Jack bean urease (EC 3.5.1.5) aggregation monitored by dynamic and static light scattering

One enzyme, many faces: urease is also canatoxin

Ureases catalyze the hydrolysis of urea into carbamate and ammonia. Well-conserved proteins, most plant ureases are hexamers of a single chain subunit, like the most abundant isoform of the jack bean (Canavalia ensiformis) urease (JBU). Canatoxin (CNTX) was originally isolated from these seeds as a neurotoxic protein, and later characterized as an isoform of JBU with lower molecular mass and enzyme activity. Inactive CNTX oligomers form upon storage and stabilization of CNTX was achieved by treatment with low concentration of formaldehyde, avoiding its oligomerization. Here, nano-LC-MS/MS-based peptide analysis of CNTX revealed 804 amino acids identical to those of JBU's sequence (840 amino acids). De novo sequencing of CNTX revealed 15 different peptides containing substitution of amino acid residues, denoting CNTX as a product of a paralog gene of JBU. The MS/MS analysis of formaldehyde-treated CNTX showed that amino acid residues located at the trimer-trimer interface of JBU's hexamer were modified. The data confirmed that CNTX is an isoform of JBU and elucidated that stabilization by formaldehyde treatment occurs by modification of amino acids at the protein's surface that prevents the formation of the hexamer and of higher molecular mass inactive aggregates. HIGHLIGHTSCanatoxin (CNTX) is an isoform of jack bean urease (JBU, hexamer of 90 kDa chains)MS/MS sequencing of CNTX showed 804 amino acids identical in JBU (840 residues)Formaldehyde treatment of CNTX stabilizes its toxicity and avoids oligomerizationModified amino acid residues in CNTX are at the trimer-trimer interface of JBUCommunicated by Ramaswamy H. Sarma.

The neurotoxic mechanism of Jack Bean Urease in insects involves the interplay between octopaminergic and dopaminergic pathways

In the last decades, the entomotoxicity of JBU and its derived peptides became an object of study, due mainly to the ubiquitous interaction of these compounds with different species of insects and their potential as natural insecticides. In this work, we investigated the neurotoxic effects of JBU in Nauphoeta cinerea cockroaches by dissecting pharmacologically the monoaminergic pathways involved. Selective pharmacological modulators for monoaminergic pathways in in vivo and ex vivo experimental models were employed. Thus, the analysis of N. cinerea neurolocomotory behavior demonstrated that JBU (1.5 and 3 μg/g) induces a significant decrease in the exploratory activity. In these assays, pretreatment of animals with phentolamine, SCH23390 or reserpine, interfered significantly with the response of JBU. Using in vivo abductor metathoracic preparations JBU (1.5 μg/g) induced progressive neuromuscular blockade, in 120 min recordings. In this set of experiments, the previous treatment of the animals with phentolamine, SCH23390 or reserpine, completely inhibited JBU-induced neuromuscular blockade. The recordings of spontaneous compound neural action potentials in N. cinerea legs showed that JBU, only in the smallest dose, significantly decreased the number of potentials in 60 min recordings. When the animals were pretreated with phentolamine, SCH23390, or reserpine, but not with mianserin, there was a significant prevention of the JBU-inhibitory responses on the action potentials firing. Meanwhile, the treatment of the animals with mianserin did not affect JBU's inhibitory activity. The data presented in this work strongly suggest that the neurotoxic response of JBU in N. cinerea involves a cross talking between OCTOPAMIN-ergic and DOPAMIN-ergic nerve systems, but not the SEROTONIN-ergic neurotransmission. Further molecular biology studies with expression of insect receptors associated with voltage clamp techniques will help to discriminate the selectivity of JBU over the monoaminergic transmission.

Enzyme Purification Improves the Enzyme Loading, Self-Propulsion, and Endurance Performance of Micromotors

Enzyme-powered micro- and nanomotors make use of biocatalysis to self-propel in aqueous media and hold immense promise for active and targeted drug delivery. Most (if not all) of these micro- and nanomotors described to date are fabricated using a commercially available enzyme, despite claims that some commercial preparations may not have a sufficiently high degree of purity for downstream applications. In this study, the purity of a commercial urease, an enzyme frequently used to power the motion of micro- and nanomotors, was evaluated and found to be impure. After separating the hexameric urease from the protein impurities by size-exclusion chromatography, the hexameric urease was subsequently characterized and used to functionalize hollow silica microcapsules. Micromotors loaded with purified urease were found to be 2.5 times more motile than the same micromotors loaded with unpurified urease, reaching average speeds of 5.5 μm/s. After comparing a number of parameters, such as enzyme distribution, protein loading, and motor reusability, between micromotors functionalized with purified vs unpurified urease, it was concluded that protein purification was essential for optimal performance of the enzyme-powered micromotor.

