Zinc Switch in Pig Heart Lipoamide Dehydrogenase: Steady-State and Transient Kinetic Studies of the Diaphorase Reaction.

Elevation of intracellular Zn2+ following ischemia contributes to cell death by affecting mitochondrial function. Zn2+ is a differential regulator of the mitochondrial enzyme lipoamide dehydrogenase (LADH) at physiological concentrations (Ka = 0.1 µM free zinc), inhibiting lipoamide and accelerating NADH dehydrogenase activities. These differential effects have been attributed to coordination of Zn2+ by LADH active-site cysteines. A detailed kinetic mechanism has now been developed for the diaphorase (NADH-dehydrogenase) reaction catalyzed by pig heart LADH using 2,6-dichlorophenol-indophenol (DCPIP) as a model quinone electron acceptor. Anaerobic stopped-flow experiments show that two-electron reduced LADH is 15-25-fold less active towards DCPIP reduction than four-electron reduced enzyme, or Zn2+-modified reduced LADH (the corresponding values of the rate constants are (6.5 ± 1.5) × 103 M-1·s-1, (9 ± 2) × 104 M-1·s-1, and (1.6 ± 0.5) × 105 M-1·s-1, respectively). Steady-state kinetic studies with different diaphorase substrates show that Zn2+ accelerates reaction rates exclusively for two-electron acceptors (duroquinone, DCPIP), but not for one-electron acceptors (benzoquinone, ubiquinone, ferricyanide). This implies that the two-electron reduced form of LADH, prevalent at low NADH levels, is a poor two-electron donor compared to the four-electron reduced or Zn2+-modified reduced LADH forms. These data suggest that zinc binding to the active-site thiols switches the enzyme from one- to two-electron donor mode. This zinc-activated switch has the potential to alter the ratio of superoxide and H2O2 generated by the LADH oxidase activity.

Multilayer polyion complex nanoformulations of superoxide dismutase 1 for acute spinal cord injury.

As one of the most devastating forms of trauma, spinal cord injury (SCI) remains a challenging clinical problem. The secondary processes associated with the primary injury, such as overproduction of reactive oxygen species (ROS) and inflammation, lead to concomitant compression of the injured spinal cord and neuronal death. Delivery of copper-zinc superoxide dismutase (SOD1), an efficient ROS scavenger, to the site of injury can mitigate SCI-induced oxidative stress and tissue damage. Towards this goal catalytically active nanoformulations of SOD1 ("nanozymes") are developed as a modality for treatment of SCI. Along with the cross-linked polyion complex of SOD1 with polycation poly(ethylene glycol) (PEG)-polylysine (single-coat (SC) nanozyme), we introduce for the first time the chemically cross-linked multilayer polyion complex in which SOD1 is first incorporated into a polyion complex with polycation, then coated by anionic block copolymer, PEG-polyglutamic acid (double-coat (DC) nanozyme). We developed DC nanozymes with high enzymatic activity and ability to retain and protect SOD1 under physiological conditions. Pharmacokinetic study revealed that DC nanozymes significantly prolonged circulation of active SOD1 in the blood stream compared to free SOD1 or SC nanozymes (half-life was 60 vs 6min). Single intravenous injection of DC nanozymes (5kU of SOD1/kg) improved the recovery of locomotor functions in rats with moderate SCI, along with reduction of swelling, concomitant compression of the spinal cord and formation of post-traumatic cysts. Thus, based on the testing in a rodent model the SOD1 DC nanozymes are promising modality for scavenging ROS, decreasing inflammation and edema, and improving recovery after SCI.

Dual Active Site in the Endolytic Transglycosylase gp144 of Bacteriophage phiKZ.

Lytic transglycosylases are abundant peptidoglycan lysing enzymes that degrade the heteropolymers of bacterial cell walls in metabolic processes or in the course of a bacteriophage infection. The conventional catalytic mechanism of transglycosylases involves only the Glu or Asp residue. Endolysin gp144 of Pseudomonas aeruginosa bacteriophage phiKZ belongs to the family of Gram-negative transglycosylases with a modular composition and C-terminal location of the catalytic domain. Glu115 of gp144 performs the predicted role of a catalytic residue. However, replacement of this residue does not completely eliminate the activity of the mutant protein. Site-directed mutagenesis has revealed the participation of Tyr197 in the catalytic mechanism, as well as the presence of a second active site involving Glu178 and Tyr147. The existence of the dual active site was supported by computer modeling and monitoring of the molecular dynamics of the changes in the conformation and surface charge distribution as a consequence of point mutations.

Enzymes of SPZ7 phage: isolation and properties.

