Mosaic spread analysis of Canadian advanced protein crystallization experiment on the Russian space station, Mir

Protein crystallization experiments were performed on the Russian space sta tion, Mir, using liquid-liquid interface diffusion. The technique was activ ated in orbit by the sliding together of two half-wells containing protein and precipitant fluids, respectively. Imperfections in protein crystals wer e analyzed from rocking curve measurements of the diffracted intensities us ing synchrotron radiation. Data were collected on microgravity and earth-gr own crystals, and 10 different protein pairs were compared. To avoid bias, a double-blind protocol was used throughout the data analysis. Rocking curv es for individual reflections were analyzed in terms of crystal domains, ea ch fitted by a three-dimensional Gaussian profile. The results of Gaussian analysis were consistent with domain segregation corresponding to spatially different regions of the protein crystal exhibiting distinct mosaic spread s. When crystals were grown in microgravity the domain mosaic spreads were consistent with five of 10 different proteins exhibiting fewer imperfection s, three other proteins showed no significant difference while a remaining two proteins displayed a greater number of apparent imperfections. Ground ( earth-grown) controls were also conducted on protein samples flown to asses s protein stability as a function of solution storage time prior to protein crystal growth (PCG) activation in microgravity. Protein samples were stor ed in ground controls at concentrations used to initiate crystallization, a nd aliquots were analyzed after a 30-day period by dynamic light scattering . Polydispersity estimates indicated that prolonged storage induced heterog eneity in all protein samples. Stable aggregates were present, and they wer e concentration independent, as shown by resistance to protein sample dilut ion. A PCG growth model is proposed that takes into account large scale agg regation or self-impurities present during crystal growth and predicts doma in segregation. Trapping or rejection of self-impurities using this model c an qualitatively explain differences in domain mosaic spreads observed as a function of gravitational environment. (C) 2001 Elsevier Science B.V. All rights reserved.