Origin, Succession, and Control of Biotoxin in Wine

Wine is a worldwide alcoholic beverage with antioxidant active substances and complex flavors. Moderate drinking of wine has been proven to be beneficial to health. However, wine has some negative components, such as residual pesticides, heavy metals, and biotoxins. Of these, biotoxins from microorganisms were characterized as the most important toxins in wine. Wine fermentation mainly involves alcoholic fermentation, malolactic fermentation, and aging, which endue wine with complex flavors and even produce some undesirable metabolites. These metabolites cause potential safety risks that are not thoroughly understood. This review aimed to investigate the origin, evolution, and control technology of undesirable metabolites (e.g., ochratoxin A, ethyl carbamate, and biogenic amines) in wine. It also highlighted current wine industry practices of minimizing the number of biotoxins in wine.

Neurotoxic and convulsant effects induced by jack bean ureases on the mammalian nervous system

Ureases are microbial virulence factors either because of the enzymatic release of ammonia or due to many other non-enzymatic effects. Here we studied two neurotoxic urease isoforms, Canatoxin (CNTX) and Jack Bean Urease (JBU), produced by the plant Canavalia ensiformis, whose mechanisms of action remain elusive. The neurotoxins provoke convulsions in rodents (LD₅₀ ∼2 mg/kg) and stimulate exocytosis in cell models, affecting intracellular calcium levels. Here, electrophysiological and brain imaging techniques were applied to elucidate their mode of action. While systemic administration of the toxins causes tonic-clonic seizures in rodents, JBU injected into rat hippocampus induced spike-wave discharges similar to absence-like seizures. JBU reduced the amplitude of compound action potential from mouse sciatic nerve in a tetrodotoxin-insensitive manner. Hippocampal slices from CNTX-injected animals or slices treated in vitro with JBU failed to induce long term potentiation upon tetanic stimulation. Rat cortical synaptosomes treated with JBU released L-glutamate. JBU increased the intracellular calcium levels and spontaneous firing rate in rat hippocampus neurons. MicroPET scans of CNTX-injected rats revealed increased ^[18]Fluoro-deoxyglucose uptake in epileptogenesis-related areas like hippocampus and thalamus. Curiously, CNTX did not affect voltage-gated sodium, calcium or potassium channels currents, neither did it interfere on cholinergic receptors, suggesting an indirect mode of action that could be related to the ureases' membrane-disturbing properties. Understanding the neurotoxic mode of action of C. ensiformis ureases could help to unveil the so far underappreciated relevance of these toxins in diseases caused by urease-producing microorganisms, in which the human central nervous system is affected.

Novel thiobarbiturates as potent urease inhibitors with potential antibacterial activity: Design, synthesis, radiolabeling and biodistribution study

Urease enzyme is a virulence factor that helps in colonization and maintenance of highly pathogenic bacteria in human. Hence, the inhibition of urease enzymes is well-established to be a promising approach for preventing deleterious effects of ureolytic bacterial infections. In this work, novel thiobarbiturate derivatives were synthesized and evaluated for their urease inhibitory activity. All tested compounds effectively inhibited the activity of urease enzyme. Compounds 1, 2a, 2b, 4 and 9 displayed remarkable anti-urease activity (IC₅₀ = 8.21-16.95 μM) superior to that of thiourea reference standard (IC₅₀ = 20.04 μM). Moreover, compounds 3a, 3g, 5 and 8 were equipotent to thiourea. Among the tested compounds, morpholine derivative 4 (IC₅₀ = 8.21 µM) was the most potent one, showing 2.5 folds the activity of thiourea. In addition, the antibacterial activity of the synthesized compounds was estimated against both standard strains and clinical isolates of urease producing bacteria. Compound 4 explored the highest potency exceeding that of cephalexin reference drug. Moreover, biodistribution study using radiolabeling approach revealed a remarked uptake of ^99mTc-compound 4 into infection induced in mice. Furthermore, a molecular docking analysis revealed proper orientation of title compounds into the urease active site rationalizing their potent anti-urease activity.

Enhanced Diffusion and Chemotaxis of Enzymes

Many enzymes appear to diffuse faster in the presence of substrate and to drift either up or down a concentration gradient of their substrate. Observations of these phenomena, termed enhanced enzyme diffusion (EED) and enzyme chemotaxis, respectively, lead to a novel view of enzymes as active matter. Enzyme chemotaxis and EED may be important in biology and could have practical applications in biotechnology and nanotechnology. They are also of considerable biophysical interest; indeed, their physical mechanisms are still quite uncertain. This review provides an analytic summary of experimental studies of these phenomena and of the mechanisms that have been proposed to explain them and offers a perspective on future directions for the field.

