Probing the role of ortho-dihydroxy groups on lysozyme fibrillation

Experimental and theoretical studies on the anti-amyloidogenic and destabilizing effects of pyrogallol against human insulin protein

One of the major problems caused by repeated subcutaneous insulin injections in patients with diabetes is insulin amyloidosis. Understanding the molecular mechanism of amyloid fibril formation of insulin and finding effective compounds to inhibit or eliminate them is very important, and extensive research has been done on it. In this study, the anti-amyloidogenic and destabilizing effects of the pyrogallol, as a phenolic compound, on human insulin protein were investigated by CR absorbance, ThT and ANS fluorescence, FTIR spectroscopy, and atomic force microscopy. According to the obtained results, the formation of amyloid fibrils at pH 2.0 and 50°C was confirmed by CR, ThT, ANS, and FTIR assays. Microscopic images also showed the twisted and long structures of amyloid fibrils. Simultaneous incubation of the protein with pyrogallol at different concentrations reduced the intensities of CR, ThT, and ANS in a dose-dependent manner, and no trace of fibrillar structures was observed in the microscopic images. FTIR spectroscopy also showed that the position of the amide I band in the spectrum of samples containing pyrogallol was shifted. Based on the findings of this study, it can be concluded that pyrogallol can be effective in preventing and suppressing human insulin amyloid fibrils. PRACTICAL APPLICATIONS: In recent years, finding a strategy for the treatment of amyloid diseases has been considered by many researchers. Targeting protein aggregates by small organic molecules such as polyphenols is one of the most desirable and effective strategies to prevent and improve amyloid disease, which has received much attention in recent years. 1,2,3-Trihydroxybenzene, commonly known as pyrogallol (Py), is a phenolic compound like other natural polyphenols that are present in human food sources, including fruits and vegetables, and a variety of edible and medicinal plants. So far, many beneficial activities for pyrogallol such as anti-cancer, antioxidant, antibacterial, antiviral, and antifungal have been reported in various studies. Since various studies have shown that natural polyphenols have special properties to prevent amyloid disease, the present study could be useful in advancing the design purposes of new anti-amyloid drugs in the future.

Modification with N-benzylisatin restricts stress-induced aggregation of hen egg white lysozyme: Anti-amyloidogenic property of isatin derivative with possible clinical implications

Hen egg white lysozyme (HEWL) is a structural homolog of human lysozyme and is widely used as a model protein to investigate protein aggregation. The effect of N-benzylisatin on stress-induced aggregation of HEWL has been investigated in the present study. Interaction of the isatin derivative with HEWL induced changes in protein secondary and tertiary structural conformation as evident from different biophysical and spectroscopic studies. In addition, modification with N-benzylisatin was found to increase the conformational stability of HEWL and afford considerable resistance to the protein to stress-induced aggregation as indicated from subsequent experimental studies, including thioflavin T fluorescence, microscopic imaging and dynamic light scattering analysis. Protein modification was analysed and confirmed by MALDI-TOF and ESI-MS studies. The results highlight possible clinical implications of isatin derivative in the treatment of protein misfolding and conformational disorders.

Fungal laccase-triggered 17β-estradiol humification kinetics and mechanisms in the presence of humic precursors

Naturally-occurring phenolic acids (PAs) act as humic precursors that participate in the conversion behaviors and coupling pathways of steroidal estrogens (SEs) during laccase-triggered humification processes (L-THPs). Herein, the influences and mechanisms of PAs on Trametes versicolor laccase-evoked 17β-estradiol (E2) conversion kinetics and humification routes were explored. Fungal laccase was fleet in converting > 99% of E2, and the calculated pseudo-first-order velocity constant and half-time values were respectively 0.039 min^-1 and 17.906 min. PAs containing an O-dihydroxy moiety such as gallic acid and caffeic acid evidently hampered E2 humification owning to the yielded highly reactive O-quinones reversed E2 radicals by hydrogen transfer mechanism, implying that the inhibition effect was enormously dependent upon the number and position of the phenolic -OH present in humic precursors. Oligomers and polymers with carbon-carbon/oxygen links were tentatively found as E2 main humified species resulting from laccase-evoked successive oxidative-coupling. Note that PAs participating in the humification also encountered oxydehydrogenation, self-polymerization, and cross-binding to E2. Interestingly, the -COOH and -OCH₃ groups of PAs could be deprived in radical-caused self/co-polymerization. The generation of humified products not only circumvented the environmental risks of parent compounds but accelerated global carbon sequestration. To our knowledge, this is the first in-depth revelation of the humification pathways and related mechanisms of SEs with humic precursors in aquatic ecosystems by L-THPs.

