Solution small-angle X-ray scattering studies on myosin with a multiwire area detector

A point-focusing small-angle camera with a multiwire area detector is described along with its application in the study of the conformations of the myosin molecule. Myosin is one of the main contractile proteins, which, in smooth muscle and non-muscle cells, adopts a number of different conformations: for example an unfolded (6S) form which is capable of forming filaments and generating force and a `folded' (10S) form, which is most probably a storage form incapable of forming filaments. One of the aims of these solution scattering measurements is to confirm electron microscopic results under more `physiological' conditions and to explore the possibilities of doing kinetic measurements on the transition between the two states. Small-angle scattering from myosin molecules shows that the radius of gyration of cross section of the 10S form is greater than for the 6S form, presumably due to the folding up of the tail part of the molecule. Comparison of the scattering data with model structures shows very good fits for the 6S form of myosin when both S1 heads are assumed to be close together.