Trifluoroethanol and acetonitrile induced formation of the molten globule states and aggregates of cellulase

Glyoxal Induced Transition of Transferrin to Aggregates: Spectroscopic, Microscopic and Molecular Docking Insight

BACKGROUND & OBJECTIVE

The present study was aimed at characterizing the conformational alterations induced in human transferrin, the iron regulatory protein by glyoxal. Since protein aggregation is at the core of many disorders, thus interest in this domain has increased significantly during the past years.

METHODS

In our present study, the effect of glyoxal was monitored on human transferrin using multispectroscopic and multi-microscopic studies.

RESULTS

Intrinsic fluorescence spectroscopy suggested changes in native conformation of human transferrin evident by decreased fluorescence and blue shift in the presence of glyoxal. Further, extrinsic fluorescence was retorted and the results showed the formation of aggregates; apparent by increased Congo red (CR) absorbance, Thioflavin T (ThT) and ANS fluorescence and TEM of human transferrin in the presence of glyoxal. Molecular docking was also employed to see which residues are at core of human transferrin and glyoxal interaction. Reactive oxygen species (ROS) generation assays revealed enhanced ROS levels by human transferrin after treatment with glyoxal.

CONCLUSION

Thus, our study proposes that glyoxal induces the formation of aggregates in human transferrin. These aggregates further generate ROS which are key players in the complications associated with diabetes mellitus, giving our study clinical perspective.

A biophysical insight into the formation of aggregates upon trifluoroethanol induced structural and conformational changes in garlic cystatin

Intrinsic and extrinsic factors are responsible for the transition of soluble proteins into aggregated form. Trifluoroethanol is among such potent extrinsic factor which facilitates the formation of aggregated structure. It disrupts the interactive forces and destabilizes the native structure of the protein. The present study investigates the effect of trifluoroethanol (TFE) on garlic cystatin. Garlic cystatin was incubated with increasing concentration of TFE (0-90% v/v) for 4 h. Incubation of GPC with TFE induces structural changes thereby resulting in the formation of aggregates. Inactivation of garlic phytocystatin was confirmed by cysteine proteinase inhibitory activity. Garlic cystatin at 30% TFE exhibits native-like secondary structure and high ANS fluorescence, thus suggesting the presence of molten globule state. Circular dichroism and FTIR confirmed the transition of the native alpha-helical structure of garlic cystatin to the beta-sheet structure at 60% TFE. Furthermore, increased ThT fluorescence and redshift in Congo red absorbance assay confirmed the presence of aggregates. Rayleigh and turbidity assay was also performed to validate the aggregation results. Scanning electron microscopy was followed to analyze the morphological changes which confirm the presence of sheath-like structure at 60% TFE. The study sheds light on the conformational behavior of a plant protein when kept under stress condition induced by an extrinsic factor.

Aloe emodin, an anthroquinone from Aloe vera acts as an anti aggregatory agent to the thermally aggregated hemoglobin

Aggregation of proteins is a physiological process which contributes to the pathophysiology of several maladies including diabetes mellitus, Huntington's and Alzheimer's disease. In this study we have reported that aloe emodin (AE), an anthroquinone, which is one of the active components of the Aloe vera plant, acts as an inhibitor of hemoglobin (Hb) aggregation. Hb was thermally aggregated at 60°C for four days as evident by increased thioflavin T and ANS fluorescence, shifted congo red absorbance, appearance of β sheet structure, increase in turbidity and presence of oligomeric aggregates. Increasing concentration of AE partially reverses the aggregation of the model heme protein (hemoglobin). The maximum effect of AE was observed at 100μM followed by saturation at 125μM. The results were confirmed by UV-visible spectrometry, intrinsic fluorescence, ThT, ANS, congo red assay as well as transmission electron microscopy (TEM). These results were also supported by fourier transform infrared spectroscopy (FTIR) and circular dichroism (CD) which shows the disappearance of β sheet structure and appearance of α helices. This study will serve as baseline for translatory research and the development of AE based therapeutics for diseases attributed to protein aggregation.

