Decoding the Structure-Function Relationship of the Muramidase Domain in E. coli O157.H7 Bacteriophage Endolysin: A Potential Building Block for Chimeric Enzybiotics.

Bacteriophage endolysins are potential alternatives to conventional antibiotics for treating multidrug-resistant gram-negative bacterial infections. However, their structure-function relationships are poorly understood, hindering their optimization and application. In this study, we focused on the individual functionality of the C-terminal muramidase domain of Gp127, a modular endolysin from E. coli O157:H7 bacteriophage PhaxI. This domain is responsible for the enzymatic activity, whereas the N-terminal domain binds to the bacterial cell wall. Through protein modeling, docking experiments, and molecular dynamics simulations, we investigated the activity, stability, and interactions of the isolated C-terminal domain with its ligand. We also assessed its expression, solubility, toxicity, and lytic activity using the experimental data. Our results revealed that the C-terminal domain exhibits high activity and toxicity when tested individually, and its expression is regulated in different hosts to prevent self-destruction. Furthermore, we validated the muralytic activity of the purified refolded protein by zymography and standardized assays. These findings challenge the need for the N-terminal binding domain to arrange the active site and adjust the gap between crucial residues for peptidoglycan cleavage. Our study shed light on the three-dimensional structure and functionality of muramidase endolysins, thereby enriching the existing knowledge pool and laying a foundation for accurate in silico modeling and the informed design of next-generation enzybiotic treatments.

Structural insights into the pathogenicity of point mutations in human acyl-CoA dehydrogenase homotetramers.

Acyl-CoA dehydrogenase deficiency (ACAD) is an inherited and potentially fatal disorder with variable clinical symptoms. The relationship between pathogenicity and deleterious point mutations is investigated here in ACAD structures of short (SCAD) and medium-chain (MCAD) types. Structures and dynamic features of native and mutant forms of enzymes models were compared. A total of 2.88 µs molecular dynamics simulations were performed at four different temperatures. Total energy, RMSD, protein ligand interactions and affinity, RMSF measures, secondary structure changes, and important interactions were studied. Mutations in the three main domains of ACADs are pathogenic, while those located at linker turns are not. Mutations affect mostly tetramer formations, secondary structures, and many contacts and interactions. In R206H (MCAD mutant) which is experimentally known to cause a huge turnover decrease, the lack of a single H-bond between substrate and FAD was observed. Secondary structures showed temperature-dependent changes, and SCAD activity was found to be highly correlated to the enzyme helix 3-10 content. Finally, RMSF patterns pointed to one important loop that maintains the substrate close to the active site and is a cause of substrate wobbling upon mutation. Despite similar structure, function, and cellular location, SCAD and MCAD may have different optimum temperatures that are related to the structure taken at that specific temperature. In conclusion, new insight has been provided on the effect of various SCAD and MCAD pathogenic mutations on the structure and dynamical features of the enzymes.

Correction to: Drug repurposing using computational methods to identify therapeutic options for COVID-19.

[This corrects the article DOI: 10.1007/s40200-020-00546-9.].

Chemical Modification of the Amino Groups of Human Insulin: Investigating Structural Properties and Amorphous Aggregation of Acetylated Species.

The efficacy of human recombinant insulin can be affected by its aggregation. Effects of acetylation were observed on insulin structure, stability, and aggregation at 37 and 50 °C and pH of 5.0 and 7.4 with the use of spectroscopy, circular dichroism (CD), dynamic light scattering (DLS), and atomic force microscopy (AFM). Raman and FTIR results were indicative of structural changes in AC-INS, and CD analyses showed a slight increase in ß-sheet content in AC-INS. Melting temperature (Tm) measurements indicated an overall more stable structure and spectroscopic assessment showed a more compact one. Formation of amorphous aggregates was followed over time and kinetics parameters showed a longer nucleation phase (higher t* amount) and lower aggregates amount (lower Alim) for acetylated insulin (AC-INS) compared to native (N-INS) in all tested conditions. The results of amyloid-specific probes approved the formation of amorphous aggregates. Size particle and microscopic analysis suggested that AC-INS was less prone to form aggregates, which were smaller if formed. In conclusion, this study has demonstrated that controlled acetylation of insulin may lead to its higher stability and lower propensity toward amorphous aggregation and has provided insight into the result of this type of post-translational protein modification.

