Three-dimensional image reconstruction of actin-tropomyosin complex and actin-tropomyosin-troponin T-troponin I complex

• Published in: Journal of molecular biology Vol. 93; no. 4; pp. 477,IN3,IN5,485 - 484,IN3,IN17,497
• Main Authors: Wakabayashi, T., Huxley, H.E., Amos, L.A., Klug, A.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 25.04.1975
• Subjects: Actins; Animals; Calcium - metabolism; Crystallization; Electrons; Electrophoresis, Polyacrylamide Gel; Mathematics; Microscopy, Electron; Models, Structural; Muscle Contraction; Muscle Proteins; Muscles - ultrastructure; Protein Conformation; Rabbits; Scattering, Radiation; Tropomyosin; Troponin
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/0022-2836(75)90241-7

The structure of the actin-tropomyosin complex, which represents on active form of the thin filaments of skeletal muscle and the actin-tropomyosin-troponin T-troponin I complex, which represents an inhibited form, have been studied by three-dimensional reconstruction from electron micrographs. A model of the three-dimensional structure of the actin-tropomyosin complex obtained by averaging the twelve “best” sets of data showed that the structure of the helix was polar and that the actin-tropomyosin contact was relatively loose. The detailed shape of the actin monomer and tropomyosin strands could be observed. A model of the three-dimensional structure of the actin-tropomyosin-troponin T-troponin I complex obtained by averaging the nine “best” sets of data showed that the contact between the actin and tropomyosin was very close in the inhibited filament, where the position of tropomyosin differed by approximately 10 Å from that in the active filament. The biological significance of the change in the extent of the actin-tropomyosin contact and of the movement of tropomyosin is discussed with reference to the mechanism of the regulation of muscle contraction by the tropomyosin-troponin-calcium system.