The CCP13 FibreFix program suite: semi-automated analysis of diffraction patterns from non-crystalline materials.

The extraction of useful information from recorded diffraction patterns from non-crystalline materials is non-trivial and is not a well defined operation. Unlike protein crystallography where one expects to see well behaved diffraction spots in predictable positions defined by standard space groups, the diffraction patterns from non-crystalline materials are very diverse. They can range from uniaxially oriented fibre patterns which are completely sampled as Bragg peaks, but rotationally averaged around the fibre axis, to fibre patterns that are completely unsampled, to either kind of pattern with considerable axial misalignment (disorientation), to liquid-like order and even to mixtures of these various structure types.

The myosin filament superlattice in the flight muscles of flies: A-band lattice optimisation for stretch-activation?

Low-angle X-ray diffraction patterns from relaxed fruitfly (Drosophila) flight muscle recorded on the BioCat beamline at the Argonne Advanced Photon Source (APS) show many features similar to such patterns from the "classic" insect flight muscle in Lethocerus, the giant water bug, but there is a characteristically different pattern of sampling of the myosin filament layer-lines, which indicates the presence of a superlattice of myosin filaments in the Drosophila A-band. We show from analysis of the structure factor for this lattice that the sampling pattern is exactly as expected if adjacent four-stranded myosin filaments, of repeat 116 nm, are axially shifted in the hexagonal A-band lattice by one-third of the 14.5 nm axial spacing between crowns of myosin heads.