Modification of chickpea cystatin by reactive dicarbonyl species: Glycation, oxidation and aggregation.

Reactive dicarbonyl species such as methylglyoxal (MGO) and glyoxal (GO) have recently received extensive attention due to their high reactivity and ability to modify biological substances such as proteins, phospholipids, and DNA. In case of proteins these reactive species mainly react with lysine and arginine residues to form AGEs, oxidative products, and aggregates. Chickpea cystatin (CPC) was incubated with varying concentrations of glyoxal and methylglyoxal which caused, along with altered secondary and tertiary structures, glycation, functional inactivation, altered redox state, cross-linking and high-molecular-mass aggregation. All these processes were examined and characterized by UV-Vis, fluorescence, and CD spectroscopies. Further characterization of CPC modified by reactive dicarbonyls was done by polyacrylamide gel electrophoresis which also showed alterations in the CPC molecules. Thus, in addition to describing the effects of GO and MGO on structure, conformation and function of CPC, this study also shows the relatively superior modifying effect of methylglyoxal for CPC in terms of glycation, oxidation and aggregation. This model system could shed some more light on the role of the reactive dicarbonyls in the specific alterations of proteins with different biological consequences having implications to ageing and disease such as diabetes.

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 ß-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.

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.

Benzo(a)pyrene induced structural and functional modifications in lung cystatin.

Cystatins are thiol proteinase inhibitors ubiquitously present in the mammalian body. They serve a protective function to regulate the activities of endogenous proteinases, which may cause uncontrolled proteolysis and damage. In the present study, the effect of benzo(a)pyrene [BaP] on lung cystatin was studied to explore the hazardous effects of environmental pollutant on structural and functional integrity of the protein. The basic binding interaction was studied by UV-absorption, FT-IR, and fluorescence spectroscopy. The enhancement of total protein fluorescence with a red shift of 5 nm suggests structural scratch of lung cystatin by benzo(a)pyrene. Further, ANS binding studies reaffirm the unfolding of the thiol protease inhibitor (GLC-I) after treating with benzo(a)pyrene. The results of FT-IR spectroscopy reflect perturbation of the secondary conformation (alpha-helix to ß-sheet) in goat lung cystatin on interaction with BaP. Finally, functional inactivation of cystatin on association with BaP was checked by its papain inhibitory activity. Benzo(a)pyrene (10 µM) caused complete inactivation of goat lung cystatin. Benzo(a)pyrene-induced loss of structure and function in the thiol protease inhibitor could provide a caution for lung injury caused by the pollutants and smokers.