Study of the Influence of a Precipitant Cation on the Formation of Oligomers in Crystallization Solutions of Lysozyme Protein

The influence of the precipitant cation type in a series of chlorides (NaCl, KCl, LiCl, NiCl2, CuCl2, CoCl2) on the structure of lysozyme solutions has been investigated by small-angle X-ray scattering (SAXS) under the conditions favorable for tetragonal crystal growth. The influence of the precipitant concentration on the volume fraction of the oligomers (dimers, octamers) formed before the protein crystallization has been studied. Along with monomers, significant amount of dimers (3.5-13.1%) and octamers (1.7-3.6%) is found in the lysozyme solutions when adding a precipitant. The volume fractions of all oligomers increase with an increase in the precipitant concentration and with a decrease in temperature. In the series of monovalent and divalent ions, the octamer volume fraction increases as K+ - Na+ - Li+ and Cu2+ - Ni2+ - Co2+, respectively.