Crystallization of the collagen-like polypeptide (PPG)₁₀ aboard the International Space Station. 1. Video observation

Single chains of the collagen model polypeptide with sequence (Pro-Pro-Gly)₁₀, hereafter referred to as (PPG)₁₀, aggregate to form rod-shaped triple helices. Crystals of (PPG)₁₀ were grown in the Advanced Protein Crystallization Facility (APCF) both onboard the International Space Station (ISS) and on Earth. The experiments allow the direct comparison of four different crystallization environments for the first time: solution in microgravity (μg), agarose gel in μg, solution on earth, and gel on earth. Both on board and on ground, the crystal growth was monitored by a CCD video camera. The image analysis provided information on the spatial distribution of the crystals, their movement and their growth rate. The analysis of the distribution of crystals reveals that the crystallization process occurs as it does in batch conditions. Slow motions have been observed onboard the ISS. Different to Space-Shuttle experiment, the crystals onboard the ISS moved coherently and followed parallel trajectories. Growth rate and induction time are very similar both in gel and in solution, suggesting that the crystal growth rate is controlled by the kinetics at the interface under the used experimental conditions. These results provide the first data in the crystallogenesis of (PPG)₁₀, which is a representative member of non-globular, rod-like proteins.