X-ray Determination of Proteins and Viruses

9986266 Rossmann，M. X射线衍射和冷冻电子显微镜（cryo-EM）技术将用于分析各种病毒的组装和未包被中间体。 重点将放在dsDNA尾细菌phi 29和T4和ssDNA二十面体细菌Microviridae phiX 174和alpha 3。 其目的将是确定不仅是结构，但也组装中间体，包括DNA包装过程，是稳定的分子机制，然后在病毒形态发生的后续步骤触发。同样，将检查细胞感染期间病毒分解的结构中间体。 Cryo-EM将用于确定phi 29的主要组装中间体、成熟病毒和DNA排空病毒的低分辨率结构。X射线晶体学将用于确定形成成熟病毒所需的9种基因产物中的大多数（如果不是全部）的结构。这将允许将单个原子分辨率结构拟合到较低分辨率EM密度中。 X射线衍射被用于研究T4噬菌体基板的成分。 这个基板，其中长和短尾纤维都连接，经历了主要的构象变化，启动识别细胞表面受体，尾部收缩，并从病毒头部进入宿主细胞的DNA驱逐。 该噬菌体的整体结构及其基板的现有知识将通过冷冻EM扩展。 X射线衍射在早期已经用于研究成熟的phiX 174颗粒和空的原衣壳组装副产物。 然而，cryo-EM必须用于捕获不稳定的、真正的原衣壳组装前体。目前，这些研究正在用同源噬菌体α 3重复进行。 phiX 174和alpha 3的嵌合病毒可能稳定一些组装中间体，以允许晶体学研究。病毒结构研究的目标是了解病毒组装和拆卸对细胞感染的分子机制。 大分子结构的组装沿着有序的途径进行，并且通过蛋白质在加入新生组装体时在离散构象之间的转换来完成。 支架蛋白通常在组装过程中发挥催化作用，而不是像分子伴侣。X射线衍射和低温电子显微镜技术将用于分析组装和拆卸过程。

9986266Rossmann, M.X-ray diffraction and cryo-electron microscopy (cryo-EM) techniques will be used to analyze the assembly and uncoating intermediates of various viruses. The emphasis will be on the dsDNA tailed bacterial phages phi29 and T4 and the ssDNA icosahedral bacterial Microviridae phiX174 and alpha3. The objectives will be to determine not only the structures, but also the molecular mechanisms by which the assembly intermediates, including the DNA packaging process, are stabilized and then triggered for the subsequent steps in the viral morphogenesis. Similarly, the structural intermediates of viral disassembly during cellular infection will be examined. Cryo-EM will be used to determine the low resolution structures of the major assembly intermediates, the mature virus, and the DNA-emptied virus of phi29. X-ray crystallography will be used to determine the structures of most, if not all, of the 9 gene products that are required for the formation of the mature virus. This will allow the fitting of individual atomic resolution structures into the lower resolution EM densities. X-ray diffraction is being used to study components of the T4 phage baseplate. This baseplate, to which both the long and short tail fibers are attached, undergoes major conformational changes that initiate the recognition of cell surface receptors, the tail contraction, and the expulsion of the DNA from the viral head into the host cell. The available knowledge of the overall structure of this phage and its baseplate will be extended by cryo-EM. X-ray diffraction had been used earlier to study the mature phiX174 particle and an empty procapsid assembly byproduct. However, cryo-EM had to be used to capture the unstable, true procapsid assembly precursor. Currently, these studies are being repeated with the homologous phage alpha3. It is suspected that chimeric viruses of phiX174 and alpha3 may stabilize some of the assembly intermediates to permit crystallographic studies.The goal of the structural studies of viruses is to understand the molecular mechanisms of viral assembly and disassembly on cell infection. The assembly of a macromolecular structure proceeds along an ordered pathway and is accomplished by the switching of proteins between discrete conformations as they are added to the nascent assembly. Scaffolding proteins often play a catalytic role in the assembly process, rather like molecular chaperones. X-ray diffraction and cryo-electron microscopy techniques will be used to analyze the assembly and disassembly processes.