Urea removal strategies for dialysate regeneration in a wearable artificial kidney

The availability of a wearable artificial kidney (WAK) that provides dialysis outside the hospital would be an important advancement for dialysis patients. The concept of a WAK is based on regeneration of a small volume of dialysate in a closed-loop. Removal of urea, the primary waste product of nitrogen metabolism, is the major challenge for the realization of a WAK since it is a molecule with low reactivity that is difficult to adsorb while it is the waste solute with the highest daily molar production. Currently, no efficient urea removal technology is available that allows for miniaturization of the WAK to a size and weight that is acceptable for patients to carry. Several urea removal strategies have been explored, including enzymatic hydrolysis by urease, electro-oxidation and sorbent systems. However, thus far, these methods have toxic side effects, limited removal capacity or slow removal kinetics. This review discusses different urea removal strategies for application in a wearable dialysis device, from both a chemical and a medical perspective.

Enzyme-Functionalized Piezoresistive Hydrogel Biosensors for the Detection of Urea

Urea is used in a wide variety of industrial applications such as the production of fertilizers. Furthermore, urea as a metabolic product is an important indicator in biomedical diagnostics. For these applications, reliable urea sensors are essential. In this work, we present a novel hydrogel-based biosensor for the detection of urea. The hydrolysis of urea by the enzyme urease leads to an alkaline pH change, which is detected with a pH-sensitive poly(acrylic acid-co-dimethylaminoethyl methacrylate) hydrogel. For this purpose, the enzyme is physically entrapped during polymerization. This enzyme-hydrogel system shows a large sensitivity in the range from 1 mmol/L up to 20 mmol/L urea with a high long-term stability over at least eight weeks. Furthermore, this urea-sensitive hydrogel is highly selective to urea in comparison to similar species like thiourea or N-methylurea. For sensory applications, the swelling pressure of this hydrogel system is transformed via a piezoresistive pressure sensor into a measurable output voltage. In this way, the basic principle of hydrogel-based piezoresistive urea biosensors was demonstrated.

Enhanced Diffusion of Catalytically Active Enzymes

The past decade has seen an increasing number of investigations into enhanced diffusion of catalytically active enzymes. These studies suggested that enzymes are actively propelled as they catalyze reactions or bind with ligands (e.g., substrates or inhibitors). In this Outlook, we chronologically summarize and discuss the experimental observations and theoretical interpretations and emphasize the potential contradictions in these efforts. We point out that the existing multimeric forms of enzymes or isozymes may cause artifacts in measurements and that the conformational changes upon substrate binding are usually not sufficient to give rise to a diffusion enhancement greater than 30%. Therefore, more rigorous experiments and a more comprehensive theory are urgently needed to quantitatively validate and describe the enhanced enzyme diffusion.

Utility of anthranilic acid and diethylacetylenedicarboxylate for the synthesis of nitrogenous organo/organometallic compounds as urease inhibitors

Fumarate diester 3 was synthesized upon reacting anthranilic acid with diethylacetylenedicarboxylate. Compound 3 was reacted with different nucleophiles in mild reaction conditions. Selected reaction routes that afforded products 6, 9, 10, 11, and 12 were explained. The estimated mechanism for the reaction of 3 with ethylenediamine to afford 9 was proved by X-ray single-crystal and retro-synthetic reaction. Acetyl anthranilic acid was utilized with zinc and copper to afford the organometallic compounds 14a and 14b, respectively. Three single crystals were afforded for 3, 9 and the organocopper complex 14b. Target compounds were screened for their inhibitory potential against urease enzyme. Most compounds were more potent than thiourea as standard inhibitor, considering that oxopiperazine 9 exhibited double the activity: IC₅₀ = 8.16 ± 0.65 µM (thiourea IC₅₀ = 20.04 ± 0.33 µM). Docking studies were in agreement with the in vitro enzyme assay.

