Protein Crystallization by Forced Flow through Glass Capillaries: Enhanced Lysozyme Crystal Growth

The growth of protein crystals in quiescent mode depends on the supply of protein in a closed vessel, where crystals grow to a size limited by the mass of protein in solution in contact with the crystal. Here, we show that by inducing solution flow into a lower temperature environment, protein crystals grow in capillaries faster and larger than those obtained under quiescent conditions in sealed capillaries. The crystal size distribution is also more regular under capillary flow. In 27 h, lysozyme crystals grow up to 0.37 mm under flow conditions and 0.16 mm under quiescent conditions. A 75-fold concentration of crystal mass relative to a sealed batch crystallization was attained within an equivalent capillary space using this flow technique with a greater volume of protein solution. We have exploited this feature to develop a circulatory system to maximize the yield of crystals obtained by capillary flow. Recirculating the protein solution through each capillary for 40 h increases the crystal yield to 80% of total protein, close to that of a sealed capillary batch control crystallization. This method offers promise for growing large protein crystals for use in structure determinations and for the mass preparation of protein therapeutics.