Thermodynamic destabilization of azurin by four different tetramethylguanidinium amino acid ionic liquids

Effects of Ionic Liquids on Laccase from Trametes versicolor

“…All other reagents were purchased from Thermo Fisher Scientific (Waltham, MA, USA), VWR (Radnor, PA, USA), or Sigma-Aldrich (St. Louis, MO, USA). TMG-ILs were synthesized as described previously and contained ~5% residual water as determined by FTIR spectroscopy [37]. Ionic liquid abbreviations used in the manuscript are: TMG-Ser (1,1,3,3-tetramethylguanidine glutamate), TMG-Thr (1,1,3,3tetramethylguanidine threonine), TMG-Asp (1,1,3,3-tetramethylguanidine aspartate), TMG-Glu (1,1,3,3-tetramethylguanidine glutamate), OMICl (1-octyl-3-methylimidazolium chloride,), HMICl (1-hexyl-3-methylimidazolium chloride,), EMICl (1-ethyl-3-methylimidazolium chloride), and BMICl (1-butyl-3-methylimidazolium chloride).…”

“…The ff14SB force field was used to represent the prepared laccase protein and the disulfide bonds within it. Ions characterizing the ILs were prepared using AMBER16 software and the GAFF2 force field and manually added to the laccase system; the force fields of TMG and Ser molecules were taken from our previous work [37]. Each IL system contained enough ions to constitute 0.05 M concentration.…”

“…The imidazolium ILs vary in the length of the alkyl group attached to the imidazole ring and have been shown to exert differing levels of protein destabilizing activity based on that alkyl chain length [22,23,41]. The amino acid ionic liquids are a newer class of ionic liquids and have been demonstrated to exert differential effects on protein stability based on amino acid R-group identity [37]. The amino acid ILs selected represent those with an alcohol in the side chain (Ser, Thr) and those with a carboxyl moiety in the side chain (Asp, Glu).…”

“…The Trp residue is an environmentally sensitive fluorophore which exhibits a dramatic shift in emission wavelength when moving between environments of low polarity and high polarity [42,43]. In the context of protein folding, Trp residues are often located at the interior of folded proteins where the side chain is shielded from the polar aqueous milieu, but as the protein denatures these Trp residues become more exposed to the aqueous environment, resulting in a shift in fluorescence emission spectra [37].…”

Sequence-specific destabilization of azurin by tetramethylguanidinium-dipeptide ionic liquids

“…Amino acid ILs (with the amino acid as anion) [ [26] , [27] , [28] , [29] ] offer many options for selective and tunable biocompatible ILs for a variety of biomedical/biotechnology applications. Similarly, the tetramethylguanidine (TMG) cation has been proposed as a suitable component for biomolecular interactions [ 30 , 31 ]. The IL TMG-acetate stabilizes H-bonding in DNA [ 32 ], TMG-lactate destabilizes the β-sheet structure in silk proteins [ 24 ], and our group has reported side-chain specific destabilization effects on the β-barrel protein mCherry by two different TMG-amino acid ILs [ 33 ].…”