A Thermodynamic Limit on the Role of Self-Propulsion in Enhanced Enzyme Diffusion

A number of enzymes reportedly exhibit enhanced diffusion in the presence of their substrates, with a Michaelis-Menten-like concentration dependence. Although no definite explanation of this phenomenon has emerged, a physical picture of enzyme self-propulsion using energy from the catalyzed reaction has been widely considered. Here, we present a kinematic and thermodynamic analysis of enzyme self-propulsion that is independent of any specific propulsion mechanism. Using this theory, along with biophysical data compiled for all enzymes so far shown to undergo enhanced diffusion, we show that the propulsion speed required to generate experimental levels of enhanced diffusion exceeds the speeds of well-known active biomolecules, such as myosin, by several orders of magnitude. Furthermore, the minimal power dissipation required to account for enzyme enhanced diffusion by self-propulsion markedly exceeds the chemical power available from enzyme-catalyzed reactions. Alternative explanations for the observation of enhanced enzyme diffusion therefore merit stronger consideration.

Catalytic enzymes are active matter

Catalysis and mobility of reactants in fluid are normally thought to be decoupled. Violating this classical paradigm, this paper presents the catalyst laws of motion. Comparing experimental data to the theory presented here, we conclude that part of the free energy released by chemical reaction is channeled into driving catalysts to execute wormlike trajectories by piconewton forces performing work of a few k_BT against fluid viscosity, where the rotational diffusion rate dictates the trajectory persistence length. This active motion agitates the fluid medium and produces antichemotaxis, the migration of catalyst down the gradient of the reactant concentration. Alternative explanations of enhanced catalyst mobility are examined critically.

Using a microscopic theory to analyze experiments, we demonstrate that enzymes are active matter. Superresolution fluorescence measurements—performed across four orders of magnitude of substrate concentration, with emphasis on the biologically relevant regime around or below the Michaelis–Menten constant—show that catalysis boosts the motion of enzymes to be superdiffusive for a few microseconds, enhancing their effective diffusivity over longer timescales. Occurring at the catalytic turnover rate, these fast ballistic leaps maintain direction over a duration limited by rotational diffusion, driving enzymes to execute wormlike trajectories by piconewton forces performing work of a few k_BT against viscosity. The boosts are more frequent at high substrate concentrations, biasing the trajectories toward substrate-poor regions, thus exhibiting antichemotaxis, demonstrated here experimentally over a wide range of aqueous concentrations. Alternative noncatalytic, passive mechanisms that predict chemotaxis, cross-diffusion, and phoresis, are critically analyzed. We examine the physical interpretation of our findings, speculate on the underlying mechanism, and discuss the avenues they open with biological and technological implications. These findings violate the classical paradigm that chemical reaction and motility are distinct processes, and suggest reaction–motion coupling as a general principle of catalysis.

HullRad: Fast Calculations of Folded and Disordered Protein and Nucleic Acid Hydrodynamic Properties

Hydrodynamic properties are useful parameters for estimating the size and shape of proteins and nucleic acids in solution. The calculation of such properties from structural models informs on the solution properties of these molecules and complements corresponding structural studies. Here we report, to our knowledge, a new method to accurately predict the hydrodynamic properties of molecular structures. This method uses a convex hull model to estimate the hydrodynamic volume of the molecule and is orders of magnitude faster than common methods. It works well for both folded proteins and ensembles of conformationally heterogeneous proteins and for nucleic acids. Because of its simplicity and speed, the method should be useful for the modification of computer-generated, intrinsically disordered protein ensembles and ensembles of flexible, but folded, molecules in which rapid calculation of experimental parameters is needed. The convex hull method is implemented in a Python script called HullRad. The use of the method is facilitated by a web server and the code is freely available for batch applications.

Enzyme leaps fuel antichemotaxis

There is mounting evidence that enzyme diffusivity is enhanced when the enzyme is catalytically active. Here, using superresolution microscopy [stimulated emission-depletion fluorescence correlation spectroscopy (STED-FCS)], we show that active enzymes migrate spontaneously in the direction of lower substrate concentration ("antichemotaxis") by a process analogous to the run-and-tumble foraging strategy of swimming microorganisms and our theory quantifies the mechanism. The two enzymes studied, urease and acetylcholinesterase, display two families of transit times through subdiffraction-sized focus spots, a diffusive mode and a ballistic mode, and the latter transit time is close to the inverse rate of catalytic turnover. This biochemical information-processing algorithm may be useful to design synthetic self-propelled swimmers and nanoparticles relevant to active materials. Executed by molecules lacking the decision-making circuitry of microorganisms, antichemotaxis by this run-and-tumble process offers the biological function to homogenize product concentration, which could be significant in situations when the reactant concentration varies from spot to spot.

