Evidence for structurally different attached states of myosin cross-bridges on actin during contraction of fish muscle

Abstract

Using data from fast time-resolved x-ray diffraction experiments on the synchrotrons at Daresbury and (Deutsches Elektronen Synchrotron [DESY]), it is shown that during contraction of fish muscle there are at least two distinct configurations of myosin cross-bridges on actin, that they appear to have different tension producing properties and that they probably differ in the axial tilt of the cross-bridges on actin. Evidence is presented for newly observed myosin-based layer lines in patterns from active fish muscle, together with intensity changes of the actin layer lines. On the equator, the 110 reflection changes much faster (time for 50% change t1/2 = 21 +/- 4 ms after activation) than the 100 reflection (t1/2 = 35 +/- 8 ms) and tension (t1/2 = 41 +/- 3 ms) during the rising phase of tetanic contractions. These and higher order reflections have been used to show the time course of mass attachment at actin during this rising phase. Mass arrival (t1/2 = 25 ms) precedes tension by approximately 15 ms. Analysis has been carried out to evaluate the effects of changes in sarcomere length during the tetanus. It is shown that any such effects are very small. Difference "equatorial" electron density maps between active muscle at a time when mass arrival at actin is just complete, but the tension is still rising, and at a later time well into the tension plateau, show that the structural difference between the lower and higher force states corresponds to mass movement consistent with axial swinging of heads from a nonstereospecific actin attached state (low force) to a more stereospecific (high force) state.

Cross-Bridge and Calcium Behavior in Ferret Papillary Muscle in Different Thyroid States.

“…Myosin heads which have moved to the vicinity of the thin filament take some time before they develop force in the strong binding state [20]. Structurally, this step may correspond to the "swinging" of myosin heads which is the origin of the sliding force between the actin and myosin filaments [21]. So far, X-ray evidence has not shown a correlation between the myosin ATPase and this delay time: chicken slow muscle has a longer delay than fast muscle [19] while heart muscle generally has a shorter delay than skeletal muscle.…”

3D Structure of Fish Muscle Myosin Filaments

“…Within the true 42.9-nm repeat the three crowns are spaced at slightly more or slightly less than the expected 14.3 nm (Huxley and Brown, 1967;Squire et al, 1982;Harford and Squire, 1986). Apart from its intrinsic interest as an example of how fibrous protein structures pack together (e.g., little is known about the disposition of the surface globular domains in intermediate filaments; Parry and Steinert, 1995), knowledge of where the myosin heads start in the force-producing myosin crossbridge cycle on actin in muscle is essential if the structural changes involved in the cycle are to be properly modeled and understood (Harford and Squire, 1992;Harford et al, 1998;Squire, 1998).…”

X-Ray Diffraction Studies of Striated Muscles

“…3(a)), with a time to 50% change of about 20 ms, it overshoots slightly, and then steadies to a high plateau value. We have shown this previously (Harford and Squire, 1992)…”

“…1), these parts can have different time-courses and they thus have the potential to illustrate the sequence of molecular events that takes place during muscle activation and force-generation (see Harford and Squire, 1992;Martin-Fernandez et al, 1994;Squire, 1998;2000;Squire et al, 2003c).…”

“…The muscles were treated as described by Harford and Squire (1992). Some preliminary results from this study are shown in Figure 3.…”