Ab Initio Phasing of Macromolecules

描述（由申请人提供）：该资助旨在从头开始解决相位问题，这是结构生物学中典型的高风险/高影响挑战。通过识别非晶体对称性、直接方法和相扩展的新方法，将改进大分子结构的确定。第一个目标将是大分子晶体学中最常见的，通常也是最具挑战性的情况：晶格中的分子具有额外的非晶体对称。该方案是开发初步实现：-通过改进自旋转函数来识别非晶体对称的旋转分量；-一种从头开始识别分子形状和位置的新方法；-有效利用掩膜内电子密度的先验信息；-通过共轭梯度法从头算相位到中间分辨率；-通过最先进的溶剂平坦化和ncs平均方法进行相扩展。这些方法将在具有代表性的样本范围内进行验证。期望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开发重原子衍生化晶体的艰苦和不确定阶段。在理解分子生物学方面，最大的预期影响是复杂分子组装的结构确定。

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.