Kinetics and mass spectrometric measurements of myoglobin unfolding in aqueous ionic liquid solutions

Abstract

Recent studies have characterized the effects of aqueous ionic liquids on myoglobin unfolding for the broader purposes of understanding their effects on protein structures, stabilities, and ultimately biocompatibilities for future applications. Here, we investigated the effects of four different ionic liquids (ILs) on the thermal stability, unfolding kinetics, and tertiary shape of myoglobin. We compared results for four different ILs: 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIBF4); 1-butyl-3-methyl pyrrolidinium tetrafluoroborate (PyrrBF4); 1-ethyl-3-methyl imidazolium acetate (EMIAc); and tetramethylguanidinium acetate (TMGAc). Results showed that ILs accelerate myoglobin unfolding kinetics both through aqueous solution ionic strength effects and ionic liquid-specific effects. Arrhenius plots of observed rate constants reveal that some ILs lower the energy barrier to unfolding, possibly by destabilizing the native protein state. The magnitude of these ionic liquid effects correlates with their effects on protein thermodynamic stabilities. Hydrogen-deuterium exchange (HDX) experiments using ESI-MS showed that myoglobin exhibits a more open, and presumably less stable, tertiary shape in aqueous IL solutions. Overall, BMIBF4 and TMGAc exhibit the strongest effect on the myoglobin stability, unfolding rate, and tertiary structure while PyrrBF4 and EMIAc have weaker effects under our experimental conditions.

The protective action of osmolytes on the deleterious effects of gamma rays and atmospheric pressure plasma on protein conformational changes

“…Briefly, the 409 nm absorbance in the spectrum of native myoglobin in buffer was assumed to correspond to 100% folded protein, and the 409 nm absorbance in the spectrum of myoglobin with 9.0 M urea was assumed to correspond to 0% folded protein (similar to the previous work ref. 75 ). The folded fraction was computed as: In this method, A 409 is the absorbance, A u is the 409 nm absorbance of the unfolded protein, and A f is the absorbance of the folded protein.…”

Heme Dissociation from Myoglobin in the Presence of the Zwitterionic Detergent N,N-Dimethyl-N-Dodecylglycine Betaine: Effects of Ionic Liquids

“…In this work, the combination of several ILs (BMIBF 4 , BMICl, EMIAc) and control salts (LiBF 4 , NaCl) with the zwitterionic detergent Empigen BB (EBB) and the effects of these combinations on the oxygen storage protein myoglobin (Figure 1) was investigated. Myoglobin has proven to be a good model system for studying protein denaturation due to high solubility, uniformly α-helical structure, and visible absorbance signature arising from the heme cofactor [5,42,43]. Additionally, the conversion of myoglobin between apo- to holo- forms can be monitored by the same spectroscopic approaches.…”

“…The EBB is shown to induce minimal structural denaturation but does induce the loss of the heme group (holo- to apo-conversion). This resulted in a loss of absorptivity in the Soret band of the heme, loss of a CD signature around the same band, and a relief of iron/heme-based heavy-atom quenching of native Trp residues in the protein [42,43]. The results presented show that the EBB does not completely unfold the protein but does likely remove the heme group, and the effect of ILs on this process is negligible.…”

Surface active ionic liquid induced conformational transition in aqueous medium of hemoglobin

“…There are numerous studies where the effect of SAILs has been investigated on the aggregation behaviour of biopolymers, co-polymers and polyelectrolytes. [32][33][34][35][36][37] Singh et al have investigated the interactions of gelatin protein with room temperature ionic liquids and concluded the effect of hydrophobicity of ionic liquids on the conformation of gelatin. 32 Miller et al have studied the thermal stability and conformational changes in myoglobin in the presence of ionic liquids and reported that myoglobin undergoes destabilization and unfolding in the presence of ionic liquids.…”

“…32 Miller et al have studied the thermal stability and conformational changes in myoglobin in the presence of ionic liquids and reported that myoglobin undergoes destabilization and unfolding in the presence of ionic liquids. 33 Shu et al have demonstrated the folding-unfolding behaviour of bovine serum albumin in ionic liquids solutions and reported that probing of protein-ionic liquids interactions is method dependent. 34 Till now, the interactions of SAILs and blood plasma protein hemoglobin have been scarcely investigated.…”