Bacteriophage enzyme preparations exolysin and endolysin were studied. Exolysin (a phage-associated enzyme) was obtained from tail fraction and endolysin from phage-free cytoplasmic fraction of disintegrated Salmonella enteritidis cells. A new method for purification of these enzymes was developed, and their molecular masses were determined. The main catalytic properties of the studied enzymes (pH optimum and specificity to bacterial substrates) were found to be similar. Both enzymes lyse Escherichia coli cells like chicken egg lysozyme, but more efficiently lyse S. enteritidis cells and cannot lyse Micrococcus luteus, a good substrate for chicken egg lysozyme. Similar properties of exolysin and endolysin suggest that these enzymes are structurally similar or even identical.

Use of a reverse micelle system for study of oligomeric structure of NAD+-reducing hydrogenase from Ralstonia eutropha H16.

Inclusion of an oligomeric enzyme, NAD+-dependent hydrogenase from the hydrogen-oxidizing bacterium Ralstonia eutropha, into a system of reverse micelles of different sizes resulted in its dissociation into catalytically active heterodimers and subunits, which were characterized in reactions with various substrates. It was found that: 1) the native tetrameric form of this enzyme catalyzes all types of studied reactions; 2) hydrogenase dimer, HoxHY, is a minimal structural unit catalyzing hydrogenase reaction with an artificial electron donor, reduced methyl viologen; 3) all structural fragments containing FMN and NAD+/NADH-binding sites exhibit catalytic activity in diaphorase reactions with one- and two-electron acceptors; 4) small subunits, HoxY and HoxU also exhibit activity in diaphorase reactions with artificial acceptors. These results can be considered as indirect evidence that the second FMN molecule may be associated with one of the small subunits (HoxY or HoxU) of the hydrogenase from R. eutropha.

Laccases from Basidiomycetes: physicochemical characteristics and substrate specificity towards methoxyphenolic compounds.

Laccases from the Basidiomycetes Coriolus hirsutus, Coriolus zonatus, Cerrena maxima, and Coriolisimus fulvocinerea have been isolated and purified to homogeneity and partially characterized. The kinetics of oxidation of different methoxyphenolic compounds by the fungal laccases has been studied. As laccase substrates, such methoxyphenolic compounds as 4-hydroxy-3,5-dimethoxycinnamic acid (sinapinic acid), 4-hydroxy-3-methoxycinnamic acid (ferulic acid), and 2-methoxyphenol (guaiacol) were used. The stoichiometries of the enzymatic reactions were determined: guaiacol and sinapinic acid are one-electron donors and their oxidation apparently results in the formation of dimers. It was established that kcat/Km, which indicates the effectiveness of catalysis, increases in the series guaiacol, ferulic acid, and sinapinic acid. This fact might be connected with the influence of substituents of the phenolic ring of the substrates. This phenomenon was established for fungal laccases with different physicochemical properties, amino acid composition, and carbohydrate content. This suggests that all fungal laccases possess the same mechanism of interaction between organic substrate electron donors and the copper-containing active site of the enzyme and that this interaction determines the observed values of the kinetic parameters.

Fluorescence dynamics of green fluorescent protein in AOT reversed micelles.

We have used the enhanced green fluorescent protein (EGFP) to investigate the properties of surfactant-entrapped water pools in organic solvents (reversed micelles) with steady-state and time-resolved fluorescence methods. The surfactant used was sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and the organic solvents were isooctane and (the more viscous) dodecane, respectively. The water content of the water pools could be controlled through the parameter w0, which is the water-to-surfactant molar ratio. With steady-state fluorescence, it was observed that subtle fluorescence changes could be noted in reversed micelles of different water contents. EGFP can be used as a pH-indicator of the water droplets in reversed micelles. Time-resolved fluorescence methods also revealed subtle changes in fluorescence decay times when the results in bulk water were compared with those in reversed micelles. The average fluorescence lifetimes of EGFP scaled with the relative fluorescence intensities. Time-resolved fluorescence anisotropy of EGFP in aqueous solution and reversed micelles yielded single rotational correlation times. Geometrical considerations could assign the observed correlation times to dehydrated protein at low w0 and internal EGFP rotation within the droplet at the highest w0.

Structural organization of membrane and soluble forms of somatic angiotensin-converting enzyme.

The catalytic activity and quaternary structure of soluble (s) and membrane (m) forms of angiotensin-converting enzyme (ACE) were studied in reversed micelles of ternary system Aerosol OT--water--octane. The profile of the dependence of the catalytic activity of the two enzyme forms on the degree of surfactant hydration (micellar size) had several optima corresponding to the function of various active oligomeric enzyme forms; the curves for the s- and m-forms of ACE were different. Data of sedimentation analysis prove that in reversed micelles, s-ACE can exist as monomers, dimers, or tetramers depending on the hydration degree, and the m-form is present as dimers and tetramers only. The values of the kinetic parameters for the hydrolysis of the substrate furylacryloyl-Phe-Gly-Gly by all the enzyme forms were determined, and the data indicate that the activity of the m-form is enhanced by oligomerization. The ACE activity strongly depends on the medium; it is higher when ACE is in contact with matrix or other enzyme molecules.

