Ionic Liquids as Protein Crystallization Additives.

Crissy L. Tarver,Marc L. Pusey,Qunying Yuan

doi:10.3390/cryst11101166

Abstract

Among its attributes, the mythical philosopher’s stone is supposedly capable of turning base metals to gold or silver. In an analogous fashion, we are finding that protein crystallization optimization using ionic liquids (ILs) often results in the conversion of base protein precipitate to crystals. Recombinant inorganic pyrophosphatases (8 of the 11 proteins) from pathogenic bacteria as well as several other proteins were tested for optimization by 23 ILs, plus a dH2O control, at IL concentrations of 0.1, 0.2, and 0.4 M. The ILs were used as additives, and all proteins were crystallized in the presence of at least one IL. For 9 of the 11 proteins, precipitation conditions were converted to crystals with at least one IL. The ILs could be ranked in order of effectiveness, and it was found that ~83% of the precipitation-derived crystallization conditions could be obtained with a suite of just eight ILs, with the top two ILs accounting for ~50% of the hits. Structural trends were found in the effectiveness of the ILs, with shorter-alkyl-chain ILs being more effective. The two top ILs, accounting for ~50% of the unique crystallization results, were choline dihydrogen phosphate and 1-butyl-3-methylimidazolium tetrafluoroborate. Curiously, however, a butyl group was present on the cation of four of the top eight ILs.

Highlights

Room temperature ionic liquids (RTILs), generally defined as salts that are liquid at ≤100 ◦ C, started attracting increased attention at the turn of the century
Nucleic acid sequences corresponding to the inorganic pyrophosphatases (IPPases) from Haemophilus influenzae (Hi), Klebsiella pneumonia (Kp), Acinitobacter baumannii (Ab), Campylobacter jejuni (Cj), Salmonella typhi (St), Francisella tularensis (Ft), Streptococcus pneumonia (Spn), and Streptococcus pyrogenes (Spy) were synthesized using previously described methods [21]
The crystalline nature of the outcomes is determined by the use of trace fluorescently labeled (TFL), high fluorescence intensity being associated with more dense packing of the fluorescent probes and higher packing density being a function of their crystalline state

Summary

Introduction

Room temperature ionic liquids (RTILs), generally defined as salts that are liquid at ≤100 ◦ C, started attracting increased attention at the turn of the century. They were known well before, it was not until this time that the advantages and utility of their unique properties became apparent. Subsequent crystallization experiments using four model proteins with three ILs, two based on the 1-butyl-3-methylimidazolium and one on the 1-butyl-1-methylpyrollidinium cation, each with a different anion, were carried out [2]. Ten ILs with cations based on the ethyl ammonium moiety were tested. This study was designed to test the effects of different anions. For all of the above IL-protein crystallization studies, the ILs were found to be best employed as additives, often effective in improving the size,

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Conclusion