NSF Award
1518145
Macromolecular crystallographers visualize in extraordinary detail the large molecules needed for life, using X-ray diffraction analysis of crystals of these molecules to determine the locations of each atom in three dimensions, thereby describing the entire structure of the macromolecule. However, sometimes the crystals do not form in a way that permits accurate X-ray diffraction and analysis. The analytical tools to deal with this problem, when it happens, have not yet been developed, and the goal of this research project is to provide the methods and computer software needed to study the atomic structure of protein crystals of this nature. This method will computationally add another (4th) dimension to the structural analysis permitting "superstructures" of the molecule to be defined. This highly innovative project will open the field, permitting others to complete difficult but important multidimensional crystallography projects. This research will provide training for graduate and undergraduate students including members of groups underrepresented in science.<br/><br/>This project includes activities that will be beneficial to many areas of the biological sciences including macromolecular crystallography, cell biology and DNA repair. The project is focused on the structure determination of incommensurately modulated protein crystals. The unique diffraction patterns from modulated crystals contain "off-lattice" satellite reflections next to the main reflections. The intellectual merits of the proposed activity are multifold. The first incommensurately modulated protein crystal structures will be solved and advances will be made to the methodology of macromolecular crystallography. The main objective of this research is to develop new macromolecular X-ray crystallographic software for the refinement of incommensurately modulated crystals in superspace and to apply them to solve several crystal structures that currently cannot be solved. The methods employed include protein crystal growth, X-ray diffraction data collection and structure determination. Innovative approaches to protein crystallography and software development will be used. Activities will include extensive modification of crystallography software for the determination of macromolecular structures in superspace using modulation functions. Simulated data will be used as a test case. Then the algorithms will be applied to well characterized incommensurately modulated crystals of profilin:actin, UvsY recombination mediator crystals and then to many other unsolved modulated crystals. The resulting continuum of structures within each crystal will be analyzed within the framework of the current biological/biochemical literature.<br/><br/>This project is supported jointly by the Division of Molecular and Cellular Biosciences and the Division of Biological Infrastructure in the Directorate for Biological Sciences.
