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Optical Trapping (optical + trapping)
Selected AbstractsPhosphorylation of tropomyosin extends cooperative binding of myosin beyond a single regulatory unitCYTOSKELETON, Issue 1 2009Vijay S. Rao Abstract Tropomyosin (Tm) is one of the major phosphoproteins comprising the thin filament of muscle. However, the specific role of Tm phosphorylation in modulating the mechanics of actomyosin interaction has not been determined. Here we show that Tm phosphorylation is necessary for long-range cooperative activation of myosin binding. We used a novel optical trapping assay to measure the isometric stall force of an ensemble of myosin molecules moving actin filaments reconstituted with either natively phosphorylated or dephosphorylated Tm. The data show that the thin filament is cooperatively activated by myosin across regulatory units when Tm is phosphorylated. When Tm is dephosphorylated, this "long-range" cooperative activation is lost and the filament behaves identically to bare actin filaments. However, these effects are not due to dissociation of dephosphorylated Tm from the reconstituted thin filament. The data suggest that end-to-end interactions of adjacent Tm molecules are strengthened when Tm is phosphorylated, and that phosphorylation is thus essential for long range cooperative activation along the thin filament. Cell Motil. Cytoskeleton 2008. © 2008 Wiley-Liss, Inc. [source] Analysis of force generation during flagellar assembly through optical trapping of free-swimming Chlamydomonas reinhardtiiCYTOSKELETON, Issue 3 2005Rachel Patton McCord Abstract Many studies have used velocity measurements, waveform analyses, and theoretical flagella models to investigate the establishment, maintenance, and function of flagella of the biflagellate green algae Chlamydomonas reinhardtii. We report the first direct measurement of Chlamydomonas flagellar swimming force. Using an optical trap ("optical tweezers") we detect a 75% decrease in swimming force between wild type (CC124) cells and mutants lacking outer flagellar dynein arms (oda1). This difference is consistent with previous estimates and validates the force measurement approach. To examine mechanisms underlying flagella organization and function, we deflagellated cells and examined force generation during flagellar regeneration. As expected, fully regenerated flagella are functionally equivalent to flagella of untreated wild type cells. However, analysis of swimming force vs. flagella length and the increase in force over regeneration time reveals intriguing patterns where increases in force do not always correspond with increases in length. These investigations of flagellar force, therefore, contribute to the understanding of Chlamydomonas motility, describe phenomena surrounding flagella regeneration, and demonstrate the advantages of the optical trapping technique in studies of cell motility. Cell Motil. Cytoskeleton 61:137,144, 2005. © 2005 Wiley-Liss, Inc. [source] Cover Picture: J. Biophoton.JOURNAL OF BIOPHOTONICS, Issue 4 20104/2010 Glass substrate after femtosecond laser irradiation of six devices that will be obtained by six cuts along the transversal straight lines and a further orthogonal one. Chemical etching will create micro-channels where the more complex structures have been irradiated, while not affecting the inscribed optical waveguides. The devices will then be used for optical trapping and stretching of cells. (Picture: F. Bragheri et al., pp. 234,243 in this issue) [source] Simultaneous Raman micro,spectroscopy of optically trapped and stacked cellsJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2007P. R. T. Jess Abstract The combination of Raman spectroscopy and optical trapping holds great promise for single-cell studies and is an emergent theme in microfluidic environments. Here, the evolution of the Raman signal intensity with an axial increment of the mass of the substance of interest inside a specific Raman excitation volume is investigated. Whilst Raman spectroscopy may be applied to tissue samples, solutions and single cells, there are no easily available methods to rapidly acquire signals from small cell populations. We show a simple but powerful method to record the Raman intensity signal simultaneously from a small number of trapped cells or colloidal particles using the technique of optical stacking. The Raman spectra of stacks of red blood cells and yeast cells show that this method can be applied to biological systems. We demonstrate how we may reveal biochemical fingerprints that would otherwise require long integration times for each single cell or averaging over many sequentially acquired cell spectra. There is potential to apply this method to directly attain Raman spectra from sorted sub-populations of normal, abnormal and tumour cell lines. Copyright © 2007 John Wiley & Sons, Ltd. [source] Review fluorescence correlation spectroscopy for probing the kinetics and mechanisms of DNA hairpin formationBIOPOLYMERS, Issue 1 2008Alan Van Orden Abstract This article reviews the application of fluorescence correlation spectroscopy (FCS) and related techniques to the study of nucleic acid hairpin conformational fluctuations in free aqueous solutions. Complimentary results obtained using laser-induced temperature jump spectroscopy, single-molecule fluorescence spectroscopy, optical trapping, and biophysical theory are also discussed. The studies cited reveal that DNA and RNA hairpin folding occurs by way of a complicated reaction mechanism involving long- and short-lived reaction intermediates. Reactions occurring on the subnanoseconds to seconds time scale have been observed, pointing out the need for experimental techniques capable of probing a broad range of reaction times in the study of such complex, multistate reactions. © 2007 Wiley Periodicals, Inc. Biopolymers 89: 1,16, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | ||||||||||