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 3D-printed 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 in 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. Lysozyme single-crystal rotational crystallography at room temperature is shown, as well as microcrystal serial data collection under cryogenic conditions. 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 the membrane protein cytochrome c oxidase crystallized in lipidic cubic phase is presented.