This project is concerned with determination of the three- dimensional molecular and crystal structures of biopolymers, primarily polysaccharides, using x-ray fiber diffraction analysis. Such polymers do not form extensive crystals that can be analyzed by traditional x-ray crystallography. However, they can often be prepared as fibers consisting of more-or-less parallel microcrystals. The structures of the polymers in such fibers can be determined by supplementing the x-ray diffraction data with stereochemical information, and optimizing model structures so that diffraction calculated from the model agrees with that measured, as well as possible. The goals of this project are: (1) To extend x- ray fiber diffraction technology by improving techniques for data collection, allowing use of data from more disordered polymer specimens, improving optimization of model structures and developing measures of accuracy; and (2) to determine the structures of a variety of polysaccharides of biological and industrial importance and so identify the intra- and inter- molecular interactions that are the molecular basis of their important properties. %%% The significance of this research is that: (1) It will allow x-ray diffraction analysis of biopolymers to be applied with more precision and more routinely, and to a wider range of biological polymers and assemblies. These developments will impact not only its applications to polysaccharides, but also to nucleic acids, helical viruses and membrane proteins that form disordered planar arrays. (2) The polysaccharide molecular structures and interactions determined will help us and others to understand why these molecules have the properties they do, and that such knowledge will both prompt and discipline further useful inquiries. Specific information to be expected includes the molecular basis of the useful viscosity properties of solutions of bacterial polysaccharides such as xanthan, acetan, wellan, and XM6, and the plant polysaccharide konjac mannan; and relationships between the molecular structures and biological functions of a number of polysaccharides that are important components of mammalian connective tissue and the exoskeleton of insects and crustaceans, that are antigens to some bacterial pathogens, and that are important in the process of nitrogen fixation.