Gallic acid oxidation products alter the formation pathway of insulin amyloid fibrils

Amyloidogenic protein assembly into insoluble fibrillar aggregates is linked with several neurodegenerative disorders, such as Alzheimer’s or Parkinson’s disease, affecting millions of people worldwide. The search for a potential anti-amyloid drug has led to the discovery of hundreds of compounds, none of which have passed all clinical trials. Gallic acid has been shown to both modulate factors leading to the onset of neurodegenerative disorders, as well as directly inhibit amyloid formation. However, the conditions under which this effect is seen could lead to oxidation of this polyphenol, likely changing its properties. Here we examine the effect of gallic acid and its oxidised form on the aggregation of a model amyloidogenic protein–insulin at low pH conditions. We show a vastly higher inhibitory potential of the oxidised form, as well as an alteration in the aggregation pathway, leading to the formation of a specific fibril conformation.

Study of the noncovalent interactions between phenolic acid and lysozyme by cold spray ionization mass spectrometry (CSI-MS), multi-spectroscopic and molecular docking approaches

Elucidating the recognition mechanisms of the noncovalent interactions between pharmaceutical molecules and proteins is important for understanding drug delivery in vivo, and for the further rapid screening of clinical drug candidates and biomarkers. In this work, a strategy based on cold spray ionization mass spectrometry (CSI-MS), combined with fluorescence, circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), and molecular docking methods, was developed and applied to the study of the noncovalent interactions between phenolic acid and lysozyme (Lys). Based on the real characterization of noncovalent complex, the detailed binding parameters, as well as the protein conformational changes and specific binding sites could be obtained. CSI-MS and tandem mass spectrometry (MS/MS) technique were used to investigate the phenolic acid-Lys complexes and the structure-affinity relationship, and to assess their structural composition and gas phase stability. The binding affinity was obtained by direct and indirect MS methods. The fluorescence spectra showed that the intrinsic fluorescence quenching of Lys in solution was a static quenching mechanism caused by complex formation, which supported the MS results. The CD and FTIR spectra revealed that phenolic acid changed the secondary structure of Lys and increased the α-helix content, indicating an increase in the tryptophan (W) hydrophobicity near the protein binding site resulting in a conformational alteration of the protein. In addition, molecular docking studies were performed to investigate the binding sites and binding modes of phenolic acid on Lys. This strategy can more comprehensively and truly characterize the noncovalent interactions and can guide further research on the interactions of phenolic acid with other proteins.

Methylglyoxal modification reduces the sensitivity of hen egg white lysozyme to stress-induced aggregation: Insight into the anti-amyloidogenic property of α-dicarbonyl compound

The reactive α-oxoaldehyde, methylglyoxal reacts with different proteins to form Advanced Glycation End Products (AGEs) through Maillard reaction. Its level increases significantly in diabetic condition. Here, we have investigated the effect of different concentrations of methylglyoxal (200-400 µM) on the monomeric protein, hen egg white lysozyme (HEWL) following incubation for 3 weeks. Reaction of methylglyoxal with HEWL induced considerable changes in tertiary structure of the protein, but no significant alteration in secondary structure, as evident from different spectroscopic and biophysical studies. Interestingly, methylglyoxal modification was found to enhance the thermal stability of the protein and reduce its sensitivity to stress-induced aggregation. Finally, peptide mass fingerprinting revealed modification of arginine (Arg-45, Arg-14, Arg-68 or Arg-72) and lysine (Lys-116) residues of the protein to AGE adducts, namely, hydroimidazolone, tetrahydropyrimidine, and carboxyethyllysine. Methylglyoxal-derived AGE adducts (MAGE) appear to be responsible for the observed changes in protein. As demonstrated in the present study, the findings may highlight a possible therapeutic potential of the α-oxoaldehyde against protein misfolding and conformational disorder.Communicated by Ramaswamy H. Sarma.

Inhibition of lysozyme fibrillogenesis by hydroxytyrosol and dopamine: An Atomic Force Microscopy study

Protein aggregation underlies many human diseases characterized by the deposition of normally soluble proteins in both fibrillar and amorphous aggregates. Here, Atomic Force Microscopy (AFM) has been applied to investigate the ability to inhibit hen egg white lysozyme (HEWL) fibrillogenesis by hydroxytyrosol (HT), one of the main phenolic components of olive oil. In this framework, HEWL is a useful and well-studied model protein whose amyloid-like fibril formation can be induced under experimental conditions where HT is more stable. HEWL fibrils, obtained at pH 1.6 and at 65 °C, exhibited a height of about 3 nm and a fibril length on average of about 3 μm. The presence of HT reduced the HEWL fibril number and length with respect to the control sample. Interestingly, also dopamine, a compound with a chemical structure similar to HT, decreased both the fibril number and the fibril length. AFM experimental data were supported by Thioflavin T assay and Fourier transform infrared spectroscopy. Our results show that HT is an effective inhibitor of HEWL aggregation, thus suggesting possible future applications of this natural compound for potential prevention or treatment of amyloid diseases, or as a lead molecular structure for the design of improved modulators.