MACROMOLECULAR STRUCTURE

大分子组装的结构与机理 和大分子复合物的研究，主要是通过高 计算机辅助分辨电子显微术 图像处理 在过去一年，我们的主要工作包括： 一直致力于分析（i）噬菌体的尾纤维 T7;和（ii）骨骼的冷冻水合横向薄切片 肌肉处于放松和僵硬状态。 (i)T7尾纤维代表了一种实验上易于处理的 病毒受体识别蛋白的实例。 我们有 电子组合分段相关平均 通过负染色和 通过冷冻干燥而不染色，预测基于 gp 17蛋白的已知序列（553个残基），以配制 这种纤维蛋白质的详细模型。 纤维是一种三聚体， 由三个域组成。 近端和远端半纤维 两个杆长约16 nm，以 大约90度，并通过 第三域。 特别感兴趣的是近端半纤维 其是α-螺旋的三链卷曲螺旋， 这类构造的几个可靠例子。 (ii)我们已经开发并应用了分析方法， 冰冻的含水的肌肉横切片。 这样的图像 联合收割机的优点是能很好地保存天然结构 （不同于传统的薄切片）和相位确定性（不同于 X射线纤维衍射）。 结果显示， 肌肉密度在放松和僵直状态下的分布 states.

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.