-helices
are more or less aligned along the filament axis. Toshiro Oda, Kouji Makino, Ichiro Yamashita, Keiichi Namba & Yuichiro Maeda
International Institute for Advanced Research, Matsushita Electric Industrial Co., Ltd. 3-4 Hikaridai, Seika 619-02, Japan
The X-ray fiber diffraction method is potentially powerful in high resolution
structure analysis of fibrous macromolecular complexes with helical symmetry.
We have obtained good diffraction patterns from well-oriented F-actin sols.
A typical procedure we established to make well-oriented F-actin sols is
followings. F-actin filaments, whose lengths were controlled by adding
gelsolin, were spun down at 12,000 g for approximately 20 h. The resulting
soft pellet ( liquid crystalline protein concentration, 100 mg/ml ) was
drawn into a quartz capillary (diameter, 0.7mm). The soft pellet of F-actin
in the capillary was further concentrated by centrifugation at 2,000g for
1 day. A strong magnetic field (13.5 Tesla) was finally applied to the
sols for 10 to 15 days. The X-ray diffraction patterns from F-actin sols
were recorded. The best-oriented sol so far obtained using this preparing
methods showed the disorientation angle of approximately 2.6°. A prominent
feature that has not been observed has shown up in the pattern; layer lines
with substantial intensities at an axial spacing of about 5 Å. This
suggests that -helices
are more or less aligned along the filament axis.