Coiled-Coil Nanomechanics and Uncoiling and Unfolding of the Superhelix and α-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...

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Bibliographic Details
Published inBiophysical journal Vol. 90; no. 8; pp. 2852 - 2866
Main Authors Root, Douglas D., Yadavalli, Vamsi K., Forbes, Jeffrey G., Wang, Kuan
Format Journal Article
LanguageEnglish
Published United States Elsevier Inc 15.04.2006
Biophysical Society
Subjects
Amino Acid Sequence
Animals
Biomechanical Phenomena
Hydrogen Bonding
Microscopy, Atomic Force
Models, Molecular
Molecular Sequence Data
Muscles and Contractility
Myosins - chemistry
Myosins - ultrastructure
Protein Folding
Protein Structure, Secondary
Rabbits
aa
FPLC
DTT
E
AFM
L
LMM
M
p
R
SHM
TCEP
S1
S2
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Summary: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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Douglas D. Root, Vamsi K. Yadavalli, and Jeffrey G. Forbes contributed equally to the work.
Address reprint requests to Dr. Kuan Wang, B50/Rm1140, LMB, NIAMS, NIH, Bethesda, MD 29892. Tel.: 301-496-4097; Fax: 301-402-8566; E-mail: wangk@exchange.nih.gov.
Abbreviations used: LMM, light meromyosin; aa, amino acids; AFM, atomic force microscopy; DTT, dithiothreitol; E, exponential phase; FPLC, kB, Boltzmann's constant; L, contour length; M, molecular mass; p, persistence length; P, plateau phase; R, rise phase; SHM, single-headed myosin; S1, myosin subfragment-1; S2, myosin long subfragment-2; TCEP, tri-(2-carboxyethyl)phosphine hydrochloride.
ISSN:0006-3495
1542-0086
DOI:10.1529/biophysj.105.071597