Pressure regulation of malic dehydrogenase in reversed micelles.

Malic dehydrogenase (MDH) studied in water and reversed micelles upon pressure application revealed a difference in catalysis. Whereas MDH in water appeared to be not sensitive to the pressure increasing, the catalytic activity of MDH in reversed micelles showed bell-shaped dependencies both on pressure and surfactant hydration degree, w0. The catalytic activity of MDH was found to be maximal under moderate pressure equal to 300-500 bar and at w0 approximately 14 with the difference between lowest and highest levels of the catalytic activity amounted to about 10 times. The work presented demonstrates for the first time the co-operative effect of reversed micelles and pressure application to malic dehydrogenase leading to the enzyme regulation that cannot be realized in aqueous solution.

Catalytically active monomers of E. coli glyceraldehyde-3-phosphate dehydrogenase.

Monomeric forms of E. coli glyceraldehyde-3-phosphate dehydrogenase have been prepared using two different experimental approaches: (1) covalent immobilization of a tetramer on a solid support via a single subunit with subsequent dissociation of non-covalently bound subunits in the presence of urea, and (2) entrapment of monomeric species into reversed micelles of Aerosol OT in octane. Isolated monomers were shown to be catalytically active, exhibiting KM values close to the parameters characteristic of the tetrameric forms. Like tetramers, isolated monomers did not use NADP7 as a coenzyme.

Thermobarostability of alpha-chymotrypsin in reversed micelles of aerosol OT in octane solvated by water-glycerol mixtures.

Thermostability of alpha-chymotrypsin at normal pressure in reversed micelles depends on both an effective surfactant solvation degree and glycerol content in the system. The difference in alpha-chymotrypsin stability in reversed micelles at various glycerol concentrations [up to 60% (v/v)] was more pronounced at high surfactant degrees of solvation, R >/= 16. After a 1-h incubation at 40 degrees C in "aqueous" reversed micelles (in the absence of glycerol), alpha-chymotrypsin retained only 1% of initial catalytic activity and 10, 22, 59, and 48% residual activity in glycerol-solvated micelles with 20, 30, 50, and 60% (v/v) glycerol, respectively. The explanation of the observed effects is given in the frames of micellar matrix structural order increasing in the presence of glycerol as a water-miscible cosolvent that leads to the decreasing mobility of the alpha-chymotrypsin molecule and, thus the increase of its stability. It was found that glycerol or hydrostatic pressure could be used to stabilize alpha-chymotrypsin in reversed micelles; a lower pressure is necessary to reach a given level of enzyme stability in the presence of glycerol.

Formation of homo- and heterooligomeric supramolecular structures by D-glyceraldehyde-3-phosphate dehydrogenase and lactate dehydrogenase in reversed micelles of aerosol OT in octane.

The supramolecular structure of oligomeric enzymes can be specifically regulated by changing the size of an inner cavity of Aerosol OT reversed micelles in octane. Both D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and lactate dehydrogenase (LDH) reveal an ability to exist and function in monomeric, dimeric and tetrameric forms (homooligomers). Various heterooligomeric complexes, in particular, GAPDH monomer--LDH monomer, GAPDH dimer--LDH tetramer were detected in reversed micelles.

Stability and stabilization of recombinant peroxidase in reversed micelles.

Stability of recombinant peroxidase lacking carbohydrate residues on the surface of the protein molecule has been characterized in reversed micelles of Aerosol OT in octane. The enzyme stability was found to depend on the surfactant hydration degree (w0 = [H2O]/[AOT]). Residual activity after 1 h incubation dropped to zero at w0 = 7 but was 54% at w0 = 25. However, the residual activity levels at all values of hydration degree were definitely low compared to that of glycosylated wild-type horseradish peroxidase. The stability of the enzyme apparently depends on the presence of carbohydrate residues. Stabilization of recombinant peroxidase in reversed micellar system involved sugar-containing co-surfactants such as Tweens and Spans is proposed. As an example, addition of 1 mM Span 80 (1% relative to AOT concentration) increased the recombinant peroxidase stability up to that of wild-type peroxidase.

Formation and properties of dimeric recombinant horseradish peroxidase in a system of reversed micelles.

