F-actin retains a memory of angular order.
Modifications can be made to F-actin that do not interfere with the binding of myosin but inhibit force generation, suggesting that actin's internal dynamics are important for muscle contraction. Observations from electron microscopy and x-ray diffraction have shown that subunits in F-actin have a relatively fixed axial rise but a variable twist. One possible explanation for this is that the actin subunits randomly exist in different discrete states of "twist, " with a significant energy barrier separating these states. This would result in very slow torsional transitions. Paracrystals impose increased order on F-actin filaments by reducing the variability in twist. By looking at filaments that have recently been dissociated from paracrystals, we find that F-actin retains a "memory" of its previous environment that persists for many seconds. This would be consistent with slow torsional transitions between discrete states of twist.
Orlova
A
A
Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908-0733, USA.
Egelman
E H
EH
D000199:Actins / Q000737:chemistry* / Q000502:physiology / Q000648:ultrastructure; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D066298:In Vitro Techniques; D008854:Microscopy, Electron; D009038:Motion; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000737:chemistry / Q000502:physiology; D011817:Rabbits; D013816:Thermodynamics
D000199:Actins