Key result
The dynamics of bi-functionally labeled tropomyosin mutants decreased by three orders of magnitude when reconstituted into ghost muscle fibers, with the C-terminus being less mobile than other regions.
The study demonstrates that tropomyosin exhibits a gradient of mobility along its length in muscle fibers, which is decreased by troponin but unaffected by calcium or myosin S1, providing insights into the biophysics of muscle contraction regulation.
Supports biophysical models of tropomyosin mobility in fibers; leaves open translation to cardiac contractile disorders.
The dynamics of four regions of tropomyosin was assessed using saturation transfer electron paramagnetic resonance in the muscle fiber. In order to fully immobilize the spin probe on the surface of tropomyosin, a bi-functional spin label was attached to i,i+4 positions via cysteine mutagenesis. The dynamics of bi-functionally labeled tropomyosin mutants decreased by three orders of magnitude when reconstituted into "ghost muscle fibers". The rates of motion varied along the length of tropomyosin with the C-terminus position 268/272 being one order of magnitude slower then N-terminal domain or the center of the molecule. Introduction of troponin decreases the dynamics of all four sites in the muscle fiber, but there was no significant effect upon addition of calcium or myosin subfragment-1.
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Rayes et al. (2011) studied this question. Bi-functional spin label HO-1944 on tropomyosin mutants vs. Wild-type tropomyosin or isolated tropomyosin in solution was evaluated on Dynamics (effective correlation time) of tropomyosin. The dynamics of bi-functionally labeled tropomyosin mutants decreased by three orders of magnitude when reconstituted into ghost muscle fibers, with the C-terminus being less mobile than other regions.
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