Α-Lactalbumin and sodium dodecyl sulfate aggregates: Denaturation, complex formation and time stability. (January 2017)

• Record Type: Journal Article
• Authors: Sun, Yang; Oseliero Filho, Pedro L.; Oliveira, Cristiano L.P.
• Is Part Of: Food hydrocolloids. Volume 62(2017)
• Page Start: 10
• Page End: 20
• Publication Date: 2017-01
• Subjects: Bovine α-lactalbumin -- SDS-induced helix -- Denaturation -- SAXS -- Decorated core-shell structure -- Aggregation; Hydrocolloids -- Periodicals; Food additives -- Periodicals; Colloïdes -- Périodiques; Aliments -- Additifs -- Périodiques; Colloids; Food additives; Periodicals; Electronic journals; 664.06
• DOI: 10.1016/j.foodhyd.2016.07.031
• Languages: English
• ISSNs: 0268-005X

Abstract

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. Graphical abstract: Schematic representation of the different stages of SDS–BLA binding. Highlights: The denaturation of BLA induced by SDS was characterized using a spectroscopic, calorimetric and scattering techniques. The formation of SDS induced α-helix is described and explained. The structure of SDS/BLA complexes present interesting dependency on the SDS/BLA ratio. The secondary structure of BLA when complexed with SDS shows an interesting time dependency.