Role of Charge and Hydrophobicity in Liprotide Formation: A Molecular Dynamics Study with Experimental Constraints. (9th January 2018)

• Record Type: Journal Article
• Authors: Nedergaard Pedersen, Jannik; Frederix, Pim Wilhelmus Johannes Maria; Skov Pedersen, Jan; Marrink, Siewert Jan; Otzen, Daniel E.
• Is Part Of: Chembiochem. Volume 19:Number 3(2018)
• Page Start: 263
• Page End: 271
• Publication Date: 2018-01-09
• Subjects: alpha-lactalbumin -- fatty acids -- molecular dynamics -- oleate -- proteins; Biochemistry -- Periodicals; Molecular biology -- Periodicals; Pharmaceutical chemistry -- Periodicals; 572
• DOI: 10.1002/cbic.201700496
• Languages: English
• ISSNs: 1439-4227

Abstract

Abstract: Bovine α‐lactalbumin (aLA) and oleate (OA) form a complex that has been intensively studied for its tumoricidal activity. Small‐angle X‐ray scattering (SAXS) has revealed that this complex consists of a lipid core surrounded by partially unfolded protein. We call this type of complex a liprotide. Little is known of the molecular interactions between OA and aLA, and no technique has so far provided any high‐resolution structure of a liprotide. Here we have used coarse‐grained (CG) molecular dynamics (MD) simulations, isothermal titration calorimetry (ITC) and SAXS to investigate the interactions between aLA and OA during the process of liprotide formation. With ITC we found that the strongest enthalpic interactions occurred at a molar ratio of 12.0±1.4:1 OA/aLA. Liprotides formed between OA and aLA at several OA/aLA ratios in silico were stable both in CG and in all‐atom simulations. From the simulated structures we calculated SAXS spectra that show good agreement with experimentally measured patterns of matching liprotides. The simulations showed that aLA assumes a molten globular (MG) state, exposing several hydrophobic patches involved in interactions with OA. Initial binding of aLA to OA occurs in an area of aLA in which a high amount of positive charge is located, and only later do hydrophobic interactions become important. The results reveal how unfolding of aLA to expose hydrophobic residues is important for complex formation between aLA and OA. Our findings suggest a general mechanism for liprotide formation and might explain the ability of a large number of proteins to form liprotides with OA. Abstract : Complexes of proteins and fatty acids —termed liprotides—form structures based on a lipid core surrounded by partially disordered protein. Molecular dynamics simulation of these complexes can help in achieving better understanding of the protein–lipid interactions. Combining the in silico method with experimental measurements helped to validate the approach and provided further structural insight into liprotides.