Interaction of jack bean (Canavalia ensiformis) urease and a derived peptide with lipid vesicles

Ureases are metalloenzymes that catalyze the hydrolysis of urea to ammonia and carbon dioxide. Jack bean (Canavalia ensiformis) produces three isoforms of urease (Canatoxin, JBU and JBURE-II). Canatoxin and JBU display several biological properties independent of their ureolytic activity, such as neurotoxicity, exocytosis-inducing and pro-inflammatory effects, blood platelets activation, insecticidal and antifungal activities. The Canatoxin entomotoxic activity is mostly due to an internal peptide, named pepcanatox, released upon the hydrolysis of the protein by insect cathepsin-like digestive enzymes. Based on pepcanatox sequence, Jaburetox-2Ec was produced in Escherichia coli. JBU and its peptides were shown to permeabilize membranes through an ion channel-based mechanism. Here we studied the JBU and Jaburetox-2Ec interaction with platelet-like multilamellar liposomes (PML) using Dynamic Light Scattering and Small Angle X-ray Scattering techniques. We also analyzed the interaction of JBU with giant unilamellar vesicles (GUVs) using Fluorescence Microscopy. The interaction of vesicles with JBU led to a slight reduction of hydrodynamic radius, and caused an increase in the lamellar repeat distance of PML, suggesting a membrane disordering effect. In contrast, Jaburetox-2Ec decreased the lamellar repeat distance of PML membranes, while also diminishing their hydrodynamic radius. Fluorescence microscopy showed that the interaction of GUVs with JBU caused membrane perturbation with formation of tethers. In conclusion, JBU can interact with PML, probably by inserting its Jaburetox "domain" into the PML external membrane. Additionally, the interaction of Jaburetox-2Ec affects the vesicle's internal bilayers and hence causes more drastic changes in the PML membrane organization in comparison with JBU.

Enzyme encapsulation in zeolitic imidazolate frameworks: a comparison between controlled co-precipitation and biomimetic mineralisation

Recent studies have demonstrated that metal–organic frameworks can be employed as protective coatings for enzymes.

Andrographolide sodium bisulphite-induced inactivation of urease: inhibitory potency, kinetics and mechanism

BACKGROUND

The inhibitory effect of andrographolide sodium bisulphite (ASB) on jack bean urease (JBU) and Helicobacter pylori urease (HPU) was performed to elucidate the inhibitory potency, kinetics and mechanism of inhibition in 20 mM phosphate buffer, pH 7.0, 2 mM EDTA, 25 °C.

METHODS

The ammonia formations, indicator of urease activity, were examined using modified spectrophotometric Berthelot (phenol-hypochlorite) method. The inhibitory effect of ASB was characterized with IC50 values. Lineweaver-Burk and Dixon plots for JBU inhibition of ASB was constructed from the kinetic data. SH-blocking reagents and competitive active site Ni2+ binding inhibitors were employed for mechanism study. Molecular docking technique was used to provide some information on binding conformations as well as confirm the inhibition mode.

RESULTS

The IC50 of ASB against JBU and HPU was 3.28±0.13 mM and 3.17±0.34 mM, respectively. The inhibition proved to be competitive and concentration- dependent in a slow-binding progress. The rapid formation of initial ASB-JBU complex with an inhibition constant of Ki=2.86×10(-3) mM was followed by a slow isomerization into the final complex with an overall inhibition constant of Ki*=1.33×10(-4) mM. The protective experiment proved that the urease active site is involved in the binding of ASB. Thiol reagents (L-cysteine and dithiothreithol) strongly protect the enzyme from the loss of enzymatic activity, while boric acid and fluoride show weaker protection, indicating that the active-site sulfhydryl group of JBU was potentially involved in the blocking process. Moreover, inhibition of ASB proved to be reversible since ASB-inactivated JBU could be reactivated by dithiothreitol application. Molecular docking assay suggested that ASB made contacts with the important sulfhydryl group Cys-592 residue and restricted the mobility of the active-site flap.

CONCLUSIONS

ASB was a competitive inhibitor targeting thiol groups of urease in a slow-binding manner both reversibly and concentration-dependently, serving as a promising urease inhibitor for the treatment of urease-related diseases.

Design and synthesis of new barbituric- and thiobarbituric acid derivatives as potent urease inhibitors: Structure activity relationship and molecular modeling studies

In this study 36 new compounds were synthesized by condensing barbituric acid or thiobarbituric acid and respective anilines (bearing different substituents) in the presence of triethyl orthoformate in good yields. In vitro urease inhibition studies against jack bean urease revealed that barbituric acid derived compounds (1-9 and 19-27) were found to exhibit low to moderate activity however thiobarbituric acid derived compounds (10-18 and 28-36) showed significant inhibition activity at low micro-molar concentrations. Among the synthesized compounds, compounds (15), (12), (10), (36), (16) and (35) showed excellent urease inhibition with IC50 values 8.53 ± 0.027, 8.93 ± 0.027, 12.96 ± 0.13, 15 ± 0.098, 18.9 ± 0.027 and 19.7 ± 0.63 μM, respectively, even better than the reference compound thiourea (IC50 = 21 ± 0.011). The compound (11) exhibited comparable activity to the standard with IC50 value 21.83 ± 0.19 μM. In silico molecular docking studies for most active compounds (10), (12), (15), (16), (35) and (36) and two inactive compounds (3) and (6) were performed to predict the binding patterns.