Local Insulin-Derived Amyloidosis Model Confronted with Silymarin: Histological Insights and Gene Expression of MMP, TNF-α, and IL-6.

Amyloidosis is a heterogeneous group of protein deposition diseases associated with the presence of amyloid fibrils in tissues. Analogs of insulin that are used for treating diabetic patients (including regular insulin) can form amyloid fibrils, both in vitro and in vivo as reported in patients. The main purpose of this study was the induction of localized insulin-generated amyloidosis and the observation of silymarin effects on this process. In order to obtain amyloid structures, regular insulin was incubated at 37 °C for 24 h. Congo red absorbance and transmission electron microscopy images validated the formation of amyloid fibrils. Those fibrils were then injected subcutaneously into rats once per day for 6, 12 or 18 consecutive days in the presence or absence of silymarin, and caused development of firm waxy masses. These masses were excised and stained with Hematoxylin and Eosin, Congo red and Thioflavin S. Histological examination showed adipose cells and connective tissue in which amyloid deposition was visible. Amyloids decreased in the presence of silymarin, and the same effect was observed when silymarin was added to normal insulin and injected subsequently. Furthermore, plasma concentrations of MMP2, TNF-α, and IL-6 inflammatory factors were measured, and their gene expression was locally assessed in the masses by immunohistochemistry. All three factors increased in the amyloidosis state, while silymarin had an attenuating effect on their plasma levels and gene expression. In conclusion, we believe that silymarin could be effective in counteracting insulin-generated local amyloidosis.

Phenylalanine and indole effects on the pathogenicity of human lysozyme amorphous aggregates.

Protein aggregation can affect the stability and function of proteins, and may lead to developing diseases, but reports on the in vivo effect of aggregates are scarce. In the current study, the effect of phenylalanine (Phe) and indole presence was first investigated on the structure and stability of human lysozyme (HLZ) and its aggregation under in vitro condition. Tm measurements, circular dichroism and spectrofluorimetric spectra, as well as and transmission electron microscopy (TEM) were performed in this stage. In the next step, pathogenicity of HLZ amorphous aggregates formed in presence or absence of the additives was investigated in vivo, by subcutaneous injection to adult male Wistar rats. Resulting inflamed tissues were studied by hematoxylin and eosin (HE), Congo red and Sudan black staining. Serum levels of liver enzymes (Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST)), specific inflammatory cytokines (Tumor Necrosis Factor Alpha (TNF-α) and Interleukin 6 (IL-6)) as well as glucose, cholesterol, and triglyceride levels were measured. Amorphous aggregates of HLZ caused inflammation and affected the number of fat cells, macrophages, cytokines, liver enzymes and glucose. Indole, that increases amorphous aggregates amount as shown with CD, fluorescence, and TEM experiments, leads into more severe inflammation. In presence of Phe, (which stabilizes HLZ structure) a markedly milder inflammatory state is observed in histological results and no increase could be detected in the inflammation-related parameters. In conclusion, amorphous aggregates of HLZ may be pathogenic in vivo, and presence of anti-aggregation compounds (such as Phe) can be effective in diminishing their deleterious manifestations.

Structural modeling of human AKAP3 protein and in silico analysis of single nucleotide polymorphisms associated with sperm motility.

AKAP3 is a member of the A-kinase anchoring proteins and it is a constituent of the sperm fibrous sheath. AKAP3 is needed for the formation of sperm flagellum structure, sperm motility, and male fertility. This study aims to model the AKAP3 tertiary structure and identify the probable impact of four mutations characterized in infertile men on the AKAP3 structure. The T464S, I500T, E525K, and I661T substitutions were analyzed using in silico methods. The secondary structure and three-dimensional model of AKAP3 were determined using PSI-BLAST based secondary structure prediction and Robetta servers. The TM-score was used to quantitatively measure the structural similarities between native and mutated models. All of the desired substitutions were classified as benign. I-Mutant results showed all of the substitutions decreased AKAP3 stability; however, the I500T and I661T were more effective. Superposition and secondary structure comparisons between native and mutants showed no dramatic deviations. Our study provided an appropriate model for AKAP3. Destabilization of AKAP3 caused by these substitutions did not appear to induce structural disturbances. As AKAP3 is involved in male infertility, providing more structural insights and the impact of mutations that cause protein functional diversity could elucidate the etiology of male fertility problems at molecular level.

