Unexpected effects of the alteration of structure and stability of myoglobin and hemoglobin in ammonium-based ionic liquids

Abstract

The nature of solvent-biomolecule interactions is generally weak and non-specific. The addition of ionic liquids (ILs), which have emerged as a new class of solvents, strengthen the stability of some proteins whereas the same ILs weaken the stability of some other proteins. Although ILs are commonly used for the stabilization of biomolecules, the bimolecular interactions of their stabilization-destabilization is still an active subject of considerable interest and studies on this topic have been limited. To reveal the impact of ILs on the stability of proteins, a series of protic ILs possessing a tetra-alkyl ammonium cation [R4N](+) with a hydroxide [OH](-) anion were synthesized. In this study, we report the structural stability of heme proteins such as myoglobin (Mb) and hemoglobin (Hb) in a series of ammonium-based ILs such as tetramethyl ammonium hydroxide [(CH3)4N](+)[OH](-) (TMAH), tetraethyl ammonium hydroxide [(C2H5)4N](+)[OH](-) (TEAH), tetrapropyl ammonium hydroxide [(C3H7)4N](+)[OH](-) (TPAH) and tetrabutyl ammonium hydroxide [(C4H9)4N](+)[OH](-) (TBAH) by fluorescence and circular dichroism (CD) spectroscopic studies. Our experimental results reveal that less viscous ILs carrying smaller alkyl chain such as TMAH are strong destabilizers of the heme proteins as compared to the ILs carrying bulkier alkyl chains which are more viscous ILs, such as TBAH. Therefore, our results demonstrate that the addition of these ILs to the heme proteins decreases their thermal stability allowing the protein to be in an unfolded state at lower temperatures. Further, we describe the molecular-structural interaction of the heme proteins with the ILs (molecule like a ligand) by the PatchDocking method.

Endeavour to simplify the frustrated concept of protein-ammonium family ionic liquid interactions

“…This leads to strong exclusion of less hydrated TEAP from the water molecules at the surface of protein in comparison to TMAP.So far literature considered anion effect on protein stability91 recently, we for the first time showed the effect of cation chain length on the structural stability of well known heme proteins Hb and Mb 92. We observed unfolding of heme protein induced by cations.…”

“…Conversely, Jha et al 92 bring into being that the thermal stability of the heme proteins Mb and Hb decreased with decrease in alkyl chain of the cation. Thus, the short alkyl chain cation containing IL TMAH was more denaturing than more hydrophobic long chain cation TBAH.…”

Spectroscopic insight into the interaction of bovine serum albumin with imidazolium‐based ionic liquids in aqueous solution

“…The decreased stability of BSA in the presence of ILs is attributed to the interactions of the hydrophobic group of IL with the hydrophobic region in the cavity of BSA. Interactions between functional groups of BSA and ions of IL and repulsive intermolecular interaction between functional groups of BSA cannot be ignored in the process of unfolding/ decreased T m values of BSA . These interactions loosen the native structure which leads to disruption of tertiary structure evidenced by the CD spectra discussed later in this section.…”

Effect of N‐Butyl‐N‐Methyl‐Morpholinium Bromide Ionic Liquid on the Conformation Stability of Human Serum Albumin

“…In the recent survey, it is found that the aqueous solution of ILs improves the stability, activity, and refolding ability of the protein by suppressing their irreversible aggregation . However, they also have some adverse effects on proteins i. e. destabilize the proteins/enzymes …”