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Updated: Jan 8, 2026

Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultrafast Force-Clamp Spectroscopy
Published on: July 1, 2021
Myosin Modulator Aficamten Inhibits Force by Altering Myosin's Biochemical Activity Without Changing Thick Filament
Saffie Mohran1, Kristina B Kooiker1, Ateeqa Naim2
1Division of Cardiology, Medicine, University of Washington, Seattle Washington, USA; Center of Translational Muscle Research, University of Washington, Seattle, Washington, USA; Center for Cardiovascular Biology, University of Washington, Seattle, Washington, USA; Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle, Washington, USA.
Abstract:
We investigated the effects of aficamten on cardiac muscle structure, biochemical activity, and contractile function. Aficamten does not structurally sequester myosin heads along the thick filament. It inhibits ATPase activity by decreasing myosin ATPase cycling kinetics, with the emergence of a super slow biochemical nucleotide turnover. This results in decreased force and calcium sensitivity without altering cross-bridge cycling. Our myofibril mechanical assay showed inhibition of force with accelerated relaxation. In engineered heart tissues, while mavacamten and aficamten inhibit cardiac twitch forces, mavacamten reduces the activation kinetics while both accelerate relaxation.
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