Purification and Characterization of High Molecular Mass and Low Molecular Mass Cystatin from Goat Brain

Physico-chemical and in-silico analysis of a phytocystatin purified from Brassica juncea cultivar RoAgro 5444

This study describes the isolation and purification of a phytocystatin from seeds of Brassica juncea (Indian mustard; cultivar RoAgro 5444), which is an important oilseed crop both agriculturally and economically. The protein was purified by gel filtration chromatography with 24.3% yield and 204-fold purification, and visualised by 2D gel electrophoresis. The 18.1 kDa mustard cystatin was highly specific for cysteine proteinases. The plant cystatin inhibited cathepsin B, confirming its role in conferring pest resistance. The inhibitor was highly stable over a pH range of 3-10 and retained significant inhibitory potential up to 70 °C. The stoichiometry of its interaction with papain, determined by isothermal calorimetry, suggests a 1:1 complex. Secondary structural elements calculated by far-UV circular dichroism (CD) spectroscopy show an 18.8% α-helical and 21% β-sheet structure. The protein was a non-competitive inhibitor of thiol proteinases. The Stokes radius and frictional co-efficient were used to describe the shape and size of the protein. Homology modelling and docking studies proposed a prototype illustrating the Brassica phytocystatin mediated papain inhibition. Molecular dynamics (MD) study revealed the excellent stability of the papain-phytocystatin complex during a simulation for 100 ns. Detailed results identify the mustard cystatin as an important member of the phytocystatin family.

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)  cm(2) s(-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 (K(i)  = 3 × 10(-7)  M) than ficin (K(i)  = 6.6 × 10(-7)  M) and bromelain (K(i) = 7.7 × 10(-7)  M respectively). CD spectral analysis shows that it possesses 17.11% alpha helical content.

[Effect of curcumin on nitric oxide induced structural and functional modifications of high molecular weight cystatin from the goat brain]

Cystatins are thiol proteinase inhibitors ubiquitously present in the mammalian body. In brain, they prevent unwanted proteolysis and are involved in several neurodegenerative diseases. Under physiological conditions nitric oxide can be found in almost all the tissues, but under pathological conditions NO has damaging effects. Its increased concentration, under various neural diseases leads to cell damage through formation of highly reactive peroxynitrite. Our present study was designed to investigate the protective effect of curcumin against NO induced damage of HM-GBC. NO caused intensive structural and functional damage of HM-GBC, resulting in 89% loss of its antiproteolytic activity after 2 h of incubation. Structural damage occurs in the form of protein degradation. Curcumin significantly protected HM-GBC against this damage. This suggests that curcumin has a significant potential in the treatment of diseases caused by nitrogen free radicals and this potential must be further explored for the development of novel drugs.