Issue 34, 2020

SDS-induced multi-stage unfolding of a small globular protein through different denatured states revealed by single-molecule fluorescence

Abstract

Ionic surfactants such as sodium dodecyl sulfate (SDS) unfold proteins in a much more diverse yet effective way than chemical denaturants such as guanidium chloride (GdmCl). But how these unfolding processes compare on a molecular level is poorly understood. Here, we address this question by scrutinising the unfolding pathway of the globular protein S6 in SDS and GdmCl with single-molecule Förster resonance energy transfer (smFRET) spectroscopy. We show that the unfolding mechanism in SDS is strikingly different and convoluted in comparison to denaturation in GdmCl. In contrast to the reversible two-state unfolding behaviour in GdmCl characterised by kinetics on the timescale of seconds, SDS demonstrated not one, but four distinct regimes of interactions with S6, dependent on the surfactant concentration. At ≤1 mM SDS, S6 and surfactant molecules form quasi-micelles on a minute timescale; at millimolar [SDS], the protein denatures through an unfolded/denatured ensemble of highly heterogeneous states on a multi-second timescale; at tens of millimolar of SDS, the protein unfolds into a micelle-packed conformation on the second timescale; and >50 mM SDS, the protein unfolds with millisecond timescale dynamics. We propose a detailed model for multi-stage unfolding of S6 in SDS, which involves at least three different types of denatured states with different level of compactness and dynamics and a continually changing landscape of interactions between protein and surfactant. Our results highlight the great potential of single-molecule fluorescence as a direct probe of nanoscale protein structure and dynamics in chemically complex surfactant environments.

Graphical abstract: SDS-induced multi-stage unfolding of a small globular protein through different denatured states revealed by single-molecule fluorescence

Supplementary files

Article information

Article type
Edge Article
Submitted
14 Apr 2020
Accepted
07 Aug 2020
First published
10 Aug 2020
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2020,11, 9141-9153

SDS-induced multi-stage unfolding of a small globular protein through different denatured states revealed by single-molecule fluorescence

G. Krainer, A. Hartmann, V. Bogatyr, J. Nielsen, M. Schlierf and D. E. Otzen, Chem. Sci., 2020, 11, 9141 DOI: 10.1039/D0SC02100H

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