A study on alpha-terpineol in Alzheimer's disease with the use of rodent in vivo model, restraint stress effect and in vitro Amyloid beta fibrils

Abstract Alzheimer's disease (AD) is a neurological disorder in which the neuronal degeneration is associated with inflammatory processes and oxidative stress. Since alpha-terpineol was shown to possess antioxidant and anti-inflammatory effects, the administration of this compound was studied on a rat model of AD. To create this model, Aβ1-42 was injected into the hippocampus of male Wistar rats. Generated AD models were divided into simple AD models and AD models in which short-term immobilization stress was added. Preventive and therapeutic (post-AD induction) effects of alpha-terpineol consumption (100 mg/Kg) were subsequently investigated in AD models, which were compared with control groups. Biochemical factors (superoxide dismutase and malondialdehyde), histological manifestations (amyloid plaques and neuron counts) and possible memory impairment (shuttle-box experiment) were investigated in all groups. For the in vitro experiment, alpha-terpineol effect was checked on Aβ1-42 fibril formation. In preventive and therapeutic modes, alpha-terpineol consumption could improve neurogenesis and long-term memory while reducing amyloid plaque counts and ameliorating biochemical factors (higher levels of superoxide dismutase and malondialdehyde and reduced levels of MDA). In vitro, shorter fibrillar structures were formed in the presence of alpha-terpineol, which indicates an anti-amyloid effect for this compound. In conclusion, alpha-terpineol significantly counteracted AD consequences.

PAMAM and polyester dendrimers as favipiravir nanocarriers: a comparative study using DFT method.

The electronic sensitivity and reactivity of polyamidoamine (PAMAM) and polyester dendrimers toward favipiravir (T705) were inspected using density functional theory method. The T705 drug is adsorbed on the surface of PAMAM and polyester dendrimers with the binding energy of -27.26 and -26.80 kcal mol-1, respectively, in the solvent phase. The energy gap of PAMAM and polyester dendrimers reduced by about 32% and 27%, indicating that the electrical conductance of carriers become 8.16 × 1023 and 4.41 × 1022 times higher, upon T705 adsorption. The work function (Φ) value of PAMAM and polyester is changed about 1.53 and 0.71 eV, respectively. Thus, PAMAM dendrimer is about 2.5 times stronger Φ-type sensor than polyester dendrimer. The recovery time for T705 desorption from the PAMAM and polyester surface is predicted to be 9.2 × 103 and 4.2 × 103 s, respectively, at physiological environment.

Hydro alcoholic green tea extract effect on high fat diet treated NMRI mice and 3T3L1 cells.

PURPOSE: In order to counteract the obesity has epidemics, since current anti-obesity drugs effects remain limited, there is a need to provide new options. As a project aiming to assess potential anti obesity natural compounds, the effects of consumption of a minimal dose of green tea hydro alcoholic extract (GT) on adipocyte differentiation of 3T3L1 cell line were investigated. METHODS: Obesity was induced in female NMRI mice (which are less used overall) by the use of a high fat diet. Mice were divided into four groups of control (C), treated control (TC), obese (O) and treated obese (TO). TC and TO groups received 8 mg/Kg/day of GT for 8 weeks, and weighted weekly, after what biochemical and histological parameters were measured. GT was used at doses of 100,150 and 200 µg/ml on 3T3L1, and staining with Oil-red-O was done for estimation of fat droplet accumulation. RESULTS: Body weight was found to be affected significantly by GT. Blood glucose levels did not show significant changes between groups, while triglycerides levels of the O group was significantly higher than the C group, but the TO group showed no significant difference with the C group upon GT treatment. Liver and visceral fat tissues showed more normalized tissue and less fat accumulation in the TO group. TO and TC groups showed an ameliorated morphologic state of liver tissues. GT was also able to decrease fat droplet formation in a dose-dependent manner. CONCLUSIONS: Adding a minimal amount of GT to the daily consumption may have preventive effects on fat accumulation in healthy subjects, while in obese cases, GT shows significant therapeutic effect.

The therapeutic effects of berberine plus sitagliptin in a rat model of fatty liver disease.

