Time-resolved X-ray diffraction of active bony fish muscle reveals a second, myosin-centered arrangement of crossbridges and a broad M3 meridional peak component consistent with strong-binding heads.
Time-resolved X-ray diffraction reveals distinct structural states of myosin crossbridges during active muscle contraction, advancing the understanding of molecular movements in muscle.
Some vertebrate muscles (e.g. those in bony fish) have a simple lattice A-band which is so well ordered that low-angle X-ray diffraction patterns are sampled in a simple way amenable to crystallographic techniques. Time-resolved X-ray diffraction through the contractile cycle should provide a movie of the molecular movements involved in muscle contraction. Generation of 'Muscle-The Movie' was suggested in the 1990s and since then efforts have been made to work out how to achieve it. Here we discuss how a movie can be generated, we discuss the problems and opportunities, and present some new observations. Low angle X-ray diffraction patterns from bony fish muscles show myosin layer lines that are well sampled on row-lines expected from the simple hexagonal A-band lattice. The 1st, 2nd and 3rd myosin layer lines at d-spacings of around 42.9 nm, 21.5 nm and 14.3 nm respectively, get weaker in patterns from active muscle, but there is a well-sampled intensity remnant along the layer lines. We show here that the pattern from the tetanus plateau is not a residual resting pattern from fibres that have not been fully activated, but is a different well-sampled pattern showing the presence of a second, myosin-centred, arrangement of crossbridges within the active crossbridge population. We also show that the meridional M3 peak from active muscle has two components of different radial widths consistent with (i) active myosin-centred (probably weak-binding) heads giving a narrow peak and (ii) heads on actin in strong states giving a broad peak.
Eakins et al. (Sat,) reported a other. Electrical stimulation of muscle vs. Resting muscle was evaluated on X-ray diffraction pattern changes (M3 meridional peak and ML1-ML3 layer lines). Time-resolved X-ray diffraction of active bony fish muscle reveals a second, myosin-centered arrangement of crossbridges and a broad M3 meridional peak component consistent with strong-binding heads.