Nearing the end of a crystallographers' nightmare?
Study of ionic liquids’ properties most suited for protein crystallization
Analysing protein crystals is a way to determine their structure and infer their function. However, forming crystals out of proteins is still a complex mix of empiricism and art. Now ionic liquids have entered into protein chemistry as helpers for their crystallization. Researchers at the Molecular Thermodynamics Lab and collaborators from REQUIMTE have systematically analysed a number of ionic liquids to determine which ones are most adequate for protein crystallization and why. The work is published in Crystal Engineering Communications, a Royal Society of Chemistry journal.
Ionic liquids are a class of compounds composed of two oppositly charged molecular species, the anion and the cation; they have a wide range of uses. The number of total possible combinations of ions is immense and it is possible to design a given ionic liquid that best suits a specific, desired purpose. The only catch, and it’s a big one, is that first one needs to know how the ionic liquid properties relate to that particular purpose, in this case protein crystallization. What researchers did in this study was to identify the variables and mechanisms behind the effect of twelve different ionic liquids on the crystallization of two positively charged proteins. They found, for example, that bulkier anions with a greatly dispersed distribution of negative charge were more suitable for the crystallization of the tested proteins.
While the tests were performed using two model proteins, researchers believe that this work may save a lot of future experimental work. Instead of testing ionic liquids at random to check whether protein crystals are formed, crystallographers may now simply select those predicted to be more adequate. The next step is to test the ability of those ionic liquids in the crystallization of difficult proteins.
Hofmeister effects of ionic liquids in protein crystallization: direct and water-mediated interactions.
Magdalena Kowacz , Abhik Mukhopadhyay , Ana Luísa Moreira Carvalho , José M.S.S. Esperança , Maria João Romão and Luis Paulo N. Rebelo