The growth of high quality single protein crystals, yielding the highest X-ray resolution, remains a bottleneck in macromolecular crystallography. Convection-free conditions should lead to improved crystal quality, because in such a case growth is slow and the formation of defects and the incorporation of impurities minimized. Convection-free conditions have been achieved in the microgravity environment of space and in magnetic fields, but the impact on protein crystal growth has been limited due to the experimental difficulties with these methods.

Here we show that through a laboratory-based setup, an entirely convection-free crystallization environment is achieved, which enhances the purity and crystallinity of protein crystals [1]. This is accomplished by using an upside-down geometry, where crystals grow at the ‘ceiling’ of a growth cell completely filled with the crystallization solution. The ‘ceiling crystals’ experience the same diffusion-limited conditions as in space microgravity environments. The new method was tested on bovine insuline and two hen egg-white lysozyme polymorphs. In all cases, ceiling crystals diffracted X-rays to resolution limits beyond their current world records, even while solutions of moderate purity were used. The enhanced purification in the ceiling geometry is further demonstrated by comparing the crystal morphology and the fluorescence from impurities between normal batch-grown and ceiling crystals. Using phase-shifting interferometry, we show that indeed convection-free growth occurs.

[1] A. Adawy et al. (2013). Cryst. Growth & Design, 13, 775.

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