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          Institute: MPI für medizinische Forschung     Collection: Abteilung Biophysik     Display Documents

ID: 307534.0, MPI für medizinische Forschung / Abteilung Biophysik
A comparison of muscle thin filament models obtained from electron microscopy reconstructions and low−angle X−ray fibre diagrams from non−overlap muscle
Translation of Title:A comparison of muscle thin filament models obtained from electron microscopy reconstructions and low−angle X−ray fibre diagrams from non−overlap muscle
Authors:Poole, Katrina J. V.; Lorenz, Michael; Evans, Gwyndaf; Rosenbaum, Gerd; Pirani, Alnoor; Craig, Roger; Tobacman, Larry; Lehman, William; Holmes, Kenneth C.
Date of Publication (YYYY-MM-DD):2006-08-01
Title of Journal:Journal of Structural Biology
Journal Abbrev.:J. Struct. Biol.
Issue / Number:2
Start Page:273
End Page:284
Review Status:Peer-review
Audience:Experts Only
Intended Educational Use:No
Abstract / Description:The regulation of striated muscle contraction involves changes in the interactions of troponin and tropomyosin with actin thin filaments. In resting muscle, myosin−binding sites on actin are thought to be blocked by the coiled−coil protein tropomyosin. During muscle activation, Ca2+ binding to troponin alters the tropomyosin position on actin, resulting in cyclic actin−myosin interactions that accompany muscle contraction. Evidence for this steric regulation by troponin−tropomyosin comes from X−ray data [Haselgrove, J.C., 1972. X−ray evidence for a conformational change in the actin−containing filaments of verterbrate striated muscle. Cold Spring Habor Symp. Quant. Biol. 37, 341−352; Huxley, H.E., 1972. Structural changes in actin and myosin−containing filaments during contraction. Cold Spring Habor Symp. Quant. Biol. 37, 361−376; Parry, D.A., Squire, J.M., 1973. Structural role of tropomyosin in muscle regulation: analysis of the X−ray diffraction patterns from relaxed and contracting muscles. J. Mol. Biol. 75, 33−55] and electron microscope (EM) data [Spudich, J.A., Huxley, H.E., Finch, J., 1972. Regulation of skeletal muscle contraction. II. Structural studies of the interaction of the tropomyosin−troponin complex with actin. J. Mol. Biol. 72, 619−632; O'Brien, E.J., Gillis, J.M., Couch, J., 1975. Symmetry and molecular arrangement in paracrystals of reconstituted muscle thin filaments. J. Mol. Biol. 99, 461−475; Lehman, W., Craig, R., Vibert, P., 1994. Ca(2+)−induced tropomyosin movement in Limulus thin filaments revealed by three−dimensional reconstruction. Nature 368, 65−67] each with its own particular strengths and limitations. Here we bring together some of the latest information from EM analysis of single thin filaments from Pirani et al. [Pirani, A., Xu, C., Hatch, V., Craig, R., Tobacman, L.S., Lehman, W. (2005). Single particle analysis of relaxed and activated muscle thin filaments. J. Mol. Biol. 346, 761−772], with synchrotron X−ray data from non−overlapped muscle fibres to refine the models of the striated muscle thin filament. This was done by incorporating current atomic−resolution structures of actin, tropomyosin, troponin and myosin subfragment−1. Fitting these atomic coordinates to EM reconstructions, we present atomic models of the thin filament that are entirely consistent with a steric regulatory mechanism. Furthermore, fitting the atomic models against diffraction data from skinned muscle fibres, stretched to non−overlap to preclude crossbridge binding, produced very similar results, including a large Ca2+−induced shift in tropomyosin azimuthal location but little change in the actin structure or apparent alteration in troponin position.
Free Keywords:Tropomyosin; Actin; Thin filament structure; Striated muscle activation; Calcium activation; Steric blocking; Myosin crossbridge; Crossbridge binding
Last Change of the Resource (YYYY-MM-DD):--
External Publication Status:published
Document Type:Article
Communicated by:Wulf Kaiser
Affiliations:MPI für medizinische Forschung/Abteilung Biophysik
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