Azaj Ahmed

Purification and biochemical characterization of phytocystatin from Brassica alba

Phytocystatins belong to the family of cysteine proteinases inhibitors. They are ubiquitously found in plants and carry out various significant physiological functions. These plant derived inhibitors are gaining wide consideration as potential candidate in engineering transgenic crops and in drug designing. Hence it is crucial to identify these inhibitors from various plant sources. In the present study a phytocystatin has been isolated and purified by a simple two‐step procedure using ammonium sulfate saturation and gel filtration chromatography on Sephacryl S‐100HR from Brassica alba seeds (yellow mustard seeds).The protein was purified to homogeneity with 60.3% yield and 180‐fold of purification. The molecular mass of the mustard seed cystatin was estimated to be nearly 26 000 Da by sodium dodecyl sulfate polyacrylamide gel electrophoresis as well as by gel filtration chromatography. The stokes radius and diffusion coefficient of the mustard cystatin were found to be 23A° and 9.4 × 10−7 cm2s−1 respectively. The isolated phytocystatin was found to be stable in the pH range of 6–8 and is thermostable up to 60 °C. Kinetic analysis revealed that the phytocystatin exhibited non‐competitive type of inhibition and inhibited papain more efficiently (Ki = 3 × 10−7 M) than ficin (Ki = 6.6 × 10−7 M) and bromelain (Ki = 7.7 × 10−7 M respectively). CD spectral analysis shows that it possesses 17.11% alpha helical content. Copyright

Probing the interaction of anticancer drug temsirolimus with human serum albumin: molecular docking and spectroscopic insight

The binding interaction between temsirolimus, an important antirenal cancer drug, and HSA, an important carrier protein was scrutinized making use of UV and fluorescence spectroscopy. Hyper chromaticity observed in UV spectroscopy in the presence of temsirolimus as compared to free HSA suggests the formation of complex between HSA and temsirolimus. Fluorescence quenching experiments clearly showed quenching in the fluorescence of HSA in the presence of temsirolimus confirming the complex formation and also confirmed that static mode of interaction is operative for this binding process. Binding constant values obtained through UV and fluorescence spectroscopy reveal strong interaction; temsirolimus binds to HSA at 298 K with a binding constant of 2.9 × 104 M−1implying the strength of interaction. The negative Gibbs free energy obtained through Isothermal titration calorimetry as well as quenching experiments suggests that binding process is spontaneous. Molecular docking further provides an insight of various residues that are involved in this binding process; showing the binding energy to be -12.9 kcal/mol. CD spectroscopy was retorted to analyze changes in secondary structure of HSA; increased intensity in presence of temsirolimus showing changes in secondary structure of HSA induced by temsirolimus. This study is of importance as it provides an insight into the binding mechanism of an important antirenal cancer drug with an important carrier protein. Once temsirolimus binds to HSA, it changes conformation of HSA which in turn can alter the functionality of this important carrier protein and this altered functionality of HSA can be highlighted in variety of diseases.

Glyoxal induced structural transition of buffalo kidney cystatin to molten globule and aggregates: Anti‐fibrillation potency of quinic acid

In our study buffalo kidney cystatin (BKC) is transformed from native conformation to amyloid fibrils when incubated with 20 mM glyoxal for a prolonged time period. These amyloid fibrils are at the heart of a number of pathological disorders. In the presence of 10 mM glyoxal, BKC retained native‐like secondary structure, decreased intrinsic and increased ANS fluorescence was observed, characteristics of molten globule state (MG), thus suggesting the occurrence of MG state at this concentration. At 20 mM glyoxal, BKC aggregates were characterized by a further decrease in ANS fluorescence attributable to internalization of hydrophobic clusters owing to protein‐protein interaction. Circular dichroism and FTIR spectroscopy further revealed the existence of β sheet structure and there was an increase in Thioflavin T fluorescence, Rayleigh light scattering, turbidity as well as red shift in congo red absorbance thus confirming the existence of aggregates. We have also studied the anti‐aggregation effect of polyol, quinic acid making use of various above mentioned biophysical assays. Our proposed work strongly favors the formation of BKC aggregates in the presence of glyoxal, which is present in higher amounts in pathological conditions owing to defective glycolysis pathway and also use of polyol as an antifibrillating agent.

