Single myosin molecule mechanics: piconewton forces and nanometre steps.

Department of Biochemistry, Beckman Center, Stanford University School of Medicine, California 94305.
Nature (Impact Factor: 42.35). 04/1994; 368(6467):113-9. DOI: 10.1038/368113a0
Source: PubMed

ABSTRACT A new in vitro assay using a feedback enhanced laser trap system allows direct measurement of force and displacement that results from the interaction of a single myosin molecule with a single suspended actin filament. Discrete stepwise movements averaging 11 nm were seen under conditions of low load, and single force transients averaging 3-4 pN were measured under isometric conditions. The magnitudes of the single forces and displacements are consistent with predictions of the conventional swinging-crossbridge model of muscle contraction.

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    • "Optical tweezers have been used to probe the cytoskeleton, study cell motility and have enabled the targeted delivery of nanoparticles into a specified region of the interior of an individual living cell (so-called optical injection) [5]. Optical tweezers were used to resolve the step-like motions of motor proteins such as kinesin [6] and myosin [7] and for demonstrating the ability of such motors to advance for hundreds of steps [8]. However, the broader development of optical-tweezer-based techniques and related advances into the smaller research budgets and day-to-day applications are hindered by their cost that is largely dictated by use of expensive and cumbersome vibronic lasers in typical setups. "
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    ABSTRACT: Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M2 values in double-digits. We propose a method of ‘interference’ superfocusing of high-M2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with high-precision direct laser writing. Using axicons with apex angle 1400 and rounded tip area as small as ~10 μm diameter, we demonstrate 2-4 μm diameter focused laser ‘needle’ beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M2=18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of ~11 μm that could be achieved if focused by an ‘ideal’ lens of unity numerical aperture. The same technique using a 1600 axicon allowed us to demonstrate few-μm-wide laser ‘needle’ beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations
    Proceedings of SPIE - The International Society for Optical Engineering 03/2015; 9343:93430Q. DOI:10.1117/12.2078957 · 0.20 Impact Factor
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    • "The two parameters  r and stiff,2 k are not independently identifiable from the analyzed data. Estimated values of  r range from 4 to 20 nm [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46]. Here we fix XB stroke size at 10 nm, as there is some consensus regarding this value [40] [41] [42] [43] [44] [45] [46]. "
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    ABSTRACT: Despite extensive study over the past six decades the coupling of chemical reaction and mechanical processes in muscle dynamics is not well understood. We lack a theoretical description of how chemical processes (metabolite binding, ATP hydrolysis) influence and are influenced by mechanical processes (deformation and force generation). To address this need, a mathematical model of the muscle cross-bridge (XB) cycle based on Huxley’s sliding filament theory is developed that explicitly accounts for the chemical transformation events and the influence of strain on state transitions. The model is identified based on elastic and viscous moduli data from mouse and rat myocardial strips over a range of perturbation frequencies, and MgATP and inorganic phosphate (Pi) concentrations. Simulations of the identified model reproduce the observed effects of MgATP and MgADP on the rate of force development. Furthermore, simulations reveal that the rate of force re-development measured in slack-restretch experiments is not directly proportional to the rate of XB cycling. For these experiments, the model predicts that the observed increase in the rate of force generation with increased Pi concentration is due to inhibition of cycle turnover by Pi. Finally, the model captures the observed phenomena of force yielding suggesting that it is a result of rapid detachment of stretched attached myosin heads.
    Journal of Molecular and Cellular Cardiology 02/2015; DOI:10.1016/j.yjmcc.2015.02.006 · 5.22 Impact Factor
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    • "These techniques, in effect, convert a laser intensity into a relative position so intensity fluctuations directly translate to spatial measurement errors. RMS intensity fluctuations of one per cent, for instance, can result in a spatial uncertainty of 10 s of nanometers, which may confound measurements on a range of phenomena [6] (e.g., in biological physics, the procession of the molecular motor Myosin I along actin moves in discrete steps of approximately 10 nm [7]). When discussing the level of stability necessary for an optical tweezing experiment, one should first consider the corner frequency f c of a typical optical trap [8]. "
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    ABSTRACT: Laboratories ranging the scientific disciplines employ feedback control to regulate variables within their experiments, from the flow of liquids within a microfluidic device to the temperature within a cell incubator. We have built an inexpensive, yet fast and rapidly deployed, feedback control system that is straightforward and flexible to implement from a commercially available Arduino Due microcontroller. This is in comparison with the complex, time-consuming and often expensive electronics that are commonly implemented. As an example of its utility, we apply our feedback controller to the task of stabilizing the main trapping laser of an optical tweezers. The feedback controller, which is inexpensive yet fast and rapidly deployed, was implemented from hacking an open source Arduino Due microcontroller. Our microcontroller based feedback system can stabilize the laser intensity to a few tenths of a per cent at 200 kHz, which is an order of magnitude better than the laserʼs base specifications, illustrating the utility of these devices.
    European Journal of Physics 07/2014; 35(5):055009. DOI:10.1088/0143-0807/35/5/055009 · 0.62 Impact Factor


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