Whittaker M, Milligan R A
Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
J Mol Biol. 1997 Jun 20;269(4):548-57. doi: 10.1006/jmbi.1997.1058.
Brush border myosin I (BBMI) is a single-headed molecular motor. Its catalytic domain exhibits extensive sequence homology to the catalytic domain of myosin II, while its tail lacks the coiled-coil nature of myosin II. The BBMI tail domain contains at least three IQ motifs and binds calmodulin. Addition of calcium removes one of these calmodulin light chains, with effects on ATPase activity and motility in in vitro assays. Using the techniques of cryoelectron microscopy and helical image analysis we have calculated three-dimensional (3D) maps of BBMI-decorated actin filaments prepared in the presence and absence of calcium. The 3D maps describe a BBMI catalytic domain that is strikingly similar to the catalytic domain of myosin II subfragment 1 (S1), with the exception of a short amino-terminal region of the heavy chain, which is absent from BBMI. The tail domains of BBMI and S1 are highly divergent in structure, continuing on from their respective motor domains with very different geometries. Addition of calcium to BBMI, and the concomitant loss of a calmodulin light chain, results in an extensive reorganization of mass in the tail domain.
刷状缘肌球蛋白I（BBMI）是一种单头分子马达。其催化结构域与肌球蛋白II的催化结构域具有广泛的序列同源性，而其尾部缺乏肌球蛋白II的卷曲螺旋结构。BBMI尾部结构域至少包含三个IQ模体并结合钙调蛋白。添加钙离子会去除其中一条钙调蛋白轻链，这在体外实验中对ATP酶活性和运动性有影响。利用冷冻电子显微镜技术和螺旋图像分析，我们计算了在有钙和无钙条件下制备的由BBMI装饰的肌动蛋白丝的三维（3D）图谱。这些3D图谱描绘了一个与肌球蛋白II亚片段1（S1）的催化结构域惊人相似的BBMI催化结构域，除了重链的一个短氨基末端区域，BBMI中不存在该区域。BBMI和S1的尾部结构域在结构上高度不同，从各自的马达结构域继续延伸，具有非常不同的几何形状。向BBMI中添加钙离子以及随之而来的一条钙调蛋白轻链的丢失，导致尾部结构域的质量发生广泛重组。
