Pyridine-peg functionalized graphene nucleants for protein crystallization

Official URL: https://risc01.sabanciuniv.edu/record=b3074855_(Table of contents)

Structural characterization of proteins using X-Ray crystallography is crucial in protein-based applications. X-Ray crystallography requires protein crystals which can be grown using nucleants. Graphene and its derivatives are used as nucleants because they interact with proteins due to the hydrophobic and pi-pi stacking effect and increase protein concentration around their surface sites. Furthermore, polyethylene glycol(PEG) is another nucleating agent for protein crystallization. In this study, PEG-modified graphene nanostructures bearing positive charges are prepared as novel nucleants, and their nucleation ability is assessed. Pyridine-functionalized reduced graphene oxide (RGO-Pyr) is functionalized with three different PEG chains (PEG550, PEG2000, PEG5000), and octadecane (RGO-Pyr-OD). Six samples are tested as nucleants reduced graphene oxide (RGO), RGO-Pyr, RGO-Pyr-PEG550, RGO-Pyr-PEG2000 and RGO-Pyr-PEG5000. Protein crystallization is performed using the 4 hanging drop vapor diffusion method, and crystallization of lysozyme as model protein is monitored by a polarized light microscope. Protein crystals with good diffraction quality were obtained within 24 hours with all graphene nucleants except PEG2000, whereas control experiments with no graphene showed no crystals within the same period. The highest number of crystals was observed in droplets containing RGO due to the hydrophobic and pi-pi interactions between the RGO surface and lysozyme. RGO-Pyr produced a higher number of crystals with bigger sizes than PEGylated samples indicating a hydrogen bonding between the nitrogen atom of pyridine and lysozyme. The biggest crystals were obtained using RGO-Pyr-OD, attributed to the combined effect of pi and hydrophobic interactions arising from the positively charged pyridine and hydrophobic interactions between octadecane and lysozyme. The RGO-Pyr-OD shows promising potential as a novel nucleant for protein crystallization.