Photon Factory Activity Report 2004 #22 Part B (2005)
Biological Science

15A/2003G323

Modeling Analysis of Myosin-based Meridional Reflections from Skeletal
Muscles Stretched to the Non-overlap Length
Kanji OSHIMA, Yasunori TAKEZAWA, Yasunobu SUGIMOTO, and Katsuzo WAKABAYASHI*
Division of Biophysical Engineering, School of Engineering Science, Osaka University,Toyonaka, Osaka 560-8531, Japan
Introduction
The modeling analysis of the myosin-based meridionalreflections in the X-ray diffraction patterns of live frog
skeletal muscles at the full-overlap length was reported inthe previous report [1,2]. When muscles were stretchedto the non-overlap length of thin and thick filaments in asarcomere, the effect of the lateral filament arrays on theintensities of meridional reflections was more reduced
than that in the case of the full-overlap length due to thedisordering of the lattice structure. But it still remained insome meridional reflections. These intensities of thereflections were corrected as described previously [1,2].
Using the corrected data, we investigated to propose arelaxed model for the crossbridge structures of myosin
filaments in muscle with the non-overlap length and themodel was compared with that of myosin filaments inmuscle with the full-overlap length [2].
Experimental
Live frog sartorius muscles were used for X-ray studies.
X-ray diffraction experiments were performed at BL15A1.
The 2D-X-ray diffraction patterns from muscles stretchedto the non-overlap length were recorded with an image
plate at the specimen-to-detector distance of ca. 2.4 m.
Whether muscles were stretched to the non-overlap length
was made sure by measuring the diffraction periods fromthe sarcomere of stretched muscles with a laser. The Xray intensities were obtained by integration of the data in-4-1
the radial narrow range of 0 - 8.5x10 nm . The intensity
profile of a reflection was deconvoluted by Gaussianfunctions, yielding its integrated intensity and peak
position.
Results and Discussion
Compared the corrected intensity distribution of themyosin reflections from the non-overlapped muscle withthat of those reflections from the full-overlapped muscle,
they were seemed to be very similar. Using the corrected
intensities of the second to eleventh order myosin
meridional reflections from the non-overlapped muscle,
we carried out the modeling analysis as reported
previously [2]. In the model, the crown regions with aregular repeat of 14.3 nm (the regular regions) wereassumed to be located on both sides of the perturbed
region with a 43.2 nm period. The most probable model
was determined by searching the best fit of the calculated
intensities to those observed.
Figure 1 shows the distributions of the perturbed andregular regions of the myosin filaments in the nonoverlapped and full-overlapped muscles.
Figure 2
illustrates the configuration of two-headed myosincrossbridges along the thick filaments in the regular andperturbed regions.
Our simulation shows that thestructural models of crossbridges along the myosin
filaments in the non-overlapped and full-overlappedmuscles are fairly similar to each other. This suggeststhat the distribution and orientation of crossbridges along
the thick filaments doesn’t depend on the extent of theoverlap between myosin and actin filaments.
References[1] Oshima et al., PF Activity Rep #21 (2004)[2] Oshima et al., Fibre. Dif. Rev. 13 (2005)

Figure 1 The distribution of the arrays of myosincrossbridge along the thick filaments. A; the non-overlap
length, B; the full-overlap length.

Figure 2 The axial disposition of the two-headed myosincrossbridges along the thick filaments. A; the non-overlap
length, B; the full-overlap length.
*waka@bpe.es.osaka-u.ac.jp

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