OBJECTIVES: Fatty liver disease (FLD) is a disorder related to accumulation of excess fat within the hepatocytes. In this study, the effects of Berberine, a natural compound, and Sitagliptin as a DPP-4 inhibitor, were observed in a rat model of FLD. MATERIALS AND METHODS: Forty male rats were divided into five groups (n=6) including the control group (normal food and water), high-fat group (high-fat diet (HF) for 6 weeks), Berberine group (HF with oral administration of Berberine at 150 mg/kg for 6 weeks), Sitagliptin group (HF with oral administration of Sitagliptin at 10 mg/kg for 6 weeks), and Berberine/ Sitagliptin group (HF diet within combination with oral administration of Berberine 75 mg/kg and Sitagliptin 5 mg/kg for 6 weeks). Animals were examined for weight gain, serum and hepatic biochemical parameters, tissue histology, expression of glucose transporter type 4 (GLUT4) mRNA, and protein expression of Adiponectin receptor2 (AdipoR2) and extracellular signal-regulated kinase (ERK) and phoERK. RESULTS: The results showed that ALT, AST, lipid profile, insulin, glucose, MDA, and TNF-α were significantly improved in high-fat rats treated with Berberine/ Sitagliptin compared with HF and Sitagliptin, and Berberine alone groups. SOD and adiponectin levels in Berberine/ Sitagliptin group were also significantly increased compared with the other groups. Immunoblot analysis showed that the expression of pho-ERK/ERK was significantly decreased and expression of AdipoR2 significantly increased in the Berberine/ Sitagliptin group compared with other groups. CONCLUSION: Co-administration of Berberine and Sitagliptin is an effective therapeutic regimen for conditions associated with hyperlipidemia.

Modeling and simulation in medical sciences: an overview of specific applications based on research experience in EMRI (Endocrinology and Metabolism Research Institute of Tehran University of Medical Sciences).

The concomitant use of various types of models (in silico, in vitro, and in vivo) has been exemplified here within the context of biomedical researches performed in the Endocrinology and Metabolism Research Institute (EMRI) of Tehran University of Medical Sciences. Two main research aeras have been discussed: the search for new small molecules as therapeutics for diabetes and related metabolic conditions, and diseases related to protein aggregation. Due to their multidisciplinary nature, the majority of these studies have needed the collaboration of different specialties. In both cases, a brief overview of the subject is provided through literature examples, and sequential use of these methods is described.

5-[Aryloxypyridyl (or nitrophenyl)]-4H-1,2,4-triazoles as novel flexible benzodiazepine analogues: Synthesis, receptor binding affinity and lipophilicity-dependent anti-seizure onset of action.

A new series of 5-(2-aryloxy-4-nitrophenyl)-4H-1,2,4-triazoles and 5-(2-aryloxy-3-pyridyl)-4H-1,2,4-triazoles, possessing C-3 thio or alkylthio substituents, was synthesized and evaluated for their benzodiazepine receptor affinity and anti-seizure activity. These analogues revealed similar to significantly superior affinity to GABAA/benzodiazepine receptor complex (IC50 values of 0.04-4.1 nM), relative to diazepam as the reference drug (IC50 value of 2.4 nM). To determine the onset of anti-seizure activity, the time-dependent effectiveness of i.p. administration of compounds on pentylenetetrazole induced seizure threshold was studied and a very good relationship was observed between the lipophilicity (cLogP) and onset of action of studied analogues (r2 = 0.964). The minimum effective dose of the compounds, determined at the time the analogues showed their highest activity, was demonstrated to be 0.025-0.1 mg/kg, relative to diazepam (0.025 mg/kg).

Drug repurposing using computational methods to identify therapeutic options for COVID-19.

PURPOSE: Recently, the world has been dealing with a new type of coronavirus called COVID-19 that in terms of symptoms is similar to the SARS coronavirus. Unfortunately, researchers could not find a registered therapy to treat the infection related to the virus yet. Regarding the fact that drug repurposing is a good strategy for epidemic viral infection, we applied the drug repurposing strategy using virtual screening to identify therapeutic options for COVID-19. For this purpose, five proteins of COVID-19 (3-chymotrypsin-like protease (3CLpro), Papain-Like protease (PLpro), cleavage site, HR1 and RBD in Spike protein) were selected as target proteins for drug repositioning. METHODS: First, five proteins of COVID-19 were built by homology modeling. Then FDA-approved drugs (2471 drugs) were screened against cleavage site and RBD in Spike protein via virtual screening. One hundred and twenty-eight FDA-approved drugs with the most favorable free-binding energy were attached to the cleavage site and RBD in Spike protein. Of these 128 drugs, 18 drugs have either been used currently as antiviral or have been reported to possess antiviral effects. Virtual screening was then performed for the 18 selected drugs with ACE2, 3CLpro and PLpro and HR1 and TMPRSS2. RESULTS: According to the results, glecaprevir, paritaprevir, simeprevir, ledipasvir, glycyrrhizic acid, TMC-310911, and hesperidin showed highly favorably free binding energies with all tested target proteins. CONCLUSION: The above-mentioned drugs can be regarded as candidates to treat COVID-19 infections, but further study on the efficiency of these drugs is also necessary.

