Biophysical Society Thematic Meeting | Canterbury 2023

Towards a More Perfect Union: Multi-Scale Models of Muscle and Their Experimental Validation

Monday Speaker Abstracts

MODELING THE TROPONIN CORE DOMAIN ON THIN FILAMENTS USING DATA FROM CRYOELECTRON MICROSCOPY AND FLUORESCENCE APPROACHES Michael J Rynkiewicz 1 ; Ivanka Sevrieva 2 ; Malcolm Irving 2 ; William Lehman 1 ; 1 Boston University Chobanian & Avedisian School of Medicine, Pharmacology, Physiology, & Biophysics, Boston, MA, USA 2 King's College London, Randall Centre for Cell & Molecular Biophysics, London, United Kingdom Our understanding of thin filament structure has been greatly enhanced by the publication of a number of models derived from cryo-electron microscopy studies (Yamada et al. (2020) and then later confirmed by Risi et al. (2021)). These studies elucidated atomic level details of the calcium-dependent activation of the thin filament leading to force development in cardiac muscle. However, while cryo-EM reconstruction is best suited to capture the high-resolution organization of static structures, troponin and tropomyosin are dynamic components of the thin filament and corresponding disorder is not always easily recorded and classified by the method. For example, the N-lobe of cardiac muscle troponin subunit C (TnC), which binds calcium and the troponin subunit I switch peptide during thin filament activation, has been shown to take up multiple distinct orientations in studies of polarized fluorescence of TnC labeled with bifunctional rhodamine (Sevrieva et al., 2014). Here, we generate small ensembles of structures to incorporate known sources of disorder as guided by information derived from multiple biophysical techniques. We use orientational data derived both from both polarized fluorescence and cryo-EM methodologies to guide molecular dynamics simulations to build a set of unique models that satisfy both sets of data. Analysis of these structures shows the details of how the dynamic nature of the N-lobe of TnC is important for its function in thin filament regulation.

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