Fibre diffraction studies of biological macromolecules

Two fundamental structures in molecular biology, DNA and the α-helix, were determined using X-ray fibre diffraction data, and yet fibre diffraction occupies an obscure niche in structural biology. Relatively few structures are appropriate for the technique, and it seldom supplies data of the quality common in protein crystallography; however, it has proven indispensable in some cases. Here we outline some aspects of helix diffraction mathematics, and then illustrate the application of fibre diffraction by three case studies: DNA, filamentous bacterial viruses, and bacterial pili. These examples are illustrative, not exhaustive, and reviews of other important structures such as plant viruses, polysaccharides and amyloids are also cited, as appropriate. Finally we describe in more detail the methods currently used to obtain and analyze fibre diffraction patterns of biological macromolecules, to give a technique-oriented tutorial which may be useful to researchers who find that they require fibre diffraction for their work.