Engineering an anti-granulocyte colony stimulating factor receptor nanobody for improved affinity.

AIMS: Granulocyte colony-stimulating factor (G-CSF) is a cytokine that induces proliferation and differentiation of hematopoietic precursor cells and activation of mature neutrophils. G-CSF is overexpressed in several malignant tumors and blocking its binding to the receptor can lead to significant decrease in tumor growth, vascularization and metastasis. Furthermore, targeting G-CSF receptor has shown therapeutic benefit in other diseases such as rheumatoid arthritis, progressive neurodegenerative disorder and uveitis. Camelid single-chain antibodies (nanobodies) have exceptional properties making them appropriate for tumor imaging and therapeutic application. In this study we aim to use the rational design approach to engineer a previously described G-CSF-R targeting nanobody (VHH1), to improve its affinity toward G-CSF-R. MAIN METHODS: We redesigned the complementary determining region 3 (CDR3) domain of the VHH1 nanobody to mimic G-CSF interaction to its receptor and developed five new engineered nanobodies. Binding affinity of the engineered nanobodies was evaluated by ELISA (Enzyme-linked immunosorbent assay) on NFS60 cells. KEY FINDINGS: Enzyme-linked immunosorbent assay (ELISA) confirmed the specificity of the engineered nanobodies and ELISA-based determination of affinity revealed that two of the engineered nanobodies (1c and 5a) bind to G-CSF-R on the surface of NFS60 cells in a dose-dependent manner and with a higher potency compared to the parental nanobody. SIGNIFICANCE: Additional studies are required to better characterize these nanobodies and assess their interaction with G-CSF-R in vitro and in vivo. These newly developed nanobodies could be beneficial in tumor imaging and therapy and make a basis for development of additional engineered nanobodies.

Investigating the role of endogenous opioid system in chloroquine-induced phospholipidosis in rat liver by morphological, biochemical and molecular modelling studies.

Drug-induced phospholipidosis (DIPL) is characterized by phospholipid storage in the lysosomes of affected tissues. Many severe effects and toxicities have been linked to DIPL. The aim of this study was to determine whether the endogenous opioid system is involved in chloroquine-induced phospholipidosis. The effect of naltrexone as an antagonist of opioid receptors in chloroquine-induced phospholipidosis in rat liver was investigated by morphological, biochemical, and molecular modelling studies. Transmission electron microscopy (TEM) showed that morphological characteristic changes of rat liver, including the number of lamellar bodies, grade of vacuolization and cell steatosis, were markedly attenuated in rats treated with naltrexone alone or in combination with chloroquine, in comparison with chloroquine-treated rats. The results of liquid chromatography mass spectrometry (LC/MS) showed that the concentrations of phenylacetylglycine (PAG) and hippuric acid (HA) were significantly decreased and increased, respectively, in target groups. Besides, the concentration ratio of PAG/HA was significantly decreased. Spectrophotometry resulted in a notable decrease in alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities in target groups. The results from the molecular docking and molecular dynamic simulation studies demonstrated clear chloroquine interaction with the active site cavity of the µ opioid receptor. These data suggest that administration of naltrexone alone, or in combination with chloroquine, notably attenuates the side effects of chloroquine-induced phospholipidosis, as well as demonstrating an increased probability of the endogenous opioid system involvement in chloroquine-induced phospholipidosis in rat liver.

Characterization of arginine preventive effect on heat-induced aggregation of insulin.

