Coiled-coil nanomechanics and uncoiling and unfolding of the superhelix and alpha-helices of myosin.
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.
Root
Douglas D
DD
Department of Biological Sciences, University of North Texas, Denton, 76203-5220, USA.
Yadavalli
Vamsi K
VK
Forbes
Jeffrey G
JG
Wang
Kuan
K
D000595:Amino Acid Sequence; D000818:Animals; D001696:Biomechanical Phenomena; D006860:Hydrogen Bonding; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009218:Myosins / Q000737:chemistry* / Q000648:ultrastructure; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011817:Rabbits
D009218:Myosins