Ca2+ Causes Release of Myosin Heads from the Thick Filament Surface on the Milliseconds Time Scale

ArticleinJournal of Molecular Biology 327(1):145-58 · April 2003with7 Reads
DOI: 10.1016/S0022-2836(03)00098-6 · Source: PubMed
Abstract
We have used electron microscopy to study the structural changes induced when myosin filaments are activated by Ca2+. Negative staining reveals that when Ca2+ binds to the heads of relaxed Ca2+ -regulated myosin filaments, the helically ordered myosin heads become disordered and project further from the filament surface. Cryo-electron microscopy of unstained, frozen-hydrated specimens supports this finding, and shows that disordering is reversible on removal of Ca2+. The structural change is thus a result of Ca2+ binding alone and not an artifact of staining. Comparison of the two techniques suggests that negative staining preserves the structure induced by Ca2+ -binding. We therefore used a time-resolved negative staining technique to determine the time scale of the structural change. Full disordering was observed within 30 ms of Ca2+ addition, and had started to occur within 10 ms, showing that the change occurs on the physiological time scale. Comparison with studies of single heavy meromyosin molecules suggests that an increased mobility of myosin heads induced by Ca2+ binding underlies the changes in filament structure that we observe. We conclude that the loosening of the array of myosin heads that occurs on activation is real and physiological; it may function to make activated myosin heads freer to contact actin filaments during muscle contraction.
    • "This subsequently initiates the sarcoplasmic reticulum to release Ca 2+ molecules and bind to calmodulin (Jones, Bampouras & Comfort, 2013). Thus, myosin heads drift away from filament surfaces, allowing an easier connection with actin filaments during the subsequent power exercise (Zhao & Craig, 2003). Consequently, CT, which optimises PAP, provides greater motor-unit availability in subsequent muscular contractions, enhancing force potential (Crewther, Kilduff, Cook, Middleton, Bunce and Yang (2011). "
    [Show abstract] [Hide abstract] ABSTRACT: The purpose of this study was to examine the effects of 4-week contrast and maximal strength training programmes on punch force in 20-30 year male amateur boxers. Twenty amateur boxers (mean age 24.5 ± 3.5 yr.) took part in the study and were randomly allocated into two groups. A contrast training group (n = 10) performed three sets of back squats interspersed with jump-squats and bench presses rotated with bench press throws. Exercises were alternated on a set-by-set basis and completed for three sets of three repetitions, twice weekly for four-weeks in place of two regular training sessions. A maximal strength training group (n = 10) performed back squats and bench presses for six sets of three repetitions, twice per week during the same time period. Punch force measurements analysed jab and rear-hand cross punches, utilising a Herman Digital Trainer. Additionally, muscular strength was assessed using 1-repetition maximum on 2 resistance exercises (back squat and bench press). All subjects were tested pre- and post-intervention. Two-way analysis of variance (ANOVA) with repeated measures and Bonferroni-adjusted post-hoc statistical analyses were adopted. It was found that the group x trials interaction was significant (p< 0.0005) for each punch type, with mean force values in the contrast training group (jab: 17 g, rear-hand cross: 19.7 g) increasing greater than the maximal strength training group (jab: 15.5 g, rear-hand cross: 17 g) at the study’s conclusion. Similarly, significant improvements in muscular strength variables were observed in both groups for back squat (CT: 27.5%, MST: 18.8%) and bench press (CT: 26.9%, MST: 15.1%) exercises. It was concluded that contrast training is superior to maximal strength training at enhancing straight punching force and increasing muscular strength in male amateur boxers.
