Regulation of Lysozyme Crystallization Using Fluorescent Carbon Dots as Heterogeneous Nucleating Agents

Protein crystallization is critical for structural biology, and heterogeneous nucleation is an effective method for optimizing crystallization. Three fluorescent carbon dots (CDs) are used in this study as heterogeneous nucleating agents to improve crystallization. Their effects and intrinsic mechanism on lysozyme (Lys) crystallization are investigated. The results show that all three CDs exhibit excellent regulatory effects on Lys crystallization, with distinct differences among them. This may be closely related to the interactions between proteins and CDs as well as differences in the surface charge and functional groups of CDs. All three types of CDs can effectively improve the success rate of protein crystallization. Among which Green carbon dots (G-CDs) with high surface amino group content significantly promote crystal number and crystallization success rate by reducing nucleation energy barrier. Yellow carbon dots (Y-CDs) and Red carbon dots (R-CDs) have similar surface properties, leading to comparable crystallization promotion efficiency and enhancement of increasing the crystal size. This study firstly applies fluorescent CDs to the regulation of lysozyme crystallization, enabling the protein crystals to achieve fluorescence visualization. We also explored the intrinsic mechanism underlying the effects of CDs on protein crystallization. It will provide a new path for the optimization of protein crystallization and offer a theory basis for the interdisciplinary application of CDs in the biomedical field.