Methylamine Osmolytes in Protein Crystallography
PEG Induced Crystallization
Polyethylene glycol (PEG) is a well-known polymer that sees multiple uses, including in the growth of macromolecular crystals. PEG induced macromolecular crystallization is thought to function via an entropic mechanism called the depletion effect. Here the PEG molecules, which are somewhat smaller than the protein molecules, are excluded from the protein surface because of their finite size. If the protein molecules associate, then the volume of solution accessible to the PEG actually increases, which is entropically favorable. If enough PEG molecules are in the solution, then this can actually drive the protein molecules together into a crystal. Recent solution studies looking at a liquid-liquid phase transition have suggested that small molecular weight PEGs may instead produce an effective repulsion between protein molecules. We are investigating whether this is true for protein crystallization.