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Fluorescence energy transfer studies of the tropomyosin movement in reconstituted skeletal muscle thin filaments
No full textMulti-site fluorescence energy transfer shows Ca2+-induced tropomyosin movement in reconstituted skeletal muscle thin filaments
No full textCa2+-induced movement of tropomyosin in skeletal muscle thin filaments observed by multi-site FRET
No full textTo obtain information on Ca2+-induced tropomyosin (Tm) movement in Ca2+-regulated muscle thin filaments, frequency-domain fluorescence energy transfer data were collected between 5-(2-iodoacetyl-amino-ethyl-amino)naphthalene-1-sulfonic acid at Cys-190 of Tm and phalloidin-tetramethylrhodamine B isothiocyanate bound to F-actin. Two models were used to fit the experimental data: an atomic coordinate (AC) model coupled with a search algorithm that varies the position and orientation of Tm on F-actin, and a double Gaussian distance distribution (DID) model. The AC model showed that little or no change in transfer efficiency is to be expected between different sites on F-actin and Tm if Ca2+ causes azimuthal movement of Tm of the magnitude suggested by structural data (C. Xu, R. Craig, L. Tobacman, R. Horowitz, and W. Lehman. 1999. Biophys. J. 77:985-992). However, Ca2+ produced a small but significant change in our phase/modulation versus frequency data, showing that changes in lifetime decay can be detected even when a change of the steady-state transfer efficiency is very small. A change in Tm azimuthal position of 17degrees on the actin filament obtained with the AC model indicates that solution data are in reasonable agreement with EM image reconstruction data. In addition, the data indicate that Tm also appears to rotate about its axis, resulting in a rolling motion over the F-actin surface. The DID model showed that the distance from one of the two chains of Tm to F-actin was mainly affected, further verifying that Ca2+ causes Tm to roll over the F-actin surface. The width of the distance distributions indicated that the position of Tm in absence and in presence of Ca2+ is well defined with appreciable local flexibility
Myosin-induced movement of alpha alpha, alpha beta, and beta beta smooth muscle tropomyosin on actin observed by multisite FRET
No full textThe interaction of the alphaalpha, betabeta, and alphabeta smooth muscle tropomyosin (Tm) isoforms with F-actin was systematically studied in the absence and in the presence of myosin subfragment 1 (S1) using multifrequency phase/modulation Forster resonance energy transfer (FRET). A Gaussian double distance distribution model was adopted to fit FRET data between a 5-(2-iodoacetyl-amino-ethyl-amino)naphthalene-1-sulfonic acid donor at either Cys-36 of the beta-chain or Cys-190 of the alpha-chain and a 4-dimethylaminophenylazophenyl 4'-maleimide acceptor at Cys-374 of F-actin. Experimental data were obtained for singly and doubly labeled alphabeta Tm (donor only at alpha, only at beta, or both) and for doubly labeled alphaalpha or betabeta Tm. Data for singly labeled alphabetaTm were combined in a global analysis with doubly labeled alphabetaTm. In all doubly labeled isoforms, upon S1 binding, one donor-acceptor "apparent" distance increased slightly by 0.5-2 Angstrom, whereas the other decreased by 6-9 Angstrom. These changes are consistent with a uniform "rolling" motion of Tm over the F-actin surface. The analysis indicates that Tm occupies relatively well-defined positions, with some flexibility, in both the predominantly closed (-S1) and open (+S1) thin-filament states. The results for the alphabetaTm heterodimer indicate that the local twofold symmetry of alphaalpha or betabeta Tm is effectively broken in alphabetaTm bound to F-actin, which implies a difference between the alpha- and beta-chains in terms of their interaction with F-actin
Myosin-induced movement and actin-binding specificity of smooth muscle alpha beta tropomyosin
No full textA global FRET study of the myosin-induced movement of alpha alpha, beta beta and alpha beta smooth muscle tropomyosin
No full textThe C-terminal region of tropomyosin (Tm) does not exhibit Ca2+-induced movement in reconstituted thin filaments
No full textCa2+ and myosin-induced changes of the proximity between troponin-1 and tropomyosin in the reconstituted thin filament. A global Lret study
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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