Abstract
The effect of neutral salts on protein conformation was first analyzed by Hofmeister in 1888, however, even today this phenomenon is not completely understood. To clarify this effect, we studied changes in the secondary structure of two proteins: human serum albumin with predominantly α-helical structure and porcine pancreas β-trypsin with the typical β-structural arrangement in aqueous solutions of neutral salts (KSCN, KCl, (NH4)2SO4). The changes in the secondary structure were studied at 23 °C and 80 °C by using the second derivative deconvolution method of the IR spectra. Our results demonstrated that the ability of the salts to stabilize/destabilize these two proteins correlates with the Hofmeister series of ions. At the same time, some exceptions were also observed. The destabilization of the native structures of both α-helical albumin and β-structural trypsin upon interaction with neutral salts leads to the formation of intermolecular β-sheets typical for amyloid fibrils or amorphous aggregates. Thus, our quantitative FTIR-spectroscopy analysis allowed us to further clarify the mechanisms and complexity of the neutral salt actions on protein structures which may lead to strategies preventing unwelcome misfolding of proteins.
Highlights
The effect of neutral salts on protein structures and folding-unfolding events is of particular interest because neutrals salts are widely used in molecular biology to modulate the stability and association of proteins, as well as their salting-out and crystallization [1,2]
By using FTIR spectroscopy, we have shown that a second derivative method was suitable for detecting and quantification the small changes in the secondary structure of the human serum albumin (HSA) depending on different denaturing agents [31]
In this work by using this FTIR spectroscopy approach, we studied the effects of neutral salts KSCN, KCl, and (NH4)2SO4 on the secondary structure and thermostability of two different proteins
Summary
The effect of neutral salts on protein structures and folding-unfolding events is of particular interest because neutrals salts are widely used in molecular biology to modulate the stability and association of proteins, as well as their salting-out and crystallization [1,2]. The modern version of the anionic and cationic Hofmeister series are SO42−, HPO42−, acetate, citrate, Cl−, NO3−, ClO3−, I−, ClO4−, SCN, and NH4+, K+, Na+, Li+, Mg2+, Ca2+, guanidinium, respectively [6]. These series’ rank the power of the ion effect on the solubility of proteins and their stability
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