Synergistic Effect of Graphene Oxide and Different Valence of Cations on Promoting Catalase Crystallization

Abstract

This study tests the effect of using the combination of graphene oxide (GO) with different valence cations as a heterogeneous nucleant on promoting catalase crystallization. By using GO and three types of salts with different valences, NaCl, MgCl2, and YCl3, the addition of GO with all three salts resulted in an increase in the percentage of crystal drops and a decrease in induction time. The experimental results further verified that there is a synergistic effect of GO and cations as the percentage of crystal drops was higher when GO with cations was added compared to control experiments where only GO or cations presented. It was also observed that the improvement in crystallization became more significant when cations with higher valence were utilized. It is believed that the enhancement in crystallization was due to the synergistic effect arising from the cation-π and electrostatic interactions between GO sheets and cations. These interactions subsequently contributed to the positively charged salt, which adsorbed and connected both negatively charged catalase molecules and the GO surfaces, increasing the local protein concentration and leading to crystallization. In addition, we compared LaCl3 and CeCl3 with YCl3 to verify the effect of the same valence salt on catalase crystallization and found that the higher the charge density, the more pronounced the promotion effect. This study provides a new protein crystallization methodology by exploiting GO with cations as heterogeneous nucleant to promote catalase crystallization and brings about a new model for investigating protein crystallization mechanisms.