A user-friendly goniometer-compatible fixed-target platform for macromolecular crystallography at synchrotrons

Fixed-target platforms provide convenient support for microcrystals during serial X-ray crystallography studies using synchrotron radiation. Here, we describe a simple, user-friendly 3Dprinted support where the crystals are sandwiched between two layers of thin X-ray transparent membrane resulting in very low scattering background. The platform is compatible with magnetic mounting onto the standard goniometer of macromolecular crystallography beamlines. Our design utilizes a 96-well frame that facilitates hanging-drop experiments directly on the membrane using conventional crystallization plates, thereby eliminating multiple pipetting and crystal handling steps. Crystals can be enclosed into a sandwich and packed into cassettes, preventing the risk of the sample drying out during room-temperature transportation to synchrotron sources. The versatility of the platform is demonstrated by five structures solved using different crystallization and data-collection strategies. Single crystal rotational-crystallography at both room- and cryogenic- temperatures using large crystals of lysozyme is shown. On chip microcrystallization is illustrated by use of a photosynthetic reaction center as an example. Finally, serial crystallography data collection at room-temperature from microcrystals of photosynthetic reaction center as well as cytochrome c oxidase crystallized in lipidic cubic phase is presented.