Investigation of the effect of oxidation on the structure of β-lactoglobulin by high resolution mass spectrometry

Insight into the oxidation mechanism of coconut globulin by atmospheric cold plasma focusing on side chain amino acids

Atmospheric cold plasma (ACP), a novel non-thermal processing technology, generates active substances that stimulate protein oxidation in protein-based foods. Nevertheless, the precise mechanism through which ACP initiates amino acid oxidation on protein side chains remains ambiguous. This study primarily aimed to elucidate the mechanism of ACP-induced oxidation of coconut globulin, focusing on the process of amino acid oxidation. Analysis of protein oxidation products indicated a positive correlation between the extent of protein oxidation and the voltage and duration of ACP treatment. By analyzing the composition of amino acids and active ingredients, the study identified that the most significant changes amino acids were methionine, cysteine, and arginine, and •OH was the primary free radicals. The findings from oxidation kinetics and dynamic simulation indicated that •OH predominantly oxidized methionine, followed by L-cysteine and L-arginine. These results offer theoretical framework for understanding protein oxidation by ACP and suggest potential applications in protein-based food.

Exploring the interaction mechanism between the programmed death-ligand 1 protein and scutellarin via multi-spectroscopy and computer simulation

The programmed death-ligand 1 (PD-L1) protein plays a key role in immune responses. Scutellarin (SCU), as a flavonoid, has a variety of bioactivities. In this study, the human PD-L1 was obtained by expression and purification, and the interaction mechanisms between PD-L1 and SCU were revealed through multi-spectroscopy and computer simulation. Fluorescence data indicated that the quenching of PD-L1 by SCU was mainly static quenching, and primarily driven by hydrogen bonding and van der Waals forces. The binding constant (Ka) was decreased from 2.05 ± 0.55 × 104 L·mol-1 to 0.28 ± 0.08 × 104 L·mol-1 with increasing temperature. Meanwhile, the changes in the microenvironment of PD-L1 were revealed by the synchronous and the 3D fluorescence data. In addition, the melting temperature of PD-L1 increased by 1.67 °C after binding with SCU. Moreover, the circular dichroism data showed that SCU changed the secondary structure of PD-L1 by increasing α-helix content and decreasing β-sheet content. Furthermore, the binding modes between SCU and PD-L1 and the key residues involved in the interaction were revealed by molecular docking and molecular dynamics. These findings supported SCU as an alternative ICB therapeutic strategy and provided evidence for computer-based drug design strategies.

Thermal-induced interactions between soy protein isolate and malondialdehyde: Effects on protein digestibility, structure, and formation of advanced lipoxidation end products

Thermally processed lipid- and protein-rich foods have sparked widespread concern since they may degrade food nutrition and even risk food safety. This study investigated soy protein isolate (SPI) alterations of digestibility and structure, as well as the formation of potentially hazardous chemicals, i.e., advanced lipoxidation end products (ALEs), after interacting with malondialdehyde (MDA, a lipid oxidation product) under high-temperature cooking conditions (100-180 °C, up to 60 min). In-vitro protein digestion of the SPI-MDA mixtures suggested that their room-temperature interactions damaged SPI digestibility, and increasing the temperature and the duration of the thermal treatment exacerbated the adverse effects. Protein oxidation, covalent aggregation of subunits, and changes in secondary and tertiary structures were revealed using thiol quantification, gel electrophoresis, fluorescence spectroscopy, and circular dichroism (CD) spectra, which could explain reduced protein digestibility. High-resolution mass spectrometry (HRMS) identified seven non-crosslinked ALEs and two crosslinked ALEs. Increased MDA concentrations promoted the generation of ALEs. Moreover, the acrolein-derived ALEs with reactive carbonyl groups were prone to further reacting into crosslinked ALEs, potentially responsible for the subunit aggregation.

