Jontes J D, Ostap E M, Pollard T D, Milligan R A
Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
J Cell Biol. 1998 Apr 6;141(1):155-62. doi: 10.1083/jcb.141.1.155.
The Acanthamoeba castellanii myosin-Is were the first unconventional myosins to be discovered, and the myosin-I class has since been found to be one of the more diverse and abundant classes of the myosin superfamily. We used two-dimensional (2D) crystallization on phospholipid monolayers and negative stain electron microscopy to calculate a projection map of a "classical" myosin-I, Acanthamoeba myosin-IB (MIB), at approximately 18 A resolution. Interpretation of the projection map suggests that the MIB molecules sit upright on the membrane. We also used cryoelectron microscopy and helical image analysis to determine the three-dimensional structure of actin filaments decorated with unphosphorylated (inactive) MIB. The catalytic domain is similar to that of other myosins, whereas the large carboxy-terminal tail domain differs greatly from brush border myosin-I (BBM-I), another member of the myosin-I class. These differences may be relevant to the distinct cellular functions of these two types of myosin-I. The catalytic domain of MIB also attaches to F-actin at a significantly different angle, approximately 10 degrees, than BBM-I. Finally, there is evidence that the tails of adjacent MIB molecules interact in both the 2D crystal and in the decorated actin filaments.
卡氏棘阿米巴肌球蛋白-I是最早被发现的非常规肌球蛋白，自那以后，肌球蛋白-I类被发现是肌球蛋白超家族中最多样化且含量丰富的类别之一。我们利用磷脂单层上的二维（2D）结晶和负染电子显微镜技术，以大约18埃的分辨率计算出一种“经典”肌球蛋白-I——卡氏棘阿米巴肌球蛋白-IB（MIB）的投影图。对投影图的解读表明，MIB分子垂直位于膜上。我们还利用冷冻电子显微镜和螺旋图像分析技术，确定了用未磷酸化（无活性）MIB修饰的肌动蛋白丝的三维结构。催化结构域与其他肌球蛋白的相似，而大的羧基末端尾部结构域与肌球蛋白-I类的另一个成员刷状缘肌球蛋白-I（BBM-I）有很大不同。这些差异可能与这两种肌球蛋白-I不同的细胞功能相关。MIB的催化结构域与F-肌动蛋白结合的角度也明显不同于BBM-I，约为10度。最后，有证据表明相邻MIB分子的尾部在二维晶体和修饰的肌动蛋白丝中都会相互作用。
