Scattering from biopolymers with helical symmetry in solution

Small angle X-ray fibre diffraction on aligned elongated macromolecules has been a routine tool for the structure of materials that either can not be crystallized or in cases in which one wants to study the structure of the molecule as close as possible to those occurring in solution. One of the problems with this approach is that quite often it is not possible to obtain completely aligned samples but only samples in which there is an angular distribution around the main orientation axis. This has as a consequence that atlarger scattering angles the contributions from different layer lines start to overlap. A possible method to overcome this problem can be found in combining results from small angle solution scattering with small angle fibre diffraction from molecules aligned with their long axis parallel with respect to the X-ray beam. In the latter case one only observes the projection of the molecule on the basal plane. We show how this method can be applied to hydrated microtubules.