Substrate catalysis enhances single-enzyme diffusion

We show that diffusion of single urease enzyme molecules increases in the presence of urea in a concentration-dependent manner and calculate the force responsible for this increase. Urease diffusion measured using fluorescence correlation spectroscopy increased by 16-28% over buffer controls at urea concentrations ranging from 0.001 to 1 M. This increase was significantly attenuated when urease was inhibited with pyrocatechol, demonstrating that the increase in diffusion was the result of enzyme catalysis of urea. Local molecular pH changes as measured using the pH-dependent fluorescence lifetime of SNARF-1 conjugated to urease were not sufficient to explain the increase in diffusion. Thus, a force generated by self-electrophoresis remains the most plausible explanation. This force, evaluated using Brownian dynamics simulations, was 12 pN per reaction turnover. These measurements demonstrate force generation by a single enzyme molecule and lay the foundation for a further understanding of biological force generation and the development of enzyme-driven nanomotors.

Solution behavior and activity of a halophilic esterase under high salt concentration

Background

Halophiles are extremophiles that thrive in environments with very high concentrations of salt. Although the salt reliance and physiology of these extremophiles have been widely investigated, the molecular working mechanisms of their enzymes under salty conditions have been little explored.

Methodology/Principal Findings

A halophilic esterolytic enzyme LipC derived from archeaon Haloarcula marismortui was overexpressed from Escherichia coli BL21. The purified enzyme showed a range of hydrolytic activity towards the substrates of p-nitrophenyl esters with different alkyl chains (n = 2−16), with the highest activity being observed for p-nitrophenyl acetate, consistent with the basic character of an esterase. The optimal esterase activities were found to be at pH 9.5 and [NaCl] = 3.4 M or [KCl] = 3.0 M and at around 45°C. Interestingly, the hydrolysis activity showed a clear reversibility against changes in salt concentration. At the ambient temperature of 22°C, enzyme systems working under the optimal salt concentrations were very stable against time. Increase in temperature increased the activity but reduced its stability. Circular dichroism (CD), dynamic light scattering (DLS) and small angle neutron scattering (SANS) were deployed to determine the physical states of LipC in solution. As the salt concentration increased, DLS revealed substantial increase in aggregate sizes, but CD measurements revealed the maximal retention of the α-helical structure at the salt concentration matching the optimal activity. These observations were supported by SANS analysis that revealed the highest proportion of unimers and dimers around the optimal salt concentration, although the coexistent larger aggregates showed a trend of increasing size with salt concentration, consistent with the DLS data.

Conclusions/Significance

The solution α-helical structure and activity relation also matched the highest proportion of enzyme unimers and dimers. Given that all the solutions studied were structurally inhomogeneous, it is important for future work to understand how the LipC's solution aggregation affected its activity.

Purification, crystallization and preliminary X-ray analysis of urease from jack bean (Canavalia ensiformis)

Plant urease is a seed protein that is common in most legumes. It is also common in many bacteria and fungi and several species of yeast. Urease allows organisms to use exogenous and internally generated urea as a nitrogen source by catalyzing the hydrolysis of urea to ammonia and carbon dioxide. Urease from jack bean meal was purified to electrophoretic homogeneity using a series of steps involving acetone precipitation and size-exclusion and ion-exchange chromatography. The jack bean urease was crystallized and the resulting crystals diffracted to 2.05 A resolution using synchrotron radiation. The crystals belonged to the hexagonal space group P6(3)22, with unit-cell parameters a = b = 138.57, c = 198.36 A.

