title: Structural changes of the regulatory proteins bound to the thin filaments in skeletal muscle contraction by X-ray fiber diffraction.
abstract: In order to clarify the structural changes related to the regulation mechanism in skeletal muscle contraction, the intensity changes of thin filament-based reflections were investigated by X-ray fiber diffraction. The time course and extent of intensity changes of the first to third order troponin (TN)-associated meridional reflections with a basic repeat of 38.4nm were different for each of these reflections. The intensity of the first and second thin filament layer lines changed in a reciprocal manner both during initial activation and during the force generation process. The axial spacings of the TN-meridional reflections decreased by approximately 0.1% upon activation relative to the relaxing state and increased by approximately 0.24% in the force generation state, in line with that of the 2.7-nm reflection. Ca(2+)-binding to TN triggered the shortening and a change in the helical symmetry of the thin filaments. Modeling of the structural changes using the intensities of the thin filament-based reflections suggested that the conformation of the globular core domain of TN altered upon activation, undergoing additional conformational changes at the tension plateau. The tail domain of TN moved together with tropomyosin during contraction. The results indicate that the structural changes of regulatory proteins bound to the actin filaments occur in two steps, the first in response to the Ca(2+)-binding and the second induced by actomyosin interaction.
authors: Division of Biophysical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
authors: Yasunobu
authors: Y
authors: Sugimoto
authors: Yasunori
authors: Y
authors: Takezawa
authors: Tatsuhito
authors: T
authors: Matsuo
authors: Yutaka
authors: Y
authors: Ueno
authors: Shiho
authors: S
authors: Minakata
authors: Hidehiro
authors: H
authors: Tanaka
authors: Katsuzo
authors: K
authors: Wakabayashi
mesh_terms: D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology* / Q000648:ultrastructure*; D011485:Protein Binding; D011487:Protein Conformation; D011892:Rana catesbeiana; D012518:Sarcomeres / Q000502:physiology / Q000648:ultrastructure; D014335:Tropomyosin / Q000502:physiology* / Q000648:ultrastructure*; D014336:Troponin / Q000502:physiology* / Q000648:ultrastructure*; D014961:X-Ray Diffraction
chemical_list: D014335:Tropomyosin; D014336:Troponin