Coiled-coil nanomechanics and uncoiling and unfolding of the superhelix and alpha-helices of myosin |
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| Authors: | Root Douglas D Yadavalli Vamsi K Forbes Jeffrey G Wang Kuan |
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| Affiliation: | Department of Biological Sciences, University of North Texas, Denton, 76203-5220, USA. |
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| Abstract: | The nanomechanical properties of the coiled-coils of myosin are fundamentally important in understanding muscle assembly and contraction. Force spectra of single molecules of double-headed myosin, single-headed myosin, and coiled-coil tail fragments were acquired with an atomic force microscope and displayed characteristic triphasic force-distance responses to stretch: a rise phase (R) and a plateau phase (P) and an exponential phase (E). The R and P phases arise mainly from the stretching of the coiled-coils, with the hinge region being the main contributor to the rise phase at low force. Only the E phase was analyzable by the worm-like chain model of polymer elasticity. Restrained molecular mechanics simulations on an existing x-ray structure of scallop S2 yielded force spectra with either two or three phases, depending on the mode of stretch. It revealed that coiled-coil chains separate completely near the end of the P phase and the stretching of the unfolded chains gives rise to the E phase. Extensive conformational searching yielded a P phase force near 40 pN that agreed well with the experimental value. We suggest that the flexible and elastic S2 region, particularly the hinge region, may undergo force-induced unfolding and extend reversibly during actomyosin powerstroke. |
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| Keywords: | LMM light meromyosin aa amino acids AFM atomic force microscopy DTT dithiothreitol E" target="_blank">E exponential phase FPLC kB Boltzmann’s constant L contour length M molecular mass p persistence length P" target="_blank">P plateau phase R" target="_blank">R rise phase SHM single-headed myosin S1 myosin subfragment-1 S2 myosin long subfragment-2 TCEP tri-(2-carboxyethyl)phosphine hydrochloride |
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