MACROMOLECULAR STRUCTURE

大分子组装的结构和机理 和大分子络合物的研究，主要是通过高 分辨率电子显微镜与计算机的互补 图像处理。在过去的一年里，我们的主要努力 致力于分析(I)噬菌体尾部纤维 T7；和(Ii)冷冻水化的骨骼横切薄片 肌肉处于放松和僵硬的状态。 (I)T7尾部纤维代表了一种实验上易驯化的 病毒受体识别蛋白的例子。我们有 电子的联合分段关联平均 负染法制备的分子的显微照片 通过冷冻干燥而不沾染，并根据 已知的gp17蛋白序列(553个残基)，以制定 这种纤维蛋白的详细模型。这种纤维是三聚体 由三个域组成。近端和远端半纤维 两根棒子都大约16纳米长，以扭曲的角度连接在一起 大约90度，与病毒粒子通过 第三领域。特别令人感兴趣的是近端的半纤维 它是一个由阿尔法螺旋组成的三股螺旋线圈，是 很少有这种构象得到很好验证的例子。 (Ii)我们开发和应用了分析方法 冰冻水合的肌肉横向薄片。这样的图像 结合了保存完好的本土结构的优势 (不同于传统的薄片)和相位确定性(不同于 X射线纤维衍射)。结果显示， 肌肉在放松和僵直状态下的密度分布 各州。

The structures and mechanisms of assembly of macromolecules and marcromolecular complexes are studied, primarily by high resolution electron microscopy complemented with computer image processing. Over the past year, our major efforts have been devoted to analysis of (i) the tail-fibers of bacteriophage T7; and (ii) frozen-hydrated transverse thin sections of skeletal muscle in the relaxed and rigor states. (i) The T7 tail-fiber represents an experimentally tractable example of a viral receptor-recognition protein. We have combined piece-wise correlation averaging of electron micrographs of molecules prepared both by negative staining and by freeze-drying without staining, with predictions based on the known sequence of the gp17 protein (553 residues), to formulate a detailed model of this fibrous protein. The fiber is a trimer a consists of three domains. The proximal and distal half-fibers are both rods approximately 16nm long, joined at a kink-angle of approximately 90 degrees and are linked to the virion by the third domain. Of particular interest is the proximal half-fiber which is a triple-stranded coiled-coil of alpha-helices, one of the few well-authenticated examples of this conformation. (ii) We have developed and applied methods for the analysis of frozen-hydrated transverse thin sections of muscle. Such images combine the advantages of good preservation of native structure (unlike conventional thin sections) and phase determinacy (unlike X-ray fiber diffraction). The results reveal differences between the distributions of density in muscle in the relaxed and rigor states.