Crystals from Light:  Photochemically Induced Nucleation of Hen Egg-White Lysozyme

In a preliminary study on the light-induced nucleation of lysozyme (Okutsu T.; Furuta, K.; Terao T.; Hiratsuka H.; Yamano A.; Ferté N.; Veesler S. Cryst. Growth Des. 2005, 5, 1393−1398.), we proposed a nucleation mechanism. In this paper, we demonstrate that the irradiation of a metastable supersaturated lysozyme solution by a light produced by a continuous 150 W Xe lamp induces nucleation and that the mechanism is photochemically induced by a one-photon process. The irradiation of lysozyme molecules produces residual tryptophan radicals, which enhance the attractive interactions between molecules in solution, as shown by dynamic light scattering measurements, and increase the nucleation rate of lysozyme. When the intermediate is excited by visible light, the intermediate is converted into a permanently damaged species, and light-induced nucleation is inhibited, as shown by scavenger experiments (irradiation with two colors of excitation). These results suggest a new method for controlling nucleation and growth from metastable solutions that could be use in structural genomics and the pharmaceutical industry, for instance.