Role of lysine epsilon-amino groups of beta-lactoglobulin on its activating effect of Kluyveromyces lactis beta-galactosidase

Probing the modulated formation of gold nanoparticles-beta-lactoglobulin corona complexes and their applications

Understanding the interactions between proteins and nanoparticles (NPs) along with the underlying structural and dynamic information is of utmost importance to exploit nanotechnology for biomedical applications. Upon adsorption onto a NP surface, proteins form a well-organized layer, termed the corona, that dictates the identity of the NP-protein complex and governs its biological pathways. Given its high biological relevance, in-depth molecular investigations and applications of NPs-protein corona complexes are still scarce, especially since different proteins form unique corona patterns, making identification of the biomolecular motifs at the interface critical. In this work, we provide molecular insights and structural characterizations of the bio-nano interface of a popular food-based protein, namely bovine beta-lactoglobulin (β-LG), with gold nanoparticles (AuNPs) and report on our investigations of the formation of corona complexes by combined molecular simulations and complementary experiments. Two major binding sites in β-LG were identified as being driven by citrate-mediated electrostatic interactions, while the associated binding kinetics and conformational changes in the secondary structures were also characterized. More importantly, the superior stability of the corona led us to further explore its biomedical applications, such as in the smartphone-based point-of-care biosensing of Escherichia coli (E. coli) and in the computed tomography (CT) of the gastrointestinal (GI) tract through oral administration to probe GI tolerance and functions. Considering their biocompatibility, edible nature, and efficient excretion through defecation, AuNPs-β-LG corona complexes have shown promising perspectives for future in vitro and in vivo clinical settings.

Oxidative damage to food and human serum proteins: Radical-mediated oxidation vs. glyco-oxidation

This study compared a hydroxyl radical-generating system (HRGS) (0.05-0.2mM Fe³⁺+0.6mM H₂O₂) and a glycation system (GLY) (0.05-0.2mM Fe³⁺+0.05M glucose) for their ability to promote protein carbonylation and tryptophan depletion in myofibrillar proteins, ovalbumin, β-lactoglobulin, soy protein and human serum albumin. Animal-source were more susceptible to protein carbonylation than soy proteins and globular were more susceptible than fibrillar proteins. Both systems promoted tryptophan loss and the formation of protein carbonyls and iron had a clear dose-effect in most systems and proteins. In the tested conditions, the GLY environment was more effective than the HRGS system in promoting the oxidative damage to food proteins. According to the results, glucose and H₂O₂ may compete for iron for the production of glycosylative and oxidative species, respectively. This study provides original insight into the chemical mechanisms implicated in the oxidative and glycosylative damage to food proteins.

β-lactoglobulin's conformational requirements for ligand binding at the calyx and the dimer interphase: a flexible docking study

β-lactoglobulin (BLG) is an abundant milk protein relevant for industry and biotechnology, due significantly to its ability to bind a wide range of polar and apolar ligands. While hydrophobic ligand sites are known, sites for hydrophilic ligands such as the prevalent milk sugar, lactose, remain undetermined. Through the use of molecular docking we first, analyzed the known fatty acid binding sites in order to dissect their atomistic determinants and second, predicted the interaction sites for lactose with monomeric and dimeric BLG. We validated our approach against BLG structures co-crystallized with ligands and report a computational setup with a reduced number of flexible residues that is able to reproduce experimental results with high precision. Blind dockings with and without flexible side chains on BLG showed that: i) 13 experimentally-determined ligands fit the calyx requiring minimal movement of up to 7 residues out of the 23 that constitute this binding site. ii) Lactose does not bind the calyx despite conformational flexibility, but binds the dimer interface and an alternate Site C. iii) Results point to a probable lactolation site in the BLG dimer interface, at K141, consistent with previous biochemical findings. In contrast, no accessible lysines are found near Site C. iv) lactose forms hydrogen bonds with residues from both monomers stabilizing the dimer through a claw-like structure. Overall, these results improve our understanding of BLG's binding sites, importantly narrowing down the calyx residues that control ligand binding. Moreover, our results emphasize the importance of the dimer interface as an insufficiently explored, biologically relevant binding site of particular importance for hydrophilic ligands. Furthermore our analyses suggest that BLG is a robust scaffold for multiple ligand-binding, suitable for protein design, and advance our molecular understanding of its ligand sites to a point that allows manipulation to control binding.