Ab Initio Phasing of Macromolecules

描述(申请人提供)：这项资助是为了从头开始解决阶段问题，这是结构生物学中一个经典的高风险/高影响挑战。大分子结构的测定将通过新的方法来改进，以识别非晶体对称性，指导方法和相延伸。第一个目标将是大分子结晶学中最常见、也往往是最具挑战性的情况：晶格中的分子具有和附加的非结晶学对称性。建议开发以下初步实施：-通过改进自旋函数来识别非晶体对称性的旋转分量；-从头开始识别分子的形状和位置的新方法；-有效地利用关于掩膜内电子密度的先验信息；-从头算通过共轭梯度法逐步提高到中等分辨率；-通过最先进的溶剂平坦化和NCS平均方法来延长相。这些方法将通过具有代表性的样本范围进行验证。预计所开发的框架将为普遍有效的后续应用奠定基础，从而使结构生物学家跳过费力和不确定的阶段来开发重原子衍生化晶体。在理解分子生物学方面，最高的预期影响是复杂分子组件的结构确定。

DESCRIPTION (provided by applicant): This grant is to solve ab initio the phase problem, a classic high risk/high impact challenge in structural biology. The macromolecular structure determination will be improved by novel approaches to identifying non-crystallographic symmetry, to direct methods an to phase extension. The first target will be the most frequent, and often the most challenging, cases in macromolecular crystallography: those of the molecules in the crystal lattice having and additional, non-crystallographic symmetry. The proposal is to develop the initial implementation of: - Identification of the rotational component of non-crystallographic symmetry by improving the self-rotation function; - A novel method to identify the molecule's shape and position ab initio; - Efficient use of the a priori information about the electron density inside the mask; - Ab initio phasing up to the intermediate resolution by conjugated gradient method; - Phase extension by state-of-the art solvent-flattening and NCS-averaging methods. These methods will be validated with a representative range of samples. It is expected that the developed framework will form a basis for the generally valid subsequent application that will led the structural biologists skip laborious and uncertain stage of developing heavy atom derivatized crystals. In terms of understanding the molecular biology, the highest expected impact is in structure determination of complex molecular assemblies.