    Full-text · Thesis · Dec 2016 · Journal of Structural Biology
    • "The results of investigation on the functionality of skeletal muscle myosin bio-nanorobot showed that the steps size was fairly uniform with an average size of 11 nm under conditions of low load [22]. Muscle contraction process is also regulated by Ca 2+ ions [23]. At low Ca 2+ levels, actin-myosin interaction is inhibited, and muscle is at rest. "
    [Show abstract] [Hide abstract] ABSTRACT: Kinesin and muscle myosin are considered as physical bio-nanoagents able to sense their cells through their sensors, make decision internally, and perform actions through their actuators. This paper has investigated and compared the flexible (reactive, pro-active, and interactive) autonomous behaviors of kinesin and muscle myosin bio-nanorobots. Using an automata algorithm, the agent-based deterministic finite automaton models of the internal decision making processes of the bio-nanorobots (as their reactive and pro-active capabilities) were converted to their respective computational regular languages (as their interactive capabilities). The resulted computational languages could represent the flexible autonomous behaviors of the bio-nanorobots. The proposed regular languages also reflected the degree of the autonomy and intelligence of internal decision-making processes of the bio-nanorobots in response to their environments. The comparison of flexible autonomous behaviors of kinesin and muscle myosin bio-nanorobots indicated that both bio-nanorobots employed regular languages to interact with their environments through two sensors and one actuator. Moreover, the results showed that kinesin bio-nanorobot used a more complex regular language to interact with its environment compared with muscle myosin bio-nanorobot. Therefore, our results have revealed that the flexible autonomous behavior of kinesin bio-nanorobot was more complicated than the flexible autonomous behavior of muscle myosin bio-nanorobot.
    Full-text · Article · Nov 2013
    • "A comparison of the backbone diameters between the negatively stained and frozen-hydrated tarantula thick filaments reveals that the fixative effect of uranyl acetate and the subsequent drying does not affect the backbone of the thick filament (Fig. 4, Supplementary movie 1). On the other hand, rapid negative staining (Zhao and Craig, 2003a ) could be used to alternatively assess which fraction of the collapse is produced by the negative stain drying since this technique easily allows to explore the structural changes on the negatively stained myosin heads helices after drying (Zhao and Craig, 2003b). A better understanding of the origin of this $3 nm collapse is very important as the free head movability revealed by the comparison of negative stain and cryo-EM results (Fig. 4) supports the proposal that the free heads of tarantula relaxed muscle can sway out and in (so called ''swaying'' heads) by Brownian motion (Brito et al., 2011 ), which has functional implications for thick filament activation and force potentiation (Brito et al., 2011). "
    [Show abstract] [Hide abstract] ABSTRACT: Electron microscopy (EM) studies of 2D crystals of smooth muscle myosin molecules have shown that in the inactive state the two heads of a myosin molecule interact asymmetrically forming a myosin interacting-heads motif. This suggested that inactivation of the two heads occurs by blocking of the actin-binding site of one (free head) and the ATP hydrolysis site of the other (blocked head). This motif has been found by EM of isolated negatively stained myosin molecules of unregulated (vertebrate skeletal and cardiac muscle) and regulated (invertebrate striated and vertebrate smooth muscle) myosins, and nonmuscle myosin. The same motif has also been found in 3D-reconstructions of frozen-hydrated (tarantula, Limulus, scallop) and negatively stained (scallop, vertebrate cardiac) isolated thick filaments. We are carrying out studies of isolated thick filaments from other species to assess how general this myosin interacting-heads motif is. Here, using EM, we have visualized isolated, negatively stained thick filaments from scorpion striated muscle. We modified the iterative helical real space reconstruction (IHRSR) method to include filament tilt, and band-pass filtered the aligned segments before averaging, achieving a 3.3nm resolution 3D-reconstruction. This reconstruction revealed the presence of the myosin interacting-heads motif (adding to evidence that is widely spread), together with 12 subfilaments in the filament backbone. This demonstrates that conventional negative staining and imaging can be used to detect the presence of the myosin interacting-heads motif in helically ordered thick filaments from different species and muscle types, thus avoiding the use of less accessible cryo-EM and low electron-dose procedures.
    Full-text · Article · Sep 2012
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