Wild-type recombinant horseradish peroxidase purified and refolded from Escherichia coli inclusion bodies has been studied in the system of bis(2-ethylhexyl)sulphosuccinate sodium salt (Aerosol OT)-reversed micelles in octane. In contrast with native horseradish peroxidase the wild-type recombinant enzyme forms dimeric structures as judged by sedimentation analysis. Peroxidase substrates affect the equilibrium between monomeric and dimeric enzyme forms. The dependence of the catalytic activity of recombinant peroxidase on the degree of hydration of the surfactant exhibits two maxima with pyrogallol, o-phenylene- diamine, guaiacol and o-dianisidine, with different ratios of activities for the first and second maxima. The differences in activities of monomeric and dimeric forms of the recombinant horseradish peroxidase provide evidence for active-site screening in dimeric forms. This has been used to model a dimeric structure of recombinant horseradish peroxidase with the screened entrance to the active site. In the model structure obtained, three of eight glycosylation sites were screened. This might explain the absence of dimeric structures in native enzyme peroxidase. The system of reversed micelles provides, for the first time, evidence for the formation of dimeric structures by recombinant plant peroxidase with an altered substrate specificity compared with the native enzyme. Thus one can assume that haem-containing peroxidases in general are able to form dimeric structures.

Formate dehydrogenase in a reversed micelle system: regulation of catalytic activity and oligomeric composition of the enzyme.

Formate dehydrogenases from the methylotrophic bacteria Pseudomonas sp. 101 and Mycobacterium vaccae N10 were studied in a system of Aerosol OT reversed micelles in octane. Three peaks of the catalytic activity were found on the plot of activity versus surfactant hydration degree (the size of the micellar inner cavity) which corresponded to functions of the enzyme in various oligomeric forms: monomeric, dimeric, and octameric. Kinetic data were confirmed by results of sedimentation analysis. The enzyme was chemically modified by a bifunctional reagent (dimethyl suberimidate) to obtain a catalytically active non-dissociating dimeric molecule of formate dehydrogenase. In the case of the covalently-linked non-dissociating dimeric enzyme, the peak which corresponded to the monomeric form of the enzyme was found to disappear from the catalytic activity curve.

Dimerization of recombinant horseradish peroxidase in a reversed micellar system.

Recombinant horseradish peroxidase reactivated from E. coli inclusion bodies was studied in a reversed micellar system of AOT in octane. The ability of the recombinant enzyme, in contrast to native horseradish peroxidase, to form a dimeric structure was found. The existence of the dimer was proved by results of sedimentation analysis. Dimer/monomer ratio in the enzyme-containing micelles and dimer catalytic activity were found to depend on the substrate used (pyrogallol, guaiacol, o-dianisidine, o-phenylenediamine). Computer modelling was used to describe possible structures of the dimeric recombinant horseradish peroxidase.

High-pressure stabilization of alpha-chymotrypsin entrapped in reversed micelles of aerosol OT in octane against thermal inactivation.

alpha-Chymotrypsin (CT) solubilized in reversed micelles of sodium bis-(2-ethylhexyl)-sulfosuccinate (AOT) undergoes thermal inactivation and the enzyme stability decreases significantly when temperature increases (25-40 degrees C). The half-life of CT in micelles shows a bell-shaped dependence on the degree of hydration of AOT (wo) analogous to the previously obtained dependence on wo for the enzyme activity. The optima of catalytic activity and thermal stability have been observed under conditions where the diameter of the inner aqueous cavity of the micelle is close to the size of the enzyme molecule (wo = 10). Application of high hydrostatic pressure in the range of 1-1500 atm (bar) stabilizes CT against thermal inactivation at all hydration degrees (wo) from 7 to 20; the stabilization effect is most pronounced under the experimental conditions being far from the optimum for catalytic activity.

Lectin-like center in the molecule of alpha-chymotrypsin: formation of complexes with peroxidase and artificially glycosylated alpha-chymotrypsin.

Using the system of reversed micelles of Aerosol OT1 in octane as an instrument revealing the possibility of supramolecular structures formation, we have shown that the native alpha-chymotrypsin can form complexes with glycoproteins. Dimers of the native alpha-chymotrypsin with the artificially glycosylated one and with horseradish peroxidase (natural glycoprotein) were obtained. The position of the optimum on the dependence of the catalytic activity upon the hydration degree confirms the compact organization of the formed complexes. The ability of alpha-chymotrypsin to form such kind of complexes seems to play a key role in its absorption on glycocalix in vivo.

Revealing active site on the light subunit of penicillin acylase.

Serine-specific irreversible inhibitor phenylmethanesulfonyl fluoride (PMSF) inactivates penicillin acylase subunits, which were chromatographically separated under denaturing conditions and refolded by dialysis, in aqueous solution and Aerosol OT reversed micelles. The activities of both alpha and beta subunits decrease with increasing PMSF concentration but the dependence is no longer linear, in contrast with the native enzyme. The enzyme inactivated in aqueous solution, when solubilized in the micellar system at Wo = 12, exhibits an additional activity, which can be further inhibited by PMSF.