Fibre diffraction studies of filamentous viruses

Filamentous viruses are long helical structures, and have a natural tendency to form fibres, but neither the viruses nor their constituent proteins can usually be crystallized. Even if crystals of the proteins can be grown, the molecular interactions rarely correspond to the biologically significant interactions in the filaments. Conventional macromolecular crystallography is therefore of little use in studying these structures. Fibre diffraction, however, has been an effective technique for visualizing the molecular structures of a number of filamentous viruses. Methods in fibre diffraction have been developed to the point where, in favourable cases, structures comparable in detail and reliability to crystallographic structures can be obtained. Structures at around 3 Angstrom resolution have been determined for four tobamoviruses (plant viruses) and two filamentous bacteriophages, and these structures, together with a number of structures at lower resolution, have illuminated many aspects of viral assembly, host interactions and technological applications.