Construction of an atomic model of the skeletal muscle thin filament by FRET measurements

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Striated muscle thin filament is composed of actin, tropomyosin(Tm), and troponin(Tn). The fluorescence resonance energy(FRET) donor probe was labeled at the specific sites on tropomyosin or troponin, and the energy acceptor probes were labeled at the specific sites on actin. From these donor and acceptor pairs, FRET efficiencies were determined. Using the atomic coordinates of F-actin, Tm, and Tn, we searched all possible arrangements for Tn and Tm on F-actin to calculate FRET efficiency for each donor-acceptor pair in each arrangement. By minimizing the squared sum of deviations for the calculated FRET efficiencies from the observed efficiencies, we determined the location of Tm and Tn on F-actin.