Biochemical, immunological and kinetic characterization and partial sequence analysis of a thiol proteinase inhibitor from Bubalus bubalis kidney: An attempt targeting kidney disorders

In the present study a thiol proteinase inhibitor was isolated from buffalo kidney making use of ammonium sulphate precipitation and gel filtration chromatography on Sephacryl S-100HR column. Purified inhibitor is homogeneous as it displayed a single band in gel electrophoresis both under reducing and non-reducing environment and is of 65KDa as revealed by gel filtration and SDS PAGE. Kinetic studies revealed the presence of reversible accompanied with competitive mode of inhibition; showing maximum efficacy against papain (Ki=2.90×10-4). It was maximally active at pH 8.0 and was stable for a period of 30, 60 and 90 days at 37, 4 and -20°C respectively. Immunological studies confirmed its purity of epitopes as a single precipitin line is obtained in immunodiffusion. N-terminal analysis revealed that it shared a good homology with mouse kidney cystatin as well as with Human Cys C and Cys E thereby advocating its use as a model for various human oriented studies which targets how the kidney cystatin level varies in accordance with various drugs that are currently being used as a target for variety of diseases.

Characterizing harmful advanced glycation end-products (AGEs) and ribosylated aggregates of yellow mustard seed phytocystatin: Effects of different monosaccharides.

Advanced glycation end products (AGEs) are at the core of variety of diseases ranging from diabetes to renal failure and hence gaining wide consideration. This study was aimed at characterizing the AGEs of phytocystatin isolated from mustard seeds (YMP) when incubated with different monosaccharides (glucose, ribose and mannose) using fluorescence, ultraviolet, circular dichroism (CD) spectroscopy and microscopy. Ribose was found to be the most potent glycating agent as evident by AGEs specific fluorescence and absorbance. YMP exists as a molten globule like structure on day 24 as depicted by high ANS fluorescence and altered intrinsic fluorescence. Glycated YMP as AGEs and ribose induced aggregates were observed at day 28 and 32 respectively. In our study we have also examined the anti-aggregative potential of polyphenol, resveratrol. Our results suggested the anti-aggregative behavior of resveratrol as it prevented the in vitro aggregation of YMP, although further studies are required to decode the mechanism by which resveratrol prevents the aggregation.

Structural transition of kidney cystatin in dimethylnitrosamine-induced renal cancer in rats: identification as a novel biomarker for kidney cancer and prognosis.

In our study, renal cancer is induced in rats making use of dimethylnitrosamine (DMN). G1 – Group 1 were control rats and G2 – Group 2 rats were given a single intra-peritoneal injection of DMN of 50 mg/kg body weight resulting in 100% incidences of renal tumors after 12 months. SEM and histopathology confirmed the presence of renal cancer in the DMN-treated rats. Making use of ammonium sulfate precipitation and gel filtration chromatography on Sephacryl S-100HR column, a thiol protease inhibitor was isolated from kidney of control rats known as Rat kidney Cystatin (RKC) as well as from kidney of cancerous rat called as Cancerous Rat Kidney Cystatin (CRKC). Both these inhibitors were characterized, and interestingly, it was found that CRKC showed greater anti-papain activity and also it was stable in a broad pH and temperature range thus implying that CRKC is more stable as compared to RKC. UV and fluorescence spectroscopy point out in structural difference between RKC and CRKC which was further confirmed by Circular dichroism (CD) and FTIR spectroscopy. Our study clearly showed that kidney cystatin is structurally modified in the case of renal cancer and performs its role in a more efficacious manner.

Insight into the biochemical, kinetic and spectroscopic characterization of garlic (Allium sativum) phytocystatin: Implication for cardiovascular disease.

Phytocystatins are cysteine proteinase inhibitors present in plants. They play crucial role in maintaining protease-anti protease balance and are involved in various endogenous processes. Thus, they are suitable and convenient targets for genetic engineering which makes their isolation and characterisation from different sources the need of the hour. In the present study a phytocystatin has been isolated from garlic (Allium sativum) by a simple two-step process using ammonium sulphate fractionation and gel filtration chromatography on Sephacryl S-100HR with a fold purification of 152.6 and yield 48.9%. A single band on native gel electrophoresis confirms the homogeneity of the purified inhibitor. The molecular weight of the purified inhibitor was found to be 12.5kDa as determined by SDS-PAGE and gel filtration chromatography. The garlic phytocystatin was found to be stable under broad range of pH (6-8) and temperature (30°C-60°C). Kinetic studies suggests that garlic phytocystatins are reversible and non-competitive inhibitors having highest affinity for papain followed by ficin and bromelain. UV and fluorescence spectroscopy revealed significant conformational change upon garlic phytocystatin-papain complex formation. Secondary structure analysis was performed using CD and FTIR. Garlic phytocystatin possesses 33.9% alpha-helical content as assessed by CD spectroscopy.