Neo-Epitopes Generated on Hydroxyl Radical Modified GlycatedIgG Have Role in Immunopathology of Diabetes Type 2

Glycoxidation plays a crucial role in diabetes and its associated complications. Among the glycoxidation agents, methylglyoxal (MG) is known to have very highglycationpotential witha concomitant generation of reactive oxygen species (ROS) during its synthesis and degradation. The presentstudy probes the MG and ROSinduced structural damage to immunoglobulin G (IgG) and alterations in its immunogenicity in diabetes type 2 patients (T2DM). Human IgG was first glycated with MG followed by hydroxyl radical (OH•) modification. Glycoxidation mediated effects on IgG were evaluated by various physicochemical techniques likeultraviolet (UV) and fluorescence spectroscopy, 8-anilinonaphthalene-1-sulfonic acid (ANS) binding studies, carbonyl andfree sulfhydryl groups assay, matrix assisted laser desorption ionization mass spectrometry-time of flight (MALDI-TOF), red blood cell (RBC) haemolysis assay, Congored (CR) staining analysis and scanning electron microscopy (SEM). The results revealed hyperchromicityin UV, advanced glycation end product (AGE)specific and ANS fluorescence, quenching in tyrosine and tryptophan fluorescence intensity,enhanced carbonyl content,reduction in free sulfhydryl groups,pronounced shift in m/z value of IgGand decrease in antioxidant activity in RBC induced haemolysis assayupon glycoxidation. SEM and CRstaining assay showed highly altered surface morphology in glycoxidised sample as compared to the native. Enzyme linked immunosorbent assay (ELISA) and band shift assay were performed to assess the changes in immunogenicity of IgG upon glyoxidation and its role in T2DM. The serum antibodies derived from T2DM patients demonstrated strong affinity towards OH• treated MG glycatedIgG (OH•-MG-IgG) when compared to native IgG (N-IgG) or IgGs treated with MG alone (MG-IgG) or OH• alone (OH•-IgG). This study shows the cumulating effect of OH• on the glycation potential of MG. The results point towards the modification of IgG in diabetes patients under the effect of glycoxidative stress, leading to the generation of neo-epitopes on theIgG molecule and rendering it immunogenic.

Aggregation as a consequence of glycation: insight into the pathogenesis of arthritis

Advanced glycation end products (AGEs) as a result of Maillard reaction are currently at the heart of the pathogenesis of several diseases and hence are the objective of numerous investigations. Glycation of proteins has been an implication in long-term complications. Collagen is the most abundant protein in the human body. The purpose of this study was to monitor and characterize the oligomeric aggregates and AGEs of human collagen on addition of glyoxal using ultraviolet, fluorescence, circular dichroism (CD) spectroscopy, docking studies, ITC, and microscopy. Collagen was incubated for varying time periods up to 21 days with three different concentrations (5, 20, and 40 mM) of glyoxal. Collagen exists as molten globule at day 6, evident from native-like secondary structure, altered tryptophan, and high ANS fluorescence due to surface-exposed hydrophobic residues. Glycated collagen as AGEs and aggregates was observed at day 18 and 21, respectively. Formation of AGE and aggregates were confirmed by UV and fluorescence spectroscopy. The obtained AGEs were characterized with respect to the extent of side chain modifications (lysine and arginine) forming the Schiff base, the carboxymethyl lysine, and carbonyl content. Non-tryptophan fluorescence for AGEs was also monitored as the emission peak at 400 and 440 nm, respectively. SEM and TEM confirmed the oligomeric nature of aggregates. Glyoxal at 40 mM shows maximum alterations in protein structure followed by 20 and 5 mM concentration. In the present paper, we propose that a high concentration of glyoxal for a prolonged time results in the formation of harmful aggregates and AGEs.

Insight into the co-solvent induced conformational changes and aggregation of bovine β-lactoglobulin

Many proteins form ordered irreversible aggregates called amyloid fibrils which are responsible for several neurodegenerative diseases. β-lactoglobulin (β-lg), an important globular milk protein, self-assembles to form amyloid-like fibrils on heating at low pH. The present study investigated the effects of two commonly used organic solvents acetonitrile (MeCN) and antimicrobial preservative benzyl alcohol (BA) on the conformation and self-assembly of β-lg at ambient condition. Both MeCN and BA induced a concentration-dependent conformational change showing exposure of hydrophobic patches, loss of tertiary structure and higher α-helical structure at moderate concentrations. In the presence of 50-80% (v/v) MeCN and 1.5-3% (v/v) BA further structural transitions from α-helical to non-native β-sheet structure were observed with a molten globule-like intermediate at 70% MeCN. These non-native β-sheet structures have high tendency to form aggregates. The formation of β-lg self-assembly was confirmed by Thioflavin T studies, Congo red assay, Rayleigh scattering and dynamic light scattering analysis. Transmission electron microscopy studies showed amyloid fibril formation in both MeCN and BA. Our results showed that BA enhances the unfolding and self-assembly of β-lg at much lower concentration than MeCN. Thus solvent composition forces the protein to achieve the non-native structures which are responsible for protein aggregation.

