High temperature peroxidase activities of HRP and hemoglobin in the galleries of layered Zr(IV)phosphate

Determination of the total antioxidant capacity of the Chinese tea based on a novel "peroxidase/zirconium phosphonate"composite electrochemical sensor

In this work, a novel zirconium phosphonate (ZrPR1R2) was prepared by decorating both the aminoethoxy- group (R1) and the carboxypropyl- group (R2) on the zirconium phosphate layers in order to manipulate further the immobilization of the peroxidase (POD), and an antioxidant biosensor with higher sensitivity was constructed by dropping the POD/ZrPR1R2 composite onto the glassy carbon electrode surface. The activity of the POD/ZrPR1R2 composite was detected by Uv-vis spectra. The direct electrochemical behavior, the electrocatalytic response to dissolved oxygen and hydrogen peroxide, as well as the ability to detect total antioxidant capacity in tea sample were investigated by the methods of cyclic voltammetry. The results indicated that the immobilization of POD in ZrPR1R2 nanosheets matrix enhanced the enzymatic activity, and achieved the fast and direct electron transfer between POD and glassy carbon electrode. Moreover, the POD/ZrPR1R2 composite modified electrode show the electrocatalytic response to hydrogen peroxide in the linear range of 8.8×10-8 to 8.8×10-7 mol L-1, with the detection limit of 3.3×10-8 mol L-1. Attributing to the sensitive response to dissolved oxygen, the total antioxidant capacity can be detected directly in the real tea water by this POD/ZrPR1R2 composite modified electrode.

Development of enzyme/titanate nanosheet complex coated with molecularly imprinted polydopamine for colorimetric quercetin assay

A novel hybrid material, which is an enzyme/inorganic nanosheet complex coated by molecularly imprinted polymer (MIP), was developed, and applied to colorimetric quercetin assay. First, an enzyme/inorganic nanosheet complex was prepared from horseradish peroxidase (HRP) enzyme and titanate nanosheet (TiOx), using electrostatic interactions between them in acetate buffer. In the next place, dopamine self-polymerization was performed in the presence of HRP/TiOx complex with quercetin as a template, to prepare MIP membrane onto the HRP/TiOx complex. After washing process, a new hybrid material, MIP-coated HRP/TiOx complex (MIP-HT) was obtained. MIP-HT adsorbed quercetin efficiently, compared with NIP-HT that is an HRP/TiOx complex coated with non-imprinted polydopamine. MIP-HT showed enzymatic activity for an oxidation reaction of guaiacol, which is a chromogenic substrate of HRP, whereas the enzymatic activity of NIP-HT was significantly suppressed. The amount of brown product, formed by the color reaction, reduced owing to the presence of quercetin in sample solution, and a good liner relationship was observed between the concentration of quercetin and the increment of absorbance at 470 nm. The investigation using several biomolecules indicates that MIP-HT has the ability to detect quercetin and its analogues with selectivity. Therefore, MIP-HT shows great promise as a new and attractive material for use in colorimetric assay of quercetin or quercetin analogues.

Unique Enzyme Activity of Peroxidase on a Clay Nanosheet

The adsorption behavior and enzyme activity of horseradish peroxidase (HRP) was examined on a synthetic clay nanosheet, whose surface is flat at the atomic level and is negatively charged. The results showed that HRP is adsorbed effectively (adsorption equilibrium constant, K = 1.61 × 10⁷ L mol^-1) and that the structure of HRP was altered on the clay surface. The enzyme activity of HRP on the clay surface was evaluated by using H₂O₂ and tert-BuOOH as a substrate. As a result, HRP on the clay surface was able to work for tert-BuOOH, while HRP in solution did not show any activity. In addition, HRP on SSA showed reactivity even under the high-temperature conditions. These results indicate that the clay nanosheet can be a unique modifier for enzyme activity of HRP.

Rationally Designed, "Stable-on-the-Table" NanoBiocatalysts Bound to Zr(IV) Phosphate Nanosheets

Rational approaches for the control of nano-bio interfaces for enzyme stabilization are vital for engineering advanced, functional nanobiocatalysts, biosensors, implants, or "smart" drug delivery systems. This chapter presents an overview of our recent efforts on structural, functional, and mechanistic details of enzyme nanomaterials design, and describes how progress is being made by hypothesis-driven rational approaches. Interactions of a number of enzymes having wide ranges of surface charges, sizes, and functional groups with α-Zr(IV)phosphate (α-ZrP) nanosheets are carefully controlled to achieve high enzyme binding affinities, excellent loadings, significant retention of the bound enzyme structure, and high enzymatic activities. In specific cases, catalytic activities and selectivities of the nanobiocatalysts are improved over those of the corresponding pristine enzymes. Maximal enzyme structure retention has been obtained by coating the nanosheets with appropriate proteinaceous materials to soften the enzyme-nanosheet interface. These systematic manipulations are of significant importance to understand the complex behavior of enzymes at inorganic surfaces.

Synergistic Functions of Enzymes Bound to Semiconducting Layers

Synthesis and cooperative functions of hybrid materials composed of enzyme and semiconducