This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Previous workers have proposed high resolution models for the docking of the myosin heads on actin on the basis of combined crystallographic and electron microscopy data from isolated proteins (Mendelson and Morris, 1997 PNAS 94:8533;Holmes et al. 2003 Nature 425:423). Another group also claims that the first step in the force generation is associated with a rearrangement of the myosin-actin interface, followed by the lever arm tilt, and that it is temperature-dependent (Ferenczi et al. 2005 Structure 13:131). The goal of this work is to collect small angle X-ray scattering (SAXS) data from muscle that may be used to check in vivo the prediction of the models for the acto-myosin docking and whether there is a temperature-dependent rearrangement of the myosin-actin interface. For this purpose, the most sensitive reflection in the pattern is the 2.73nm meridional reflection arising from the regular repeat of the actin monomers along the actin filament, which changes its intensity upon myosin attachment to actin. Preliminary modelling has shown that the reflection intensity is little influenced by the lever arm tilt but it is highly sensitive to the relative axial position of actin and catalytic domain of myosin. 2D patterns will be taken from muscle at rest and during isometric contraction at different temperatures (4 to 17?C) up to 0.5 nm-1 in reciprocal space, in order to collect the actin-based 2.73nm meridional reflection and the 5.9nm and 5.1nm layer lines, also influenced by myosin attachment to actin.
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