title: Quantitative evaluation of myoglobin unfolding in the presence of guanidinium hydrochloride and ionic liquids in solution.
abstract: The use of ionic liquids in biochemical and biophysical applications has increased dramatically in recent years due to their interesting properties. We report results of a thermodynamic characterization of the chaotrope-induced denaturation of equine myoglobin in two different ionic liquid aqueous environments using a combined absorption/fluorescence spectroscopic approach. Denaturation by guanidinium hydrochloride was monitored by loss of heme absorptivity and limited unfolding structural information was obtained from Förster resonance energy transfer experiments. Results show that myoglobin unfolding is generally unchanged in the presence of ethylmethylimidazolium acetate (EMIAc) in aqueous solution up to 150 mM concentration but is facilitated by butylmethylimidazolium boron tetrafluoride (BMIBF4) in solution. The presence of 150 mM BMIBF4 alone does not induce unfolding but destabilizes the structure as observed by a decrease in threshold denaturant concentration for unfolding and an 80% decrease in the magnitude of ΔGunfolding from 44 kJ/mol in the absence of BMIBF4 to 8 kJ/mol in the presence of 150 mM BMIBF4. Thus, the BMIBF4 significantly destabilizes the myoglobin structure while the EMIAc does not, likely due to differences in anion interaction capabilities. This is confirmed with control studies using NaAc and LiBF4 solutions. EMIAc may be chosen as cosolvent additive with minimal effects on protein structure while BMIBF4 may be used as a supplement in protein folding experiments, potentially allowing access to proteins which have been traditionally difficult to denature as well as designing ionic liquids to match protein characteristics.
authors.affiliation: Department of Chemistry and Biochemistry and ‡School of Biomedical Sciences, Rowan University , 201 Mullica Hill Road, Glassboro, New Jersey 08028, United States.
authors.forename: Olivia C
authors.initials: OC
authors.lastname: Fiebig
authors.forename: Emily
authors.initials: E
authors.lastname: Mancini
authors.forename: Gregory
authors.initials: G
authors.lastname: Caputo
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Vaden
mesh_terms: D001881:Borates / Q000737:chemistry; D031541:Fluorescence Resonance Energy Transfer; D019791:Guanidine / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D009211:Myoglobin / Q000737:chemistry* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D058767:Protein Unfolding; D019346:Sodium Acetate / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D001881:Borates; D052578:Ionic Liquids; D009211:Myoglobin; D012996:Solutions; C440777:lithium tetrafluoroborate; D019346:Sodium Acetate; D019791:Guanidine