Paper of the Month: August Edition
Although surfactant-protein interactions are ubiquitous in the food and cosmetics industry and fundamental for the mode of action of cleaning detergents, they are still not fully understood. To obtain a more detailed picture of how surfactants induce protein denaturation, the mechanism of unfolding of Ca2+-depleted α-lactalbumin (aLA) by SDS was investigated in this paper by combining stopped-flow mixing of the protein and surfactant solutions, using the Chirascan SF.3 accessory, with stopped-flow synchrotron small-angle X-ray scattering (SAXS), circular dichroism and Trp fluorescence, together with information from previous calorimetric studies. The unfolding kinetics was dissected at the level of both protein and surfactant to show that a protein-surfactant complex is formed within the dead time of mixing. In two kinetic steps, first a cluster of SDS molecules binds asymmetrically, after which aLA redistributes around the SDS cluster. The rapid unfolding of aLA was attributed to its predominantly α-helical structure, which persists in SDS, enabling aLA to unfold without undergoing major secondary structural changes unlike β-sheet rich proteins.
Jensen, Pedersen, Otzen, and Pedersen. 2020. “Multi-Step Unfolding and Rearrangement of α-Lactalbumin by SDS Revealed by Stopped-Flow SAXS.” Frontiers in Molecular Biosciences 7: 1-12.
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