Temsirolimus induced structural transition of cancerous renal cystatin to normal form in rats: In vitro mechanistic approach underlying renal cancer prevention

Globally, renal cell carcinomas (RCCs) represent a major portion of patients suffering from cancer. Temsirolimus is an anti-renal cancer drug that has already been approved in poor-risk metastatic RCC (mRCC) patients. In our present study, we have evaluated the in vitro effect of varying concentrations of temsirolimus on cancerous rat kidney cystatin; renal cancer was induced in rats making use of dimethylnitrosamine (DMN). It has already been reported that cancerous rat kidney cystatin performs its activity in an efficacious manner as compared to normal rat kidney cystatin, so here an attempt was made to see the effect of temsirolimus on this increased activity of cystatin in renal cancers. Anti-papain activity assay was utilized to see this effect and it was found that temsirolimus reduces the increased activity of cancerous rat kidney cystatin similar to that of normal rat kidney cystatin. Further, to have an insight into temsirolimus induced structural alterations in cancerous rat kidney cystatin; various spectroscopic assays viz. UV, Fluorescence, Circular dichroism (CD) and FTIR spectroscopy were employed. UV and Fluorescence spectroscopy shows cancerous rat kidney cystatin transformation to normal form in the presence of temsirolimus. FTIR and CD spectroscopy confirmed the complete structural reversion of cancerous rat kidney cystatin to normal form in the presence of 40μM temsirolimus. Thus, it can said that temsirolimus causes renal cystatin to revert to normal form; the increased activity of renal cystatin observed in incidences of renal cancer is restored back to normal thereby halting the progression of renal cancer.

Global transition of human serum albumin to prefibrillar aggregates induced by temsirolimus: Insight into implications of anti-renal cancer drug

In our study, we have characterized the prefibrillar aggregates of human serum albumin (HSA) induced by temsirolimus, anti‐renal cancer drug. Molecular docking was retorted to confirm binding of HSA and temsirolimus. Temsirolimus caused the structural transition of native HSA to non‐native species after prolonged incubation of 20 days. These non‐native species were characterized as prefibrillar aggregates as evident by decreased intrinsic fluorescence and enhanced 8‐anilino‐1‐naphthalene‐sulphonic acid (ANS) fluorescence. Further, enhanced thioflavin T fluorescence and shift in congo red (CR) spectra of temsirolimus‐incubated HSA as compared to native HSA are suggestive of global transition of HSA in presence of temsirolimus towards prefibrillar aggregates. Circular dichroism spectroscopy revealed α to β transition upon prolonged incubation with temsirolimus suggesting the formation of prefibrillar aggregates as aggregates are known to possess high β content. Scanning electron microscopy confirmed these non‐native species to be prefibrillar aggregates evident by observed sheath‐like structures. Comet assay was retorted to confirm genotoxic nature of these prefibrillar aggregates; DNA damage was observed for temsirolimus‐incubated HSA confirming the genotoxic nature of prefibrillar aggregates. These prefibrillar aggregates are observed at heart of many pathological conditions, thus making our study clinically significant.

Investigating the interaction of anticancer drug temsirolimus with human transferrin: Molecular docking and spectroscopic approach

In our present study, binding between an important anti renal cancer drug temsirolimus and human transferrin (hTF) was investigated employing spectroscopic and molecular docking approach. In the presence of temsirolimus, hyper chromaticity is observed in hTF in UV spectroscopy suggestive of complex formation between hTF and temsirolimus. Fluorescence spectroscopy revealed the occurrence of quenching in hTF in the presence of temsirolimus implying complex formation taking place between hTF and temsirolimus. Further, the mode of interaction between hTF and temsirolimus was revealed to be static by fluorescence quenching analysis at 3 different temperatures. Binding constant values obtained employing fluorescence spectroscopy depicts strong interaction between hTF and temsirolimus; temsirolimus binds to hTF at 298 K with a binding constant of .32 × 104 M−1 implying the strength of this interaction. The negative Gibbs free energy obtained through quenching experiments is evident of the fact that the binding is spontaneous. CD spectra of hTF also showed a downward shift in the presence of temsirolimus as compared with free hTF implying complex formation between hTF and temsirolimus. Molecular docking was performed with a view to find out which residues are key players in this interaction. The importance of our study stems from the fact it will provide an insight into binding pattern of commonly administered renal cancer drug with an important protein that plays a pivotal role in many physiological processes.