A model of myosin crossbridge structure consistent with the low-angle x-ray diffraction pattern of vertebrate muscle

Low-angle X-ray diffraction patterns have been taken of relaxed frog sartorius muscles stretched to destroy the lattice sampling in the pattern and the observed layer line pattern has been interpreted with model-building studies. The modelling calculations indicate that each crossbridge cannot be represented by a single cylindrical shape, but that the two S-1 heads of the crossbridge are tilted in opposite directions along the filament while twisted the same way round it so that the crossbridge lies wrapped round the filament backbone. The radial position derived for the crossbridge depends on how many strands the filament is assumed to have. If the filament is 2, 3 or 4 stranded then the centre of mass of the crossbridge lies at about 9.5, 12.5, or 15.5 nm respectively from the filament axis.