The energetics of allosteric regulation of ADP release from myosin heads (original) (raw)
Related papers
Actomyosin-ADP States, Interhead Cooperativity, and the Force-Velocity Relation of Skeletal Muscle
Biophysical Journal, 2010
Despite intense efforts to elucidate the molecular mechanisms that determine the maximum shortening velocity and the shape of the force-velocity relationship in striated muscle, our understanding of these mechanisms remains incomplete. Here, this issue is addressed by means of a four-state cross-bridge model with significant explanatory power for both shortening and lengthening contractions. Exploration of the parameter space of the model suggests that an actomyosin-ADP state (AM*ADP) that is separated from the actual ADP release step by a strain-dependent isomerization is important for determining both the maximum shortening velocity and the shape of the force-velocity relationship. The model requires a velocity-dependent, cross-bridge attachment rate to account for certain experimental findings. Of interest, the velocity dependence for shortening contraction is similar to that for population of the AM*ADP state (with a velocity-independent attachment rate). This accords with the idea that attached myosin heads in the AM*ADP state position the partner heads for rapid attachment to the next site along actin, corresponding to the apparent increase in attachment rate in the model.
Journal of Biological Chemistry, 2009
Amrinone is a bipyridine compound with characteristic effects on the force-velocity relationship of fast skeletal muscle, including a reduction in the maximum shortening velocity and increased maximum isometric force. Here we performed experiments to elucidate the molecular mechanisms for these effects, with the additional aim to gain insight into the molecular mechanisms underlying the force-velocity relationship. In vitro motility assays established that amrinone reduces the sliding velocity of heavy meromyosin-propelled actin filaments by 30% at different ionic strengths of the assay solution. Stopped-flow studies of myofibrils, heavy meromyosin and myosin subfragment 1, showed that the effects on sliding speed were not because of a reduced rate of ATP-induced actomyosin dissociation because the rate of this process was increased by amrinone. Moreover, optical tweezers studies could not detect any amrinone-induced changes in the working stroke length. In contrast, the ADP affinity of acto-heavy meromyosin was increased about 2-fold by 1 mM amrinone. Similar effects were not observed for acto-subfragment 1. Together with the other findings, this suggests that the amrinone-induced reduction in sliding velocity is attributed to inhibition of a strain-dependent ADP release step. Modeling results show that such an effect may account for the amrinone-induced changes of the force-velocity relationship. The data emphasize the importance of the rate of a strain-dependent ADP release step in influencing the maximum sliding velocity in fast skeletal muscle. The data also lead us to discuss the possible importance of cooperative interactions between the two myosin heads in muscle contraction.
The Journal of Physiology, 2015
Muscle contraction is due to cyclical ATP-driven working strokes in the myosin motors while attached to the actin filament. Each working stroke is accompanied by the release of the hydrolysis products, orthophosphate and ADP. The rate of myosin-actin interactions increases with the increase in shortening velocity. r We used fast half-sarcomere mechanics on skinned muscle fibres to determine the relation between shortening velocity and the number and strain of myosin motors and the effect of orthophosphate concentration. r A model simulation of the myosin-actin reaction explains the results assuming that orthophosphate and then ADP are released with rates that increase as the motor progresses through the working stroke. The ADP release rate further increases by one order of magnitude with the rise of negative strain in the final motor conformation. r These results provide the molecular explanation of the relation between the rate of energy liberation and shortening velocity during muscle contraction.
Journal of Biological Chemistry, 2001
To understand mammalian skeletal myosin isoform diversity, pure myosin isoforms of the four major skeletal muscle myosin types (myosin heavy chains I, IIA, IIX, and IIB) were extracted from single rat muscle fibers. The extracted myosin (1-2 g/15-mm length) was sufficient to define the actomyosin dissociation reaction in flash photolysis using caged-ATP (Weiss, S., Chizhov, I., and Geeves, M. A. (2000) J. Muscle Res. Cell Motil. 21, 423-432). The ADP inhibition of the dissociation reaction was also studied to give the ADP affinity for actomyosin (K AD). The apparent second order rate constant of actomyosin dissociation gets faster (K 1 k ؉2 ؍ 0.17 ؊0.26 M ؊1 .s ؊1), whereas the affinity for ADP is weakened (250-930 M) in the isoform order I, IIA, IIX, IIB. Both sets of values correlate well with the measured maximum shortening velocity (V 0) of the parent fibers. If the value of K AD is controlled largely by the rate constant of ADP release (k ؊AD), then the estimated value of k ؊AD is sufficiently low to limit V 0. In contrast, [ATP]K 1 k ؉2 at a physiological concentration of 5 mM ATP would be 2.5-6 times faster than k ؊AD .