Specific detection of protein carbonylation sites by 473 nm photodissociation mass spectrometry

The study of protein oxidation remains a challenge despite the biomedical interest in reliable biomarkers of oxidative stress. This is particularly true for carbonylations although, recently, liquid chromatography-mass spectrometry techniques (LC-MS) have been proposed to detect this non-enzymatic and poorly distributed oxidative modification of proteins using untargeted or carbonyl-reactive probe methods. These methods proved to be feasible but could not preserve the dynamic range of the protein sample, making it impossible to quantify oxidatively modified proteoforms compared with native proteoforms. Here, we propose an innovative method based on the implementation of a reactive carbonyl probe conjugated with a laser-sensitive chromophore, dabcyl-aminooxy, which confers optical specificity to the LC-MS approach. In addition, our protein carbonyl detection method allows us to localize individual carbonylation sites by observing fragments of derivatized oxidized peptides. Two model proteins, alpha-synuclein and beta-lactoglobulin, were oxidized and carbonylation sites were detected, resulting in the identification of respectively 34 and 77 different carbonylated amino acids. Thus, we demonstrated the application of a direct and sensitive method for studying protein carbonylation sites in complex protein extracts.

Investigation of the Mechanism of 60Co Gamma-Ray Irradiation-Stimulated Oxidation Enhancing the Antigenicity of Ovalbumin by High-Resolution Mass Spectrometry

⁶⁰Co gamma-ray irradiation-induced antigenicity changes in ovalbumin (OVA) were investigated, and the molecular mechanism was analyzed. Irradiation treatment at 0-100 kGy could significantly enhance the IgG/IgE binding ability of OVA in a dose-dependent paradigm by concomitant oxidative modification, which exhibited color browning and an increase in carbonyl content caused by high-penetrable rays. More allergenic epitopes of OVA were exposed after irradiation treatment reflected by structural changes including the unfolding of tertiary structure, the conversion of α-helix structures to β-sheet and random coil structures, and the cleavage of several peptide bonds. Meanwhile, three oxidation sites of K46, T49, and N260 located in key linear epitopes were observed, which might increase the allergenic ability of OVA via the disaggregation of noncovalent bonds and the unwinding of α-helix structures. Conclusively, irradiation may enhance the potential allergenicity of OVA by oxidative modification, which provides theoretical guidance for effectively controlling the oxidation of proteins in the irradiation process.

Lipid oxidation induced egg white protein foaming properties enhancement: The mechanism study revealed by high resolution mass spectrometry

Lipid oxidation often occurs during egg white protein (EWP) storage and processing periods. Here, 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) was performed to simulate lipid oxidation to probe the oxidation effects on foaming and structural properties of EWP. Results indicated that EWP structure became unfolding and flexible after oxidation, resulting in more hydrophobic groups and negative charge exposed and soluble aggregates formed, which revealed by the results of DLS and AFM. Additionally, high resolution mass spectrometry results evidenced that ovotransferrin and lysozyme trended to be new oxidation targets with the AAPH concentration increasing, and the oxidation sites inside lysozyme proved that EWP unfolding and exposure of internal hydrophobic amino acids, which were related to the enhancement of EWP foaming properties. Overall, our study provided a further analysis of the lipid induced oxidation of EWP, which may contribute to provide a more accurate strategy for enhancing protein foaming properties in food industry.

pH-Dependent complexation between β-lactoglobulin and lycopene: Multi-spectroscopy, molecular docking and dynamic simulation study

This study aims to investigate the effect of pH levels (pH 7.0 and pH 8.1) on binding ability of β-lactoglobulin (β-LG) with lycopene (LYC) and elucidate interaction mechanisms using multi-spectroscopy and molecular docking study. β-LG at pH 8.1 showed a stronger binding affinity to lycopene than that at pH 7.0 according to binding constant, binding number, energy transfer efficiency, and surface hydrophobicity. Lycopene bound to protein mainly by van der Waals force in the form of static quenching mode and preferred to interact with β-LG at the top of barrel for both pH levels. Molecular dynamic simulation revealed that β-LG/LYC complex at pH 8.1 was more stable than at pH 7.0. β-LG/LYC complexes formed at pH 8.1 showed significantly higher ABTS radical scavenging activity than samples at pH 7.0 (p < 0.05). Data obtained may contribute valuable information for preparing a whey protein-based delivery system for lycopene.