Anesthetic 2,2,2-trifluoroethanol induces amyloidogenesis and cytotoxicity in human serum albumin

Trifluoroethanol (TFE) mimics the membrane environments as it simulates the hydrophobic environment and better stabilizes the secondary structures in peptides owing to its hydrophobicity and hydrogen bond-forming properties. Its dielectric constant approximates that of the interior of proteins and is one-third of that of water. Human serum albumin (HSA) is a biological transporter. The effect of TFE on HSA gives the clue about the conformational changes taking place in HSA on transport of ligands across the biological membranes. At 25% (v/v) and 60% (v/v) TFE, HSA exhibits non-native β-sheet, altered tryptophan fluorescence, exposed hydrophobic clusters, increased thioflavin T fluorescence and prominent red shifted Congo red absorbance, and large hydrodynamic radii suggesting the aggregate formation. Isothermal titration calorimetric results indicate weak binding of TFE and HSA. This suggests that solvent-mediated effects dominate the interaction of TFE and HSA. TEM confirmed prefibrillar at 25% (v/v) and fibrillar aggregates at 60% (v/v) TFE. Comet assay of prefibrillar aggregates showed DNA damage causing cell necrosis hence confirming cytotoxic nature. On increasing concentration of TFE to 80% (v/v), HSA showed retention of native-like secondary structure, increased Trp and ANS fluorescence, a transition from β-sheet to α-helix. Thus, TFE at high concentration possess anti- aggregating potency.

Structural characterization of MG and pre-MG states of proteins by MD simulations, NMR, and other techniques

Almost all proteins fold via a number of partially structured intermediates such as molten globule (MG) and pre-molten globule states. Understanding the structure of these intermediates at atomic level is often a challenge, as these states are observed under extreme conditions of pH, temperature, and chemical denaturants. Furthermore, several other processes such as chemical modification, site-directed mutagenesis (or point mutation), and cleavage of covalent bond of natural proteins often lead to MG like partially unfolded conformation. However, the dynamic nature of proteins in these states makes them unsuitable for most structure determination at atomic level. Intermediate states studied so far have been characterized mostly by circular dichroism, fluorescence, viscosity, dynamic light scattering measurements, dye binding, infrared techniques, molecular dynamics simulations, etc. There is a limited amount of structural data available on these intermediate states by nuclear magnetic resonance (NMR) and hence there is a need to characterize these states at the molecular level. In this review, we present characterization of equilibrium intermediates by biophysical techniques with special reference to NMR.

Conformational behaviour and aggregation of chickpea cystatin in trifluoroethanol: effects of epicatechin and tannic acid

Conformational alterations and aggregates of chickpea cystatin (CPC) were investigated upon sequential addition of trifluoroethanol (TFE) over a range of 0-70% v/v. CPC on 30% and 40% v/v TFE addition exhibited non-native β-sheet, altered intrinsic fluorescence, increased thioflavin T fluorescence, prominent red shifted shoulder peak in Congo red absorbance, and enhanced turbidity as well as Rayleigh scattering, suggesting the aggregate formation. TEM results confirmed the formation of fibrillar aggregates at 30% and 40% v/v TFE. On increasing concentration of TFE to 70% v/v, CPC showed retention of native-like secondary structure, increased intrinsic and ANS fluorescence. Thus our results show that favourable condition for fibrillation of CPC is in the range of 30-40% TFE. Moreover, anti-aggregational effects of polyphenols, epicatechin (EC) and tannic acid (TA) were analysed using ThT binding assay and other biophysical assays. EC and TA produced a concentration dependent decline in ThT fluorescence suggesting inhibition of the fibril formation. Furthermore, TA in comparison to EC, served as a more effective inhibitor against amyloid fibril formation of CPC. This work supports the universality of the amyloid-like aggregation not restricted to some special categories of protein and the fact that this aggregation can be prevented.

