Tomographic 3D reconstruction of quick-frozen, Ca2+-activated contracting insect flight muscle

Motor actions of myosin were directly visualized by electron tomography of insect flight muscle quick-frozen during contraction. In 3D images, active cross-bridges are usually single myosin heads, bound preferentially to actin target zones sited midway between troponins. Active attached bridges (app...

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Bibliographic Details
Published in:Cell 1999-11, Vol.99 (4), p.421-431
Main Authors: Taylor, K A, Schmitz, H, Reedy, M C, Goldman, Y E, Franzini-Armstrong, C, Sasaki, H, Tregear, R T, Poole, K, Lucaveche, C, Edwards, R J, Chen, L F, Winkler, H, Reedy, M K
Format: Article
Language:English
Subjects:
Actins - metabolism
Animals
Calcium
Flight, Animal
Freezing
Hemiptera - physiology
Image Processing, Computer-Assisted - methods
Microscopy, Electron - methods
Models, Biological
Muscle Contraction - physiology
Muscle Fibers, Skeletal - metabolism
Muscle Fibers, Skeletal - physiology
Muscle Fibers, Skeletal - ultrastructure
Myosin Light Chains - metabolism
Time Factors
Tomography - methods
Troponin - metabolism
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Summary:Motor actions of myosin were directly visualized by electron tomography of insect flight muscle quick-frozen during contraction. In 3D images, active cross-bridges are usually single myosin heads, bound preferentially to actin target zones sited midway between troponins. Active attached bridges (approximately 30% of all heads) depart markedly in axial and azimuthal angles from Rayment's rigor acto-S1 model, one-third requiring motor domain (MD) tilting on actin, and two-thirds keeping rigor contact with actin while the light chain domain (LCD) tilts axially from approximately 105 degrees to approximately 70 degrees. The results suggest the MD tilts and slews on actin from weak to strong binding, followed by swinging of the LCD through an approximately 35 degrees axial angle, giving an approximately 13 nm interaction distance and an approximately 4-6 nm working stroke.
ISSN:0092-8674
DOI:10.1016/s0092-8674(00)81528-7