Additives for the crystallization of proteins and nucleic acids

Abstract

Numerous molecules have been described in literature as additives that were indispensable either for nucleation or growth of macromolecular crystals. In some cases, such additives were shown to improve the quality of the X-ray diffraction and to extend diffraction limits. We have investigated the effects of more than fifty compounds, belonging to several chemical families, on the crystallization of four model proteins (hen and turkey egg-white lysozymes, thaumatin, and aspartyl-tRNA synthetase from Thermus thermophilus). In addition, we have studied the crystallization of a ribonucleic acid from yeast, the transfer RNA specific for phenylalanine in the presence of synthetic polyamines. Crystals grown in the presence of the additives were optically evaluated and X-ray diffraction analyses were performed on selective crystals to compare their space group, cell parameters, and diffraction limit with those of controls. Whereas no changes in space group nor cell parameters were observed for the model proteins, significant improvements in diffraction limit were found when the transfer RNA was crystallized with certain synthetic polyamines.