Abstract
It was shown that at low concentrations guanidine hydrochloride (GdnHCl) can cause aggregation of proteins in partially folded state and that fluorescent dye 1-anilinonaphthalene-8-sulfonic acid (ANS) binds with these aggregates rather than with hydrophobic clusters on the surface of protein in molten globule state. That is why the increase in ANS fluorescence intensity is often recorded in the pathway of protein denaturation by GdnHCl, but not by urea. So what was previously believed to be the molten globule state in the pathway of protein denaturation by GdnHCl, in reality, for some proteins represents the aggregates of partially folded molecules.
Highlights
Protein unfolding induced by chemical denaturants such as urea and guanidine hydrochloride (GdnHCl) is a common approach to study protein folding in vitro [1]
It has been shown that low concentrations of GdnHCl can cause protein stabilization by eliminating the strains in protein caused by the electrostatic interactions of charged groups on its surface [2,3]
The account of this effect clarifies why the transition of some proteins (e.g. a-lactalbumine and carbonic anhydrase II (CA II)) into intermediate state like molten globule is accompanied by blue shift of fluorescence spectrum, increase in anisotropy of intrinsic fluorescence, and increase in fluorescence of hydrophobic dye 1anilinonaphthalene-8-sulfonic acid (ANS) when denaturation is caused by GdnHCl but not by urea [5,7,8]
Summary
Protein unfolding induced by chemical denaturants such as urea and guanidine hydrochloride (GdnHCl) is a common approach to study protein folding in vitro [1]. In this case the effect is especially pronounced because in aggregation are involved large supramolecular complexes of inactivated actin [11,12] and it is accompanied by the increase in ANS fluorescence intensity, but by the increase in light scattering .
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