Protein Crystallization during Short-Duration Microgravity Exposure: Preliminary Results from the GEN-2 Capsule Aboard the MAPHEUS-17 Mission

Abstract Protein crystallization under microgravity conditions provides an opportunity to investigate crystal formation under altered mass-transport conditions, with potential implications for structural biology, pharmaceutical development, and bioengineering. However, the feasibility of initiating protein crystallization during short-duration microgravity exposure, particularly in the absence of pre-existing crystal seeds, remains insufficiently characterized. Here, we investigated the crystallization of purified hen egg-white proteins during a seven-minute microgravity phase aboard the MAPHEUS-17 sounding rocket using the GEN-2 capsule. Five sodium chloride (NaCl) concentrations were evaluated as precipitants, each tested with and without 0.1 M sodium acetate buffer. Protein and precipitant solutions were stored separately before flight and brought into contact during launch, enabling crystallization to initiate without pre-grown seed crystals. Following payload recovery, light microscopy screening revealed crystalline structures in six space-flown samples, with a preliminary count exceeding 100 structures approximately 5 µm in size. No crystalline structures were detected in the ground controls under the same screening conditions. The identity and structural properties of the observed crystals have yet to be confirmed, and further analyses are underway to assess their suitability for X-ray diffraction. These preliminary findings demonstrate the feasibility of initiating crystallization experiments during a brief sounding-rocket microgravity phase and provide a basis for systematic investigations of crystallization kinetics, experimental conditions, and crystal properties under short-duration microgravity.