Harmonic Force Spectroscopy Reveals a Force-Velocity Curve from a Single Human Beta Cardiac Myosin Motor

Jongmin Sung, Suman Nag, Christian L. Vestergaard, Kim Mortensen, Henrik Flyvbjerg, James Spudich

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    A muscle contracts rapidly under low load, but slowly under high load. This
    load-dependent muscle shortening has been described with a hyperbolic
    load-velocity curve. Its molecular mechanisms remain to be elucidated, however.
    During muscle contraction, myosins in thick filaments interact with actin in
    thin filaments in the sarcomere, cycling between a strongly bound state (force
    producing state) and a weakly bound state (relaxed state). Huxley and Simmons
    have previously proposed that the transition from the strong to the weak interaction can be modulated by an external load, i.e., the transition is slow under
    high load and fast under low load.
    We use a new, simple method we call "harmonic force spectroscopy" to
    extract a load-velocity relationship from a single human beta cardiac myosin
    II motor (S1). With a dual-beam optical trap, we hold an actin dumbbell over a
    single myosin molecule that is anchored to the microscope stage, which we
    oscillate sinusoidally in the direction of the dumbbell. Upon binding of the
    motor to the actin filament, it experiences an oscillatory load with a mean
    value that may be directed forward or backward, depending on where the binding took place. We find that the duration of the strongly bound state at saturating [ATP] is exponentially correlated with the mean load applied to the
    myosin during the bound state, which is explained by Arrhenius transition theory.
    With an independent stroke size measurement, we obtained an exponential
    load-velocity curve from a single human beta cardiac myosin S1. We also
    compare load-velocity curves for wild-type motors with load-velocity curves
    of mutant forms that cause hypertrophic or dilated-cardiomyopathy (HCM
    or DCM), in order to understand the effects of mutations on the contractile cycle
    at the single molecule level.
    Original languageEnglish
    JournalBiophysical Journal
    Issue number2
    Pages (from-to)453A
    Publication statusPublished - 2014
    Event58th Annual Meeting of the Biophysical-Society - San Fransisco, United States
    Duration: 15 Feb 201419 Feb 2014
    Conference number: 58


    Conference58th Annual Meeting of the Biophysical-Society
    Country/TerritoryUnited States
    CitySan Fransisco


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