Biophysical Journal, 2004
The effects of myosin regulatory light chain (RLC) phosphorylation and strain on adenosine diphosphate (ADP) release from cross-bridges in phasic (rabbit bladder (Rbl)) and tonic (femoral artery (Rfa)) smooth muscle were determined by monitoring fluorescence transients of the novel ADP analog, 39-deac-eda-ADP (deac-edaADP). Fluorescence transients reporting release of 39-deac-eda-ADP were significantly faster in phasic (0.57 6 0.06 s ÿ1) than tonic (0.29 6 0.03 s ÿ1) smooth muscles. Thiophosphorylation of regulatory light chains increased and strain decreased the release rate ;twofold. The calculated (k ÿADP /k 1ADP) dissociation constant, K d of unstrained, unphosphorylated cross-bridges for ADP was 0.6 mM for rabbit bladder and 0.3 mM for femoral artery. The rates of ADP release from rigor bridges and reported values of P i release (corresponding to the steady-state adenosine triphosphatase (ATPase) rate of actomyosin (AM)) from cross-bridges during a maintained isometric contraction are similar, indicating that the ADP-release step or an isomerization preceding it may be limiting the adenosine triphosphatase rate. We conclude that the strain-and dephosphorylation-dependent high affinity for and slow ADP release from smooth muscle myosin prolongs the fraction of the duty cycle occupied by strongly bound actomyosin.ADP state(s) and contributes to the high economy of force.
Adenosine diphosphate and strain sensitivity in myosin motors
Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 2004
The release of adenosine diphosphate (ADP) from the actomyosin cross-bridge plays an important role in the adenosine-triphosphate-driven cross-bridge cycle. In fast contracting muscle fibres, the rate at which ADP is released from the cross-bridge correlates with the maximum shortening velocity of the muscle fibre, and in some models the rate of ADP release defines the maximum shortening velocity. In addition, it has long been thought that the rate of ADP release could be sensitive to the load on the cross-bridge and thereby provide a molecular explanation of the Fenn effect. However, direct evidence of a strain-sensitive ADP-release mechanism has been hard to come by for fast muscle myosins. The recently published evidence for a strain-sensing mechanism involving ADP release for slower muscle myosins, and in particular non-muscle myosins, is more compelling and can provide the mechanism of processivity for motors such as myosin V. It is therefore timely to examine the evidence for ...
Biophysical Journal, 1999
When smooth muscle myosin subfragment 1 (S1) is bound to actin filaments in vitro, the light chain domain tilts upon release of MgADP, producing a ϳ3.5-nm axial motion of the head-rod junction (Whittaker et al., 1995. Nature. 378:748-751). If this motion contributes significantly to the power stroke, rigor tension of smooth muscle should decrease substantially in response to cross-bridge binding of MgADP. To test this prediction, we monitored mechanical properties of permeabilized strips of chicken gizzard muscle in rigor and in the presence of MgADP. For comparison, we also tested psoas and soleus muscle fibers. Any residual bound ADP was minimized by incubation in Mg 2ϩ-free rigor solution containing 15 mM EDTA. The addition of 2 mM MgADP, while keeping ionic strength and free Mg 2ϩ concentration constant, resulted in a slight increase in rigor tension in both gizzard and soleus muscles, but a decrease in psoas muscle. In-phase stiffness monitored during small (Ͻ0.1%) 500-Hz sinusoidal length oscillations decreased in all three muscle types when MgADP was added. The changes in force and stiffness with the addition of MgADP were similar at ionic strengths from 50 to 200 mM and were reversible. The results with gizzard muscle were similar after thiophosphorylation of the regulatory light chain of myosin. These results suggest that the axial motion of smooth muscle S1 bound to actin, upon dissociation of MgADP, is not associated with force generation. The difference between the present mechanical data and previous structural studies of smooth S1 may be explained if geometrical constraints of the intact contractile filament array alter the motions of the myosin heads.