An insight into the biophysical characterization of insoluble collagen aggregates: implication for arthritis

Misfolding and aggregation of proteins is involved in some of the most prevalent neurodegenerative disorders. The importance of collagen stems from the fact that it is one of the dominant component used for tissue engineering and drug delivery applications and is a major component of skin, tendon, bone and other connective tissues. A systematic investigation on the conformation of collagen at various concentrations of glyoxal is studied by various biophysical techniques such as Trp fluorescence, ANS binding, Circular dichroism (CD), ATR-FTIR, Congo red (CR) assay, Rayleigh light scattering and Turbidity measurements. At 60% (v/v) glyoxal, collagen retains native-like secondary structure, altered Trp environment and high ANS fluorescence, characteristic of molten globule (MG) state. At 80% (v/v) glyoxal, insoluble collagen aggregates are detected as confirmed by decrease in Trp and ANS fluorescence, increase in non-native β sheet structure as evident from far-UV CD and FTIR spectra, increase in Thioflavin T fluorescence, Rayleigh light scattering, Turbidity measurements, as well as red shift in CR absorbance.

Molten globule of hemoglobin proceeds into aggregates and advanced glycated end products

Conformational alterations of bovine hemoglobin (Hb) upon sequential addition of glyoxal over a range of 0–90% v/v were investigated. At 20% v/v glyoxal, molten globule (MG) state of Hb was observed by altered tryptophan fluorescence, high ANS binding, existence of intact heme, native-like secondary structure as depicted by far-UV circular dichroism (CD) and ATR-FTIR spectra as well as loss in tertiary structure as confirmed by near-UV CD spectra. In addition, size exclusion chromatography analysis depicted that MG state at 20% v/v glyoxal corresponded to expanded pre-dissociated dimers. Aggregates of Hb were detected at 70% v/v glyoxal. These aggregates of Hb had altered tryptophan environment, low ANS binding, exposed heme, increased β-sheet secondary structure, loss in tertiary structure, enhanced thioflavin T (ThT) fluorescence and red shifted Congo Red (CR) absorbance. On incubating Hb with 30% v/v glyoxal for 0–20 days, advanced glycation end products (AGEs) were detected on day 20. These AGEs were characterised by enhanced tryptophan fluorescence at 450 nm, exposure of heme, increase in intermolecular β-sheets, enhanced ThT fluorescence and red shift in CR absorbance. Comet assay revealed aggregates and AGEs to be genotoxic in nature. Scanning electron microscopy confirmed the amorphous structure of aggregates and branched fibrils of AGEs. The transformation of α-helix to β-sheet usually alters the normal protein to amyloidogenic resulting in a variety of protein conformational disorders such as diabetes, prion and Huntington's.

Detection and analysis of protofibrils and fibrils of hemoglobin: implications for the pathogenesis and cure of heme loss related maladies

TFE induces structural alterations of proteins similar to the lipid environment of biological membranes, implicating these studies worthy of analyzing protein conformation in membranes such as red blood cells (RBCs). Heme loss occurs on rupturing of RBCs as found in diseases namely haemophilia, haemolytic anaemia, diabetes mellitus. TFE can be implied in discovering therapeutic targets, as it mimics the biological membrane environment. A global transition of hemoglobin (Hb) in presence of TFE was studied by using multi-methodological approach. The presence of partially folded state of Hb at 15% v/v TFE was confirmed by altered tryptophan environment, and retention of native-like secondary and tertiary structure. Molten globule state was observed at 20% v/v TFE as detected by increase tryptophan and high ANS fluorescence, slight alterations in Soret band relative to native. TFE on increasing concentration induced protofibrils at 25% v/v and fibrils at 45% v/v as depicted by altered tryptophan environment, heme loss, increase in non-native β-sheet secondary and tertiary structure, large hydrodynamic radii of heme-protein, high ANS, thioflavin T fluorescence and shift in Congo Red absorbance. Comet assay showed that protofibrils are cytotoxic to lymphocytes. SEM and XRD confirmed these aggregates to be fibrillar in nature.