Imaging modulated reflections from a semi-crystalline state of profilin:actin crystals

Modulated protein crystals remain terra incognita for most crystallographers. While small-molecule crystallographers have successfully wrestled with and conquered this type of structure determination, to date no modulated macromolecular structures have been reported. Profilin:β-actin in a modulated semi-crystalline state presents a challenge of sufficient biological significance to motivate the development of methods for the accurate collection of data on the complex diffraction pattern and, ultimately, the solution of its structure. In the present work, fine φ-sliced data collection was used to resolve the closely spaced satellite reflections from these polymorphic crystals. Image-processing methods were used to visualize these data for comparison with the original precession data. These preliminary data demonstrate the feasibility of using fine φ-slicing to collect accurately the intensities and positions of the main and satellite reflections from these modulated protein crystals.