Aggregation of proteins can affect their efficacy, and is especially important concerning therapeutic proteins such as insulin. Use of additives such as amino acids can counteract this deleterious process. Heat-induced aggregate formation of human insulin was kinetically studied with the use of various concentrations of the protein, at different temperatures, and in the presence of EDTA by UV-visible spectrophotometry. Effect of arginine, lysine, and histidine was then tested on the process at pH 4.8 and 45 °C. Kinetic parameters of the obtained growth curves (parameters t* and t0.5 characterizing the rate of the nucleation stage and the rate of the stage of aggregate growth respectively) were computed in all these conditions, and structure of aggregates was characterized by spectrofluorimetry, and transmission electron microscopy (TEM). Presence of high concentrations of the chelator EDTA increased aggregation. Among used additives, L-arginine (50 mM) most efficiently suppresses the heat-induced amorphous aggregation of insulin, affecting parameters t0.5 and t* presumably by preserving the protein's structure, as observed by the protein intrinsic fluorescence and CD spectra, and smaller formed aggregates in TEM images and dynamic light scattering. Docking experiment and subsequent molecular dynamics simulation indicated possible sites of interaction for arginine with the B-chain of insulin.

Cymene consumption and physical activity effect in Alzheimer's disease model: an in vivo and in vitro study.

PURPOSE: Alzheimer's disease (AD) is one of the most important neurodegenerative diseases and accompanied by the production of free radicals and inflammatory factors. Studies have shown that p-cymene has anti-inflammatory and anti-oxidant effects. Here, the effects of this compound were investigated on a rat model of AD. METHODS: In order to create Alzheimer's rat model, bilateral injection of Amyloid ß1-42 (Aß1-42) into rats hippocampus was performed. Both therapeutic (post-AD induction) and preventive effects of p-cymene consumption with doses of 50 and 100 mg/kg were investigated. In addition, the effects of adding short-term exercise to the process were also observed. In vitro, Aß1-42 peptide was driven toward fibril formation and effect of p-cymene was observed on the resulting fibrils. RESULTS: Learning and memory indices in the AD rats were significantly reduced compared to the Sham group, while p-cymene consumption with both doses, as well as performing exercise counteracted AD consequences. Moreover, increased neurogenesis and reduced amyloid plaques counts were observed in treated rats. In vitro formed fibrils of Aß1-42 were partially disaggregated in the presence of p-cymene. DISCUSSION: p-Cymene could act on this AD model via antioxidant and anti-inflammatory properties as well as direct anti-fibril effect. CONCLUSION: p-cymene can improve AD-related disorders including memory impairment.

Monocyclic phenolic compounds stabilize human insulin and suppress its amorphous aggregation: In vitro and in vivo study.

Insulin is a small protein with 51 residues that mediates glucose uptake, and an interesting model for studying protein misfolding and aggregation. The aggregated forms of insulin undergo loss of activity and can provoke unwanted immune responses. Use of small molecules is considered to be an affordable method to counteract this aggregation process and stabilize insulin. In this study, aggregated forms of human recombinant insulin have been produced following exposure to high temperature. Aggregation process was followed over time by checking absorbance with spectrophotometry in presence and absence of various concentrations of small phenolic compounds including eugenol and epinephrine. Effects of these compounds on the structure and function of incubated insulin were evaluated by spectrofluorimetry, melting temperature (Tm) measurement and insulin tolerance test on Wistar rats. Formation of heat-induced insulin aggregation can be effectively inhibited by 1 mM eugenol and epinephrine and both compounds were found to preserve insulin activity to a considerable extent. In conclusion, simple aromatic compounds could be tailored to act as potent anti-aggregation compounds for insulin.

Inhibition of amyloid fibrillation of apo-carbonic anhydrase by flavonoid compounds.

Flavonoids are polyphenol compounds abundantly found in plants and reported to have an inhibitory effect on amyloid fibrillation. The number and position of hydroxyl groups, as well as the arrangement of flavonoids rings, may influence their inhibitory effects. In this study, we investigate the effect of structural characteristics of flavonoids on amyloid fibril formation. For this purpose, five compounds (i.e., biochanin A, daidzein, quercetin, chrysin and fisetin) were selected that represent a variety in the number and position of their hydroxyl groups. The inhibitory effect of these flavonoids on the amyloid fibril formation of apo-carbonic anhydrase (apo-BCA), as a model protein, was evaluated using thioflavin T and transmission electron microscopy. The results showed that fisetin possessed the most significant inhibitory effect. Interestingly, upon apo-BCA acetylation, none of the tested flavonoids could inhibit the fibrillation process, which indicates that the interactions of these compounds with the amine groups of lysine residues could be somewhat important.