Invitro effect of Canavalia ensiformis urease and the derived peptide Jaburetox-2Ec on Rhodnius prolixus Malpighian tubules

Ureases are metalloenzymes that are widespread among plants, fungi and bacteria. Urease isoforms (jack bean urease-JBU and canatoxin) from Canavalia ensiformis seeds are toxic to insects and fungi, suggesting a role in plant defense. The entomotoxic effect is due to the release of a 10-kDa peptide by cathepsin-like enzymes in the insect's midgut. Urease causes a decrease in post-feeding weight loss in Rhodnius prolixus, suggesting an effect on water balance. To investigate how this impairment occurs, we have evaluated the action of JBU and the urease-derivated peptide Jaburetox-2Ec on R. prolixus Malpighian tubules and also investigated the involvement of second messengers. JBU and Jaburetox-2Ec affect serotonin-induced secretion from Malpighian tubules. This effect is not cAMP-dependent, but the Jaburetox-2Ec effect is cGMP-dependent. Eicosanoid metabolites and calcium ions appear to be involved in JBU effect on diuresis, but are not involved in the action of Jaburetox-2Ec. Jaburetox-2Ec, but not JBU, causes a change in the transepithelial potential of the tubules. Canatoxin has a similar effect on tubules secretion, decreasing the secretion rate, but the urease from Helicobacter pylori has no significant effect. These data are helpful in our understanding of the actions of ureases and derived peptides on insects, and also reinforces the potential use of these proteins as biopesticides.

Mechanism of suppression of protein aggregation by α-crystallin

This review summarizes experimental data illuminating the mechanism of suppression of heat-induced protein aggregation by alpha-crystallin, one of the small heat shock proteins. The dynamic light scattering data show that the initial stage of thermal aggregation of proteins is the formation of the initial aggregates involving hundreds of molecules of the denatured protein. Further sticking of the starting aggregates proceeds in a regime of diffusion-limited cluster-cluster aggregation. The protective effect of alpha-crystallin is due to transition of the aggregation process to the regime of reaction-limited cluster-cluster aggregation, wherein the sticking probability for the colliding particles becomes lower than unity.

Insights into the role and structure of plant ureases

The broad distribution of ureases in leguminous seeds, as well as the accumulation pattern of the protein during seed maturation, are suggestive of an important physiological role for this enzyme. Since the isolation and characterization of jack bean urease by Sumner in 1926, many investigations have been dedicated to the structural and biological features of this enzyme; nevertheless, many questions still remain. It has been reported that ureases from plants (jack bean and soybean seeds) display biological properties unrelated to their ureolytic activity, notably a high insecticidal activity against Coleoptera (beetles) and Hemiptera (bugs), suggesting that ureases might be involved in plant defense. Besides the insecticidal activity, canatoxin, a jack bean urease isoform, causes convulsions and death in mice and rats, induces indirect hemagglutination (hemilectin activity) and promotes exocytosis in several cell types. Not only plant ureases but also some microbial ureases (found in Bacillus pasteurii and Helicobacter pylori) are able to induce activation of platelets in a process mediated by lipoxygenase-derived metabolites. This review summarizes the biological and structural properties of plant ureases, compares them with those displayed by bacterial ureases, and discusses the significance of these findings.

Mechanism of thermal aggregation of rabbit muscle glyceraldehyde-3-phosphate dehydrogenase

Thermal denaturation and aggregation of rabbit muscle glyceraldehyde-3-phosphate dehydrogenase (GAPDH) have been studied using differential scanning calorimetry (DSC), dynamic light scattering (DLS), and analytical ultracentrifugation. The maximum of the protein thermal transition (T(m)) increased with increasing the protein concentration, suggesting that the denaturation process involves the stage of reversible dissociation of the enzyme tetramer into the oligomeric forms of lesser size. The dissociation of the enzyme tetramer was shown by sedimentation velocity at 45 degrees C. The DLS data support the mechanism of protein aggregation that involves a stage of the formation of the start aggregates followed by their sticking together. The hydrodynamic radius of the start aggregates remained constant in the temperature interval from 37 to 55 degrees C and was independent of the protein concentration (R(h,0) approximately 21 nm; 10 mM sodium phosphate, pH 7.5). A strict correlation between thermal aggregation of GAPDH registered by the increase in the light scattering intensity and protein denaturation characterized by DSC has been proved.

The study of amorphous aggregation of tobacco mosaic virus coat protein by dynamic light scattering

The kinetics of heat-induced and cetyltrimethylammonium bromide induced amorphous aggregation of tobacco mosaic virus coat protein in Na(+)/Na(+) phosphate buffer, pH 8.0, have been studied using dynamic light scattering. In the case of thermal aggregation (52 degrees C) the character of the dependence of the hydrodynamic radius (R(h)) on time indicates that at certain instant the population of aggregates is split into two components. The size of the aggregates of one kind remains practically constant in time, whereas the size of aggregates of other kind increases monotonously in time reaching the values characteristic of aggregates prone to precipitation (R(h)=900-1500 nm). The construction of the light scattering intensity versus R(h) plots shows that the large aggregates (the start aggregates) exist in the system at the instant the initial increase in the light scattering intensity is observed. For thermal aggregation the R(h) value for the start aggregates is independent of the protein concentration and equal to 21.6 nm. In the case of the surfactant-induced aggregation (at 25 degrees C) no splitting of the aggregates into two components is observed and the size of the start aggregates turns out to be much larger (107 nm) than on the thermal aggregation. The dependence of R(h) on time for both heat-induced aggregation and surfactant-induced aggregation after a lapse of time follows the power law indicating that the aggregation process proceeds in the kinetic regime of diffusion-limited cluster-cluster aggregation. Fractal dimension is close to 1.8. The molecular chaperone alpha-crystallin does not affect the kinetics of tobacco mosaic virus coat protein thermal aggregation.

