TY - JOUR
T1 - Ca2+-induced switching of troponin and tropomyosin on actin filaments as revealed by electron cryo-microscopy
AU - Narita, Akihiro
AU - Yasunaga, Takuo
AU - Ishikawa, Takashi
AU - Mayanagi, Kota
AU - Wakabayashi, Takeyuki
N1 - Funding Information:
We thank Dr Y. Matsuura, Dr K. Saeki, Mr K. Murakami, Mr T. Okada, and Mr S. Takeuchi for helpful discussions. We thank Dr Murray Stewart (MRC Laboratory of Molecular Biology, Cambridge) for reading the manuscript. This work was supported by a Grant-in-Aid for Specially Promoted Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan to T.W., a Grant for “Biodesign Research Program” from the Institute of Physical Chemical Research (RIKEN) to T.W., grant from the Mitsubishi Foundation and Human Frontier Science Program. We would like to dedicate this paper to Professor Setsuro Ebashi, who proposed calcium theory of muscle contraction and discovered troponin in 1965.
PY - 2001/4/27
Y1 - 2001/4/27
N2 - Muscle contraction is regulated by the intracellular Ca2+concentration. In vertebrate striated muscle, troponin and tropomyosin on actin filaments comprise a Ca2+-sensitive switch that controls contraction. Ca2+binds to troponin and triggers a series of changes in actin-containing filaments that lead to cyclic interactions with myosin that generate contraction. However, the precise location of troponin relative to actin and tropomyosin and how its structure changes with Ca2+have been not determined. To understand the regulatory mechanism, we visualized the location of troponin by determining the three-dimensional structure of thin filaments from electron cryo-micrographs without imposing helical symmetry to ∼35 Å resolution. With Ca2+the globular domain of troponin was gourd-shaped and was located over the inner domain of actin. Without Ca2+the main body of troponin was shifted by ∼30 Å towards the outer domain and bifurcated, with a horizontal branch (troponin arm) covering the N and C-terminal regions of actin. The C-terminal one-third of tropomyosin shifted towards the outer domain of actin by ∼35 Å supporting the steric blocking model, however it is surprising that the N-terminal half of tropomyosin shifted less than ∼12 Å. Therefore tropomyosin shifted differentially without Ca2+With Ca2+tropomyosin was located entirely over the inner domain thereby allowing greater access of myosin for force generation. The interpretation of three-dimensional maps was facilitated by determining the three-dimensional positions of fluorophores labelled on specific sites of troponin or tropomyosin by applying probabilistic distance geometry to data from fluorescence resonance energy transfer measurements.
AB - Muscle contraction is regulated by the intracellular Ca2+concentration. In vertebrate striated muscle, troponin and tropomyosin on actin filaments comprise a Ca2+-sensitive switch that controls contraction. Ca2+binds to troponin and triggers a series of changes in actin-containing filaments that lead to cyclic interactions with myosin that generate contraction. However, the precise location of troponin relative to actin and tropomyosin and how its structure changes with Ca2+have been not determined. To understand the regulatory mechanism, we visualized the location of troponin by determining the three-dimensional structure of thin filaments from electron cryo-micrographs without imposing helical symmetry to ∼35 Å resolution. With Ca2+the globular domain of troponin was gourd-shaped and was located over the inner domain of actin. Without Ca2+the main body of troponin was shifted by ∼30 Å towards the outer domain and bifurcated, with a horizontal branch (troponin arm) covering the N and C-terminal regions of actin. The C-terminal one-third of tropomyosin shifted towards the outer domain of actin by ∼35 Å supporting the steric blocking model, however it is surprising that the N-terminal half of tropomyosin shifted less than ∼12 Å. Therefore tropomyosin shifted differentially without Ca2+With Ca2+tropomyosin was located entirely over the inner domain thereby allowing greater access of myosin for force generation. The interpretation of three-dimensional maps was facilitated by determining the three-dimensional positions of fluorophores labelled on specific sites of troponin or tropomyosin by applying probabilistic distance geometry to data from fluorescence resonance energy transfer measurements.
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U2 - 10.1006/jmbi.2001.4598
DO - 10.1006/jmbi.2001.4598
M3 - Article
C2 - 11327765
AN - SCOPUS:0035957530
SN - 0022-2836
VL - 308
SP - 241
EP - 261
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
IS - 2
ER -