Biophysical Journal, 2009
A phosphorylated, single cysteine mutant of nucleoside diphosphate kinase, labeled with N-[2-(iodoacetamido)ethyl]-7-diethylaminocoumarin-3-carboxamide (P~NDPK-IDCC), was used as a fluorescence probe for time-resolved measurement of changes in [MgADP] during contraction of single permeabilized rabbit psoas fibers. The dephosphorylation of the phosphorylated protein by MgADP occurs within the lattice environment of permeabilized fibers with a second-order rate constant at 12 C of 10 5 M À1 s À1 . This dephosphorylation is accompanied by a change in coumarin fluorescence. We report the time course of P~NDPK-IDCC dephosphorylation during the period of active isometric force redevelopment after quick release of fiber strain at pCa 2þ of 4.5. After a rapid length decrease of 0.5% was applied to the fiber, the extra NDPK-IDCC produced during force recovery, above the value during the approximately steady state of isometric contraction, was 2.7 5 0.6 mM and 4.7 5 1.5 mM at 12 and 20 C, respectively. The rates of P~NDPK-IDCC dephosphorylation during force recovery were 28 and 50 s À1 at 12 and 20 C, respectively. The time courses of isometric force and P~NDPK-IDCC dephosphorylation were simulated using a seven-state reaction scheme. Relative isometric force was modeled by changes in the occupancy of strongly bound A.M.ADP.P i and A.M.ADP states. A strain-sensitive A.M.ADP isomerization step was rate-limiting (3-6 s À1 ) in the cross-bridge turnover during isometric contraction. At 12 C, the A.M.ADP.P i and the pre-and postisomerization A.M.ADP states comprised 56%, 38%, and 7% of the isometric force-bearing AM states, respectively. At 20 C, the force-bearing A.M.ADP.P i state was a lower proportion of the total force-bearing states (37%), whereas the proportion of postisomerization A.M.ADP states was higher (19%). The simulations suggested that release of cross-bridge strain caused rapid depopulation of the preisomerization A.M.ADP state and transient accumulation of MgADP in the postisomerization A.M.ADP state. Hence, the strain-sensitive isomerization of A.M.ADP seems to explain the rate of change of P~NDPK-IDCC dephosphorylation during force recovery. The temperature-dependent isometric distribution of myosin states is consistent with the previous observation of a small decrease in amplitude of the P i transient during force recovery at 20 C and the current observation of an increase in amplitude of the ADP-sensitive NDPK-IDCC transient.
Small segmental rearrangements in the myosin head can explain force generation in muscle
Biophysical Journal, 1996
Poisson-Boltzmann calculations of the distribution of electrostatic potentials around an actin filament in physiological-strength solutions show that negative isopotential surfaces protrude into the solvent. Each protrusion follows the actin two-start helix and is located on the sites implicated in the formation of the actomyosin complex. Molecular dynamic calculations on the Si portion of the myosin molecule indicate that in the presence of ATP the crystallographically invisible loops (comprising residues 624-649 and 564-579) remain on the surface, whereas in the absence of ATP they can move toward the actin-binding sites and experience electrostatic forces that range from 1 to 10 pN. The molecular dynamics calculations also suggest that during the ATP cycle there exist at least three states of electrostatic interactions between the loops and actin. Every time a new interaction is formed, the strain in the myosin head increases and the energy of the complex decreases by 2kT to 5kT. This can explain muscular contraction in terms of a Huxley-Simmons-type mechanism, while requiring only rearrangements of small mobile Si segments rather than the large shape changes in the myosin molecule postulated by the conventional tilting head model.