Mechanism of chaperone-like activity. Suppression of thermal aggregation of betaL-crystallin by alpha-crystallin

Thermal denaturation and aggregation of beta(L)-crystallin from bovine lens have been studied using differential scanning calorimetry (DSC) and dynamic light scattering (DLS). According to the DLS data, the distribution of the beta(L)-crystallin aggregates by their hydrodynamic radius (R(h)) remains monomodal to the point of precipitating aggregates (sodium phosphate, pH 6.8; 100 mM NaCl; 60 degrees C). The size of the start aggregates (R(h,0)) and duration of the latent stage (t(0)) leading to the formation of the start aggregates have been determined from the light scattering intensity versus the hydrodynamic radius plots and the dependences of R(h) on time. The R(h,0) value remains constant at variation of the beta(L)-crystallin concentration, whereas the t(0) value increases with diminishing beta(L)-crystallin concentration. The suppression of beta(L)-crystallin aggregation by alpha-crystallin is connected with the decrease in the R(h,0) value and increase in the t(0) value. In the presence of alpha-crystallin the aggregate population is split into two components. The first component is represented by stable aggregates whose size remains constant in time. The aggregates of the other kind grow until they reach the size characteristic of aggregates prone to precipitation. The DSC data show that alpha-crystallin has no appreciable influence on thermal denaturation of beta(L)-crystallin.

Studying Protein Aggregation by Programmed Flow Field-Flow Fractionation Using Ceramic Hollow Fibers

Ceramic hollow fibers have been used as separation channels for flow field-flow fractionation. The fibers were made of alpha-alumina, with a gamma-alumina layer on the inside wall acting as a semipermeable (ultrafiltration) membrane. The fibers and the separation system were tested by determining the diffusion coefficients of a series of standard proteins under various experimental conditions. Even for the smallest protein studied, a complete recovery from the fiber was obtained. A single fiber could be used for several months without problems such as leakage or fouling. The precision of the diffusion coefficient measurements was in the order of 5-10%. A good agreement with literature data was found. Programming of the cross-flow, with a time-delayed exponential decay program, was applied to extend the accessible size range for the sample components. With flow programming, the observed retention times increased linearly with the logarithm of the molar mass of proteins and aggregates, as predicted by theory. Heat-induced aggregation of beta-lactoglobulin (beta-LG) in aqueous solution was studied with the system. Upon heating, not only the extent of aggregation but also the size of the beta-LG aggregates was found to increase with the original concentration of beta-LG in solution and with the heating time. After heating in the presence of salt, very large aggregates were formed, with molar masses over 100 million. A multiangle light scattering detector was used to estimate molar masses and sizes of the protein aggregates. From the relation between the apparent diffusion coefficients and the molar masses of the aggregates, as well as from the ratio of the rms (scattering) and the hydrodyamic radii, it was concluded that the larger beta-LG aggregates behave as flexible chains in solution.

Effect of chemical modification of histidines on the copper-induced oligomerization of jack bean urease (EC 3.5.1.5)

Aggregation of jack bean urease (JBU) is associated with alterations of its biological properties, notably the ureolytic and entomotoxic activities. We investigated the influence of metals on protein oligomerization and biological properties. Besides protein aggregation, Cu(2+) induces inhibition of both ureolytic and insecticidal activities of JBU. Chemical modification of histidine residues in JBU with diethylpyrocarbonate (DEPC) decreases its affinity for Cu(2+) and inhibits oligomerization induced by this metal. Furthermore, this modification protects the insecticidal properties of JBU from being inactivated by Cu(2+). Although DEPC-treated JBU displayed lower ureolytic activity, the modified protein is less susceptible to inhibition by Cu(2+) when compared to native enzyme. Our findings show that Cu(2+) promotes JBU aggregation and differently of other heavy metals studied here, it apparently inhibits the ureolytic activity by inducing protein polymerization along with blockage of sulfhydryl groups.