Fakhra Amin

Purification and Characterizaion of Buffalo Brain Cystatin

UNLABELLED Cystatins are thiol proteinase inhibitors ubiquitously present in mammalian body and serve various important physiological functions. AIMS To purify and characterize Thiol protease inhibitor from buffalo brain and to compare its properties with respect to tissue and organ difference from other mammalian cystatins. MAIN METHODS Inhibitor has been isolated and purified using alkaline treatment; ammonium sulphate fractionation and gel filtration chromatography on Sephadex G-75 with a % yield of 64.13 and fold purification of 384.72.The inhibitor was studied by U.V and fluorescence spectroscopy. Papain inhibitory activity was measured using casein as substrate. KEY FINDING The molecular weight of the buffalo brain cystatin (BC), determined by gel filtration and SDS PAGE came out to be 43.6 KDa and 44.20 KDa respectively. BC was found to be stable in broad pH and temperature range. The inhibitor was devoid of any sulphydryl group and carbohydrate content. These properties led to conclusion that BC is variant of type-I cystatin. The stokes radius and diffusion coefficient of the inhibitor were found to be 27 A° and 8.1 x 10⁻⁷ cm²/sec respectively, the f/f₀ ratio was 1.12 signifying that purified cystatin is nearly globular in shape. Kinetic data revealed binding stoichiometry of BC with papain as 1:1. The Ki value with papain ficin and bromelain were found to be 1, 1.85 and 2.25 nM respectively suggesting that cystatin has higher affinity with papain as compared to ficin and bromelain. The fluorescence and UV spectra of BC- papain complex showed significant conformational changes indicative of perturbation in the micro environment of aromatic amino acid residues on the formation of complex. SIGNIFICANCE This work proliferates our knowledge about cystatins of the mammalian brain on the basis of their physiochemical properties.

Structural and functional studies on a variant of cystatin purified from brain of Capra hircus.

Cystatins, known for their ubiquitous presence in mammalian system are thiol protease inhibitors serving important physiological functions. Here, we present a variant of cystatin isolated from brain of Capra hircus (goat) which is glycosylated but lacks disulphide bonds. Caprine brain cystatin (CBC) was isolated using alkaline treatment, ammonium sulphate fractionation (40–60%) and gel filtration chromatography on Sephacryl S-100HR column with an overall yield of 26.29% and 322-fold purification. The inhibitor gave a molecular mass of ~44 kDa as determined by SDS-PAGE and gel filtration behaviour. The Stokes radius and diffusion coefficient of CBC were 27.14 Å and 8.18 × 10−7 cm2 s−1, respectively. Kinetic data revealed that CBC inhibited thiol proteases reversibly and competitively, with the highest inhibition towards papain (Ki = 4.10 nM) followed by ficin and bromelain. CBC possessed 34.7% α-helical content as observed by CD spectroscopy. UV, fluorescence, CD and FTIR spectroscopy revealed significant conformational change upon CBC-papain complex formation. Isothermal titration calorimetry (ITC) was used to measure the thermodynamic parameters – ΔH, ΔS, ΔG along with N (binding stoichiometry) for CBC-papain complex formation. Binding stoichiometry (N = .97 ± .07 sites) for the CBC-papain complex indicates that cystatin is surrounded by nearly one papain molecule. Negative ΔH (−5.78 kcal mol−1) and positive ΔS (11.01 cal mol−1 deg−1) values suggest that the interaction between CBC and papain is enthalpically as well as entropically favoured process. The overall negative ΔG (−9.19 kcal mol−1) value implies a spontaneous CBC-papain interaction.

Studies on interaction of buffalo brain cystatin with donepezil: an Alzheimer's drug.

When drugs bind to a protein, the intramolecular structures can be altered, resulting in conformational change of the protein. Donepezil, an Acetyl Cholinesterase inhibitor (AChE), is commonly prescribed to patients with Alzheimers disease (AD) to enhance cholinergic neurotransmission. It is the “first-line” agents in the treatment of Alzheimers disease used to improve cognitive function in the disease. In the present study, a cysteine protease inhibitor (cystatin) has been isolated from buffalo brain using alkaline treatment, 40 to 60% ammonium sulphate fractionation and gel filtration chromatography on Sephadex G-75 with % yield of 64.13 and fold purification of 384.7. The purified inhibitor (Buffalo Brain Cystatin, (BBC)) was eluted as a single papain inhibitory peak which migrated as single band on native PAGE; however, on SDS-PAGE with and without beta mercaptoethanol (βME) BBC gave two bands of M W 31.6 and 12.4 KDa, respectively. The molecular weight determined by gel filtration came out to be 43.6 KDa. The UV spectra of cystatin on interaction with donepezil suggested a conformational change in the protein. The fluorescence spectra of BC-donepezil composite show structural changes indicating 40 nm red shift with significant increase in fluorescence intensity of cystatin in the presence of donepezil representing an unfolding of cystatin on interaction, which is an indication of side effect of donepezil during the use of this drug.

Glycation induced conformational alterations in caprine brain cystatin (CBC) leads to aggregation via passage through a partially folded state

Glycation induced advanced glycation end products (AGEs) of proteins formed as a result of Maillard reaction is currently at the heart of a number of pathological conditions. The formation of chemically stable AGEs can permanently alter protein structure and function; hence can serve as an implication in long term complications. Cystatins with high amyloidogenic inclination are implicated in various diseases including cancer and neurodegenerative conditions. The aggregates of cystatin purified from caprine brain have been studied on addition of glucose and ribose using UV absorption, fluorescence emission, circular dichroism (CD) spectroscopy and transmission electron microscopy (TEM). In the present study AGEs have been monitored and characterized. CBC was incubated for varying time intervals up to 41days in the presence of 17 and 100mM each of glucose and ribose. Ribose at both the concentrations was found to be more potent glycating agent as compared to glucose at these concentrations which is evident from UV and fluorescence spectroscopic studies. Altered intrinsic and high ANS fluorescence for 100mM and 17mM sugar concentrations respectively, suggested the existence of molten globule state of CBC. Glycated CBC as AGEs and aggregates were observed on day 27 and 41 respectively. Formation of AGEs was confirmed by employing AGEs specific fluorescence studies. CBC aggregates confirmed the presence of β-sheet structure as shown by far-UV CD, dye binding assay and transmission electron microscopy (TEM). Current study is of immense importance as cystatin is a potential candidate of amyloidogenic tendency and a potent endogenous regulator of thiol proteases; hence serves to be an attractive model to study amyloidogenesis of brain cysteine protease inhibitor.

Spectroscopic Studies on free radical coalescing antioxidants and Brain protein cystatin

Abstract Cystatins are the inhibitors of thiol proteinases and are ubiquitously present in mammalian system. In brain, they put off unwanted proteolysis and are also involved in several neurodegenerative diseases. In the present study, it was demonstrated that photo-activated HOCl-induced modifications in brain cystatin leading to its inactivation and degradation due to hydroxyl radicals. It has been shown that oxidation of cystatin by ROS in vivo leads to oxidative modification which may direct the damage of this significant protein, as it is so well pronounced in vitro. The interplay between free radicals, antioxidants and co-factors is important in maintaining health, aging and age-related diseases. Body’s endogenous antioxidant systems stabilize free radical-induced oxidative stress by the ingestion of exogenous antioxidants. If the generation of free radicals goes beyond the protective effect of antioxidants, this can cause oxidative damage which accumulates during the life cycle and has been implicated in aging and age-related diseases such as cardiovascular disease, cancer, neurodegenerative disorders and other chronic conditions. Activation of neutrophils in certain diseases (e.g., inflammatory conditions and atherosclerosis) results in the production of highly reactive species, such as OH• and the release of the enzyme myeloperoxidase. Stimulated monocytes and neutrophils generate hypochlorite (HOCl) via the release of the enzyme myeloperoxidase and hydrogen peroxide. Hypochlorous acid (HOCl) is a potent oxidant formed by myeloperoxidase that causes aggregation of many proteins and damage of proteins by reaction with amino-acid side-chains or backbone cleavage. Communicated by Ramaswamy H. Sarma

Damage of cystatin due to ROS-generation and radical-scavenging activity of antioxidants and associated compounds

Cystatins are thiol proteinase inhibitors present ubiquitously in mammalian system. They prevent unwanted proteolysis and are involved in several neurodegenerative diseases. Hydrogen peroxide, hydroxyl radical and superoxide radical were produced during the autoxidation of various cytotoxic agents namely 6-hydroxydopamine, 6-aminodopamine, 6,7-dihydroxytryptamine, and dialuric acid. Reactive oxygen species (ROS) such as singlet oxygen [O2-] and hydroxyl radicals result in nonspecific reactivity, thus involved in several pathological conditions such as inflammation and reperfusion injury leading to damage of different biological molecules due to the production of enzyme myeloperoxidase because of activation of neutrophils in these diseases. As Myeloperoxidase [MPO] is released extracellularly by activated monocytes and is highly basic protein that damages the localized sites. The onset and progression of several diseases is a complex process in which oxidation is believed to play significant role. Oxidized lipids and proteins that are detected in early, intermediate and advanced stage of human neurodegenerative diseases (plaques) have revealed considerably elevated levels of reactive oxygen species showing their involvement in brain diseases. In the present study, it has been demonstrated that H2O2 induced modifications in brain cystatin leads to its inactivation and degradation. It was also found that the damage from the oxidants occurred mainly because of the (ROS) hydroxyl radicals [OH] produced by H2O2 which in turn changes the conformation of the Cystatin, a major factor for the damage of this significant protein. It is one of the cause of protease-antiprotease imbalance in mammals leading to progression of several diseases.

Effect of Amitriptyline an Antidepressant Drug on Structural and Functional Properties of Brain Cystatin

Cystatins are the thiol proteinases inhibitors of prime physiologic importance. They are ubiquitously present in mammalian body. They prevent unwanted proteolysis and play important role in several diseases. Regulation of cysteine proteinases and their inhibitors are of utmost importance in diseases like Alzheimer, amlyoid angiopathy and other neurodegenerative disease. Proteinase anti-proteinase imbalance accelerates disease progression. Amitriptylin an antidepressant helps to relieve depression and pain. It is often used to manage nerve pain resulting from cancer treatment. Such injury to nerves causes a burning, tingling sensation. This medication, usually given at bedtime, helps patients to sleep better In this paper interaction of brain cystatin (BC) with Amytriptyline (AMY) has been studied by UV absorption and fluorescence spectroscopy. In the present study, the effect of drug has been studied to explore AMY induced changes in functional and structural integrity of the cystatin. The fluorescence quenching data is indicative of complex formation between the protein and drug which confirmed the binding of Amytriptyline with brain cystatin. Stern-Volmer analysis of Amytriptyline binding with brain cystatin indicates the presence of static component in the quenching mechanism. The thermodynamic parameters ΔG° (Free energy change) -36.966 KJ/mol indicated that both hydrogen bonds and hydrophobic interactions played a major role in the binding of AMY with BC. Binding investigations give in this work, gives significant information about the conformational changes in cystatin due interaction with the drug.

Antidepressant Fluoxetine Modulates the In Vitro Inhibitory Activity of Buffalo Brain Cystatin: A Thermodynamic Study Using UV and Fluorescence Techniques

Cystatins constitute a superfamily of homologous proteins. The major role of cystatins is to regulate the unwanted proteolysis and to protect the organism against endogenous proteases released from lysosomes, invading microorganisms and parasites that use cysteine proteases to enter the body. Imbalance in regulation of proteolytic activity may lead to a wide range of human diseases. An enormous progress has been made in understanding of protein degradation process under normal and pathological conditions; infact proteases are now clearly viewed as important drug targets. Fluoxetine a selective serotonin reuptake inhibitor (SSRI) is an antidepressant. It is used to treat major depressive disorders. In the present study binding of fluoxetine to cystatin was studied by UV and fluorescence quenching technique. Intrinsic fluorescence of fluoxetine complexed with purified buffalo brain cystatin (BC) was measured by selectively exciting the tryptophan residues. Gradual quenching was observed on complex formation. When cystatin was added to fluoxetine solutions at a molar ratio of 1 : 0.5, it not only quenched more than half of its fluorescence but also reduced the activity of cystatin. Stern-Volmer plots obtained from experiments carried out at 25°C showed the quenching of fluorescence to be a collisional phenomenon. Our results suggest the prime binding site for fluoxetine on BC to be at or near tryptophan residues. Fluoxetine quenched the fluorescence by a static process, which specifically indicates the formation of a complex.