Stafford W F, Mabuchi K, Takahashi K, Tao T
Muscle Research Group, Boston Biomedical Research Institute, Boston, Massachusetts 02114, USA.
J Biol Chem. 1995 May 5;270(18):10576-9. doi: 10.1074/jbc.270.18.10576.
Calponin is a thin filament-associated smooth muscle protein that has been suggested to play a role in the regulation of smooth muscle contraction. We have used circular dichroism spectroscopy, electron microscopy, and analytical ultracentrifugation to study the physical properties of recombinant chicken gizzard alpha-calponin. The alpha-helix content of alpha-calponin was estimated from its circular dichroism spectrum to be approximately 13%, alpha-Calponin melts with a single sharp transition at approximately 57 degrees C. Rotary shadowing electron micrographs of alpha-calponin reveal diverse shapes ranging from elongated rods to collapsed coils. The lengths of the rod-shaped structures are approximately 18 nm. Analytical ultracentrifugation studies found alpha-calponin to be homogeneous with a monomer molecular mass of 31.4 kDa, and a s20,w value of 2.34 S. These data could be used to model alpha-calponin as a prolate ellipsoid of revolution with an axial ratio of 6.16, a length of 16.2 nm, and a diameter of 2.6 nm. Taken together, our results indicate that calponin is a flexible, elongated molecule whose contour length is sufficient to span three actin subunits along the long pitch helix of an F-actin filament.
钙调蛋白是一种与细肌丝相关的平滑肌蛋白，有人认为它在平滑肌收缩调节中发挥作用。我们利用圆二色光谱、电子显微镜和分析超速离心法研究了重组鸡肌胃α-钙调蛋白的物理性质。根据其圆二色光谱估计，α-钙调蛋白的α-螺旋含量约为13%，α-钙调蛋白在约57℃时以单一尖锐转变发生熔解。α-钙调蛋白的旋转阴影电子显微照片显示出从细长杆状到塌陷盘绕等多种形状。杆状结构的长度约为18nm。分析超速离心研究发现，α-钙调蛋白是均一的，单体分子量为31.4kDa，s20,w值为2.34S。这些数据可用于将α-钙调蛋白模拟为长轴比为6.16、长度为16.2nm、直径为2.6nm的旋转扁长椭球体。综上所述，我们的结果表明，钙调蛋白是一种灵活的细长分子，其轮廓长度足以沿着F-肌动蛋白丝的长螺距螺旋跨越三个肌动蛋白亚基。
