Tailoring thermal treatment to form liprotide complexes between oleic acid and different proteins

Liprotides are protein-lipid complexes in which the fatty acids form a micelle-like core surrounded by a shell of partially unfolded protein molecules. These complexes can be formed in different ways. The simplest approach is a thermal treatment where protein and fatty acid are mixed and then incubated at elevated temperatures. Using this approach we here demonstrate that we can monitor liprotide formation in real time using Small-Angle X-ray Scattering (SAXS). Optimal conditions for liprotide formation, i.e. temperature and incubation times, as well as liprotide stability and structure, vary for different proteins. The apo form of α-lactalbumin (aLA) forms liprotides at room temperature, however, Ovalbumin (Ova) and Bovine Serum Albumin (BSA) require elevated temperatures (≥60°C) to form liprotides, and in addition, they need to be returned to lower temperatures to remain stable; repeated cycles of heating and cooling gradually dissociate the liprotides in parallel with the formation of disulfide-bonded aggregates. Real-time tracking of the formation of liprotides of BSA or Ova with OA at 60–65°C showed that liprotide formation takes place within a period of 12–18min and is preceded by a loss of secondary structure of the protein and binding of OA to the protein. Our SAXS-based approach provides a straightforward strategy to optimize liprotide formation for a wide range of different proteins. [Display omitted] •Liprotides can be formed by thermally unfolding proteins together with fatty acids.•We can follow liprotide formation in real time with Small Angle X-ray Scattering.•For stably folded proteins, secondary structure loss precedes liprotide formation.•Different thermal profiles give rise to different liprotides.•Repeated cycles of heating and cooling destabilize liprotides via chemical changes.