Solution structure of a phytocystatin from Ananas comosus and its molecular interaction with papain

A novel cysteine proteinase inhibitor from seeds of Enterolobium contortisiliquum and its effect on Callosobruchus maculatus larvae

This study focused on the characterization of a novel cysteine proteinase inhibitor from Enterolobium contortisiliquum seeds targeting the inhibition of the growth of Callosobruchus maculatus larvae, an important cosmopolitan pest of the cowpea Vigna unguiculata during storage. The inhibitor was isolated by ion-exchange besides of size exclusion chromatography. EcCI molecular mass is 19,757 Da, composed of two polypeptide chains. It strongly inhibits papain (Kiapp 0.036 nM) and proteinases from the midguts of C. maculatus (80 μg mL-1, 60% inhibition). The inhibitory activity is reduced by 40% after a heat treatment at 100 °C for 2 h. The protein displayed noxious activity at 0.5% and 1% (w/w) when incorporated in artificial seeds, reducing larval mass in 87% and 92%, respectively. Treatment of C. maculatus larvae with conjugated EcCI-FIT and subsequent biodistribution resulted in high fluorescence intensity in midguts and markedly low intensity in malpighian tubules and fat body. Small amounts of labeled proteins were detected in larvae feces. The detection of high fluorescence in larvae midguts and low fluorescence in their feces indicate the retention of the FITC conjugated EcCI inhibitor in larvae midguts. These results demonstrate the potential of the natural protein from E. contortisiliquum to inhibit the development of C. maculatus.

Protein aggregation as a consequence of non-enzymatic glycation: Therapeutic intervention using aspartic acid and arginine

Non-enzymatic glycation tempted AGEs of proteins are currently at the heart of a number of pathological conditions. Production of chemically stable AGEs can permanently alter the protein structure and function, concomitantly leading to dilapidated situations. Keeping in perspective, present study aims to report the glycation induced structural and functional modification of a cystatin type isolated from rai mustard seeds, using RSC-glucose and RSC-ribose as model system. Among the sugars studied, ribose was found to be most potent glycating agent as evident from different biophysical assays. During the course of incubation, RSC was observed to pass through a series of structural intermediates as revealed by circular dichroism, altered intrinsic fluorescence and high ANS binding. RSC incubation with ribose post day 36 revealed the possible buildup of β structures as observed in CD spectral analysis, hinting towards the generation of aggregated structures in RSC. High thioflavin T fluorescence and increased Congo red absorbance together with enhanced turbidity of the modified form confirmed the aggregation of RSC. The study further revealed anti-glycation and anti-aggregation potential of amino acids; aspartic acid and arginine as they prevented and/or slowed down the process of AGEs and β structure buildup in a concentration dependent manner with arginine proving to be the most effective one.

A new Piper nigrum cysteine proteinase inhibitor, PnCPI, with antifungal activity: molecular cloning, recombinant expression, functional analyses and molecular modeling

A new Piper nigrum cysteine proteinase inhibitor, PnCPI, belonging to group I of phytocystatins, with inhibitory activity against papain and growth of Fusarium solani f. sp. piperis, was isolated and characterized. Previous studies (de Souza et al. 2011) have identified a partial cDNA sequence of putative cysteine proteinase inhibitor differentially expressed in roots of black pepper (P. nigrum L.) infected by F. solani f. sp. piperis. Here, we aimed to isolate the full-length cDNA and genomic sequences of the P. nigrum cysteine proteinase inhibitor gene, named PnCPI. Sequence analyses showed that the PnCPI gene encodes a deduced protein of 108 amino acid residues with a predicted molecular mass of 12.3 kDa and isoelectric point of 6.51. Besides the LARFAV-like sequence, common to all phytocystatins, PnCPI contains three conserved motifs of the superfamily cystatin: a glycine residue at the N-terminal region, the QxVxG reactive site more centrally positioned, and one tryptophan in the C-terminal region. PnCPI, belonging to group I of phytocystatins, showed high identity with cystatins isolated from several plant species. Sequence analyses also revealed no putative signal peptide at the N-terminal of PnCPI, as well as no introns within the genomic sequence corresponding to the PnCPI coding region. Molecular modeling showed the ability of PnCPI to interact with papain, while its inhibitory activity against this protease was confirmed after heterologous expression in Escherichia coli. The effects of heat treatments on the inhibitory activity of recombinant PnCPI, rPnCPI, were evaluated. In addition, rPnCPI exhibited in vitro activity against F. solani f. sp. piperis, revealing a new cystatin with the potential antifungal application. The identification of PnCPI as a functional cystatin able to inhibit the in vitro growth of F. solani f. sp. piperis indicates other factors contributing to in vivo susceptibility of black pepper to root rot disease.

Insight into the biochemical characterization of phytocystatin from Glycine max and its interaction with Cd+2 and Ni+2

Phytocystatins are cysteine proteinase inhibitors ubiquitously present in plants and animals. They are known to carry out various significant physiological functions and also maintain the balance of protease-antiprotease activity. In the present disquisition, a phytocystatin after preliminary treatment has been isolated and purified to homogeneity from soybean (Glycine max) by a simple two-step stratagem using ammonium sulfate fractionation and gel filtration chromatography performed on Sephacryl S-100-HR. Soybean phytocystatin (SBPC) was purified with a fold purification of 635 and percent yield of 77.6%. A single band was observed on native gel electrophoresis confirming the homogeneity of the purified SBPC. The molecular weight of SBPC was found to be 19.05 kDa as determined by SDS-PAGE. The SBPC was found to be devoid of carbohydrate moieties and sulfhydryl group content. The binding stoichiometry of SBPC-papain interaction was determined by isothermal calorimetry suggesting 1:1 complex, and the value of binding constant (K) was found to be 2.78 × 105  M-1 The affinity of binding (Kd ) value obtained through ITC was 3.59 × 10-6  M. The purified SBPC was found to be stable in the pH range of 3 to 7 and is thermostable up to 50°C. The UV-visible and fluorescence studies showed significant changes in the conformation upon the formation of the SBPC-papain complex. Furthermore, fluorescence spectroscopy, ANS binding, and caseinolytic activity assay were conducted out to explore the effect of metal ions on SBPC which showed that there was a loss in the inhibitory activity along with conformational changes of SBPC upon complex formation with Cd+2 and Ni+2 .

A new mixed inhibitor of adenosine deaminase produced by endophytic Cochliobolus sp. from medicinal plant seeds

Medicinal plants have been studied for potential endophytic interactions and numerous studies have provided evidence that seeds harbor diverse microbial communities, not only on their surfaces but also within the embryo. Adenosine deaminase (ADA) is known as a potential therapeutic target for the treatment of lymphoproliferative disorders and cancer. Therefore, in this study, 20 types of medicinal plant seeds were used to screen endophytic fungi with tissue homogenate and streak. In addition, 128 morphologically distinct endophyte strains were isolated and their ADA inhibitory activity determined by a spectrophotometric assay. The strain with the highest inhibitory activity was identified as Cochliobolus sp. Seven compounds were isolated from the strain using a chromatography method. Compound 3 showed the highest ADA inhibitory activity and was identified as 5-hydroxy-2-hydroxymethyl-4H-pyran-4-one, based on the results of 1H and 13C NMR spectroscopy. The results of molecular docking suggested that compound 3 binds to the active site and the nonspecific binding site of the ADA. Furthermore, we found that compound 3 is a mixed ADA inhibitor. These results indicate that endophytic strains are a promising source of ADA inhibitors and that compound 3 may be a superior source for use in the preparation of biologically active ADA inhibitor compounds used to treat cancer.

Recombinant cystatins in plants

Dozens of studies have assessed the practical value of plant cystatins as ectopic inhibitors of Cys proteases in biological systems. The potential of these proteins in crop protection to control herbivorous pests and pathogens has been documented extensively over the past 25 years. Their usefulness to regulate endogenous Cys proteases in planta has also been considered recently, notably to implement novel traits of agronomic relevance in crops or to generate protease activity-depleted environments in plants or plant cells used as bioreactors for recombinant proteins. After a brief update on the basic structural characteristics of plant cystatins, we summarize recent advances on the use of these proteins in plant biotechnology. Attention is also paid to the molecular improvement of their structural properties for the improvement of their protease inhibitory effects or the fine-tuning of their biological target range.

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.

Identification of a type II cystatin in Fragaria chiloensis: A proteinase inhibitor differentially regulated during achene development and in response to biotic stress-related stimuli

The equilibrium between protein synthesis and degradation is key to maintaining efficiency in different physiological processes. The proteinase inhibitor cystatin regulates protease activities in different developmental and physiological contexts. Here we describe for the first time the identification and the biological function of the cysteine protease inhibitor cystatin of Fragaria chiloensis, FchCYS1. Based on primary sequence and 3D-structural homology modelling, FchCYS1 is a type II phytocystatin with high identity to other cystatins of the Fragaria genus. Both the papain-like and the legumain-like protease inhibitory domains are indeed functional, based on in vitro assays performed with Escherichia coli protein extracts containing recombinant FchCYS1. FchCYS1 is differentially-expressed in achenes of F. chiloensis fruits, with highest expression as the fruit reaches the ripened stage, suggesting a role in preventing degradation of storage proteins that will nourish the embryo during seed germination. Furthermore, FchCYS1 responds transcriptionally to the application of salicylic acid and to mechanical injury, strongly suggesting that FchCYS1 could be involved in the response against pathogen attack. Overall these results point to a role for FchCYS1 in diverse physiological processes in F. chiloensis.

Glycation induced conformational transitions in cystatin proceed to form biotoxic aggregates: A multidimensional analysis

Hyperglycaemic conditions facilitate the glycation of serum proteins which may have predisposition to aggregation and thus lead to complications. The current study investigates the glycation induced structural and functional modifications of chickpea cystatin (CPC) as well as biological toxicity of the modified protein forms, using CPC-glucose as a model system. Several structural intermediates were formed during the incubation of CPC with glucose (day 4, 8, 12, & 16) as revealed by circular dichroism (CD), altered intrinsic fluorescence, and high ANS binding. Further incubation of CPC with glucose (day 21) formed abundant β structures as revealed by Fourier transform infrared spectroscopy and CD analysis which may be due to the aggregation of protein. High thioflavin T fluorescence intensity and increased Congo red absorbance together with enhanced turbidity and Rayleigh scattering by this modified form confirmed the aggregation. Electron microscopy finally provided the valid physical authentication about the presence of aggregate structures. Functional inactivation of glucose incubated CPC was also observed with time. Single cell electrophoresis of lymphocytes and plasmid nicking assays in the presence of modified CPC showed the DNA damage which confirmed its biological toxicity. Hence, our study suggests that glycation of CPC not only leads to structural and functional alterations in proteins but also to biotoxic AGEs and aggregates.

Phytocystatins: Defense Proteins against Phytophagous Insects and Acari

This review deals with phytocystatins, focussing on their potential role as defence proteins against phytophagous arthropods. Information about the evolutionary, molecular and biochemical features and inhibitory properties of phytocystatins are presented. Cystatin ability to inhibit heterologous cysteine protease activities is commented on as well as some approaches of tailoring cystatin specificity to enhance their defence function towards pests. A general landscape on the digestive proteases of phytophagous insects and acari and the remarkable plasticity of their digestive physiology after feeding on cystatins are highlighted. Biotechnological approaches to produce recombinant cystatins to be added to artificial diets or to be sprayed as insecticide-acaricide compounds and the of use cystatins as transgenes are discussed. Multiple examples and applications are included to end with some conclusions and future perspectives.

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.

Resonance assignments and secondary structure of a phytocystatin from Sesamum indicum

A cDNA encoding a cysteine protease inhibitor, cystatin was cloned from sesame (Sesamum indicum L.) seed. This clone was constructed into an expression vector and expressed in E. coli and purified to homogeneous. The recombinant sesame cystatin (SiCYS) showed effectively inhibitory activity toward C1 cysteine proteases. In order to unravel its inhibitory action from structural point of view, multidimensional heteronuclear NMR techniques were used to characterize the structure of SiCYS. The full (1)H, (15)N, and (13)C resonances of SiCYS were assigned. The secondary structure of SiCYS was identified by using the assigned chemical shifts of (1)H(α), (13)C(α), (13)C(β), and (13)CO through the consensus chemical shift index (CSI). The results of CSI analysis of SiCYS suggest eight β-strands (residues 33-46, 51-61, 63-75, 80-87, 150-155, 157-169, 172-183, and 192-195) and two α-helices (residues 16-30, and 120-135).

Adhiron: a stable and versatile peptide display scaffold for molecular recognition applications

We have designed a novel non-antibody scaffold protein, termed Adhiron, based on a phytocystatin consensus sequence. The Adhiron scaffold shows high thermal stability (T_m ca. 101°C), and is expressed well in Escherichia coli. We have determined the X-ray crystal structure of the Adhiron scaffold to 1.75 Å resolution revealing a compact cystatin-like fold. We have constructed a phage-display library in this scaffold by insertion of two variable peptide regions. The library is of high quality and complexity comprising 1.3 × 10¹⁰ clones. To demonstrate library efficacy, we screened against the yeast Small Ubiquitin-like Modifier (SUMO). In selected clones, variable region 1 often contained sequences homologous to the known SUMO interactive motif (V/I-X-V/I-V/I). Four Adhirons were further characterised and displayed low nanomolar affinities and high specificity for yeast SUMO with essentially no cross-reactivity to human SUMO protein isoforms. We have identified binders against >100 target molecules to date including as examples, a fibroblast growth factor (FGF1), platelet endothelial cell adhesion molecule (PECAM-1; CD31), the SH2 domain Grb2 and a 12-aa peptide. Adhirons are highly stable and well expressed allowing highly specific binding reagents to be selected for use in molecular recognition applications.