Department of Chemistry and Biochemistry, Rowan University, Glassboro, NJ 08028, USA.
Department of Biological Sciences, Rowan University, Glassboro, NJ 08028, USA; Bantivoglio Honors College, Rowan University, Glassboro, NJ 08028, USA.
Int J Biol Macromol. 2021 Jun 1;180:355-364. doi: 10.1016/j.ijbiomac.2021.03.090. Epub 2021 Mar 17.
The thermal unfolding of the copper redox protein azurin was studied in the presence of four different amino acid-based ionic liquids (ILs), all of which have tetramethylguanidium as cation. The anionic amino acid includes two with alcohol side chains, serine and threonine, and two with carboxylic acids, aspartate and glutamate. Control experiments showed that amino acids alone do not significantly change protein stability and pH changes anticipated by the amino acid nature have only minor effects on the protein. With the ILs, the protein is destabilized and the melting temperature is decreased. The two ILs with alcohol side chains strongly destabilize the protein while the two ILs with acid side chains have weaker effects. Unfolding enthalpy (ΔH) and entropy (ΔS) values, derived from fits of the unfolding data, show that some ILs increase ΔHwhile others do not significantly change this value. All ILs, however, increase ΔS. MD simulations of both the folded and unfolded protein conformations in the presence of the ILs provide insight into the different IL-protein interactions and how they affect the ΔH values. The simulations also confirm that the ILs increase the unfolded state entropies which can explain the increased ΔS values.
铜氧化还原蛋白天青蛋白的热变性在四种不同的氨基酸基离子液体（ILs）存在下进行了研究，所有这些 ILs 都具有四甲基胍阳离子。阴离子氨基酸包括两个具有醇侧链的丝氨酸和苏氨酸，以及两个具有羧酸的天冬氨酸和谷氨酸。对照实验表明，氨基酸单独使用不会显著改变蛋白质稳定性，并且氨基酸性质所预期的 pH 值变化对蛋白质只有很小的影响。使用 ILs，蛋白质会失稳，熔点降低。具有醇侧链的两种 IL 强烈地使蛋白质失稳，而具有酸侧链的两种 IL 则具有较弱的影响。从展开数据的拟合中得出的展开焓（ΔH）和熵（ΔS）值表明，一些 ILs 增加了ΔH，而其他 ILs 则没有显著改变该值。然而，所有 ILs都增加了ΔS。在 ILs 存在下对折叠和展开蛋白质构象进行的 MD 模拟提供了对不同 IL-蛋白质相互作用的深入了解，以及它们如何影响ΔH 值。模拟还证实，ILs 增加了展开状态的熵，这可以解释增加的ΔS 值。
