
Author List
Kad NM, Kim S, Warshaw DM, VanBuren P, Baker JEMESH terms used to index this publication - Major topics in bold
ActinsAdenosine Triphosphate
Animals
Calcium
Chickens
Computer Simulation
Magnesium
Models, Biological
Monte Carlo Method
Muscle Contraction
Muscle, Skeletal
Myosins
Tropomyosin
Troponin
