Testing the Suitability of Laxative for Protein Crystallization
Mentor 1
Nicholas Silvaggi
Start Date
28-4-2023 12:00 AM
Description
Angela M. McGinnis, Nicholas R. Silvaggi Polyethylene glycols (PEGs) are popular precipitants in protein crystallization experiments. While their precise mode of action is not known, they effectively alter the interactions between the protein and solvent, making it more favorable for protein molecules to associate with each other rather than the bulk solvent. PEG polymers are classified according to their average molecular weight. For example, PEG 8,000 has an average molecular weight of 8,000 Da. However, the range molecular weights (i.e. polymer lengths) present are not typically noted. There is a belief among macromolecular crystallographers that that the PEG 3,350 purchased from specialty suppliers like Hampton Research is purer—has a smaller range of molecular weights—and is therefore more desirable for crystallization. Indeed, Hampton Research sells a sparse matrix crystallization screen based on PEG 3350, the PEG/Ion Screen. A 500 g bottle of the so-called “monodisperse PEG 3,350” from Hampton Research currently sells for $189.00. Interestingly, PEG 3350 is not only useful for crystallizing proteins. It is also a first-rate laxative. The laxative formulation of PEG 3,350 is about one tenth the cost of the monodisperse PEG 3,350 and lists no other active or inactive ingredients on the label; it is pure PEG 3,350. As a laboratory that uses quite a bit of PEG 3,350 in our experiments, we were curious to know if this lower cost version of what appears to be the same chemical substance will be as effective as the monodisperse PEG 3,350 for protein crystallization.
Testing the Suitability of Laxative for Protein Crystallization
Angela M. McGinnis, Nicholas R. Silvaggi Polyethylene glycols (PEGs) are popular precipitants in protein crystallization experiments. While their precise mode of action is not known, they effectively alter the interactions between the protein and solvent, making it more favorable for protein molecules to associate with each other rather than the bulk solvent. PEG polymers are classified according to their average molecular weight. For example, PEG 8,000 has an average molecular weight of 8,000 Da. However, the range molecular weights (i.e. polymer lengths) present are not typically noted. There is a belief among macromolecular crystallographers that that the PEG 3,350 purchased from specialty suppliers like Hampton Research is purer—has a smaller range of molecular weights—and is therefore more desirable for crystallization. Indeed, Hampton Research sells a sparse matrix crystallization screen based on PEG 3350, the PEG/Ion Screen. A 500 g bottle of the so-called “monodisperse PEG 3,350” from Hampton Research currently sells for $189.00. Interestingly, PEG 3350 is not only useful for crystallizing proteins. It is also a first-rate laxative. The laxative formulation of PEG 3,350 is about one tenth the cost of the monodisperse PEG 3,350 and lists no other active or inactive ingredients on the label; it is pure PEG 3,350. As a laboratory that uses quite a bit of PEG 3,350 in our experiments, we were curious to know if this lower cost version of what appears to be the same chemical substance will be as effective as the monodisperse PEG 3,350 for protein crystallization.
