Title
α-Lactalbumin and sodium dodecyl sulfate aggregates: Denaturation, complex formation and time stability
Author
Yang Sun, Pedro L. Oseliero Filho, Cristiano L.P. Oliveira
Year
2017
Journal
Food Hydrocolloids
Abstract
We have combined isothermal titration calorimetry (ITC), spectroscopy and small-angle X-ray scattering (SAXS) to describe the denaturation process of bovine α-lactalbumin (BLA) induced by sodium dodecyl sulfate (SDS). As presented in the article, in the initial binding step, association of ∼6 SDS molecules with one protein molecule leads to a decrease on the hydrophobic environment of tryptophan residues and to an increase on the α-helix content of the protein, showing the endothermic effect of the whole process. Subsequently, binding of 30 SDS molecules with a BLA dimer leads to the highest α-helix content along with an exothermal behavior: at this point the SDS-BLA complexes can be described as core-shell like structures, also known as decorated micelles. At the end, binding of 55 SDS molecules forms a larger decorated micelle bound to a single BLA molecule in a molten globule state. After 600 h incubation, samples with SDS/BLA ratios of 21.7 and 43.2 shows a conversion of α-helix into disordered structures and the formation aggregates, while samples with SDS/BLA ratios of 3.4 and 78.3 exhibit an increased helical conformation with no aggregation. Based on SAXS analysis, the aggregates could be described as a structure of individual core-shell ellipsoidal SDS-BLA complexes connected in a beads-on-a-string structure. The results presented in this work not only provide overall information on SDS/BLA complexation, but also help on a better understanding about the roles of SDS concentration and incubation time on the α-helix content and aggregation/fibrillation process during protein denaturation.
Instrument
J-715
Keywords
Circular dichroism, Secondary structure, Tertiary structure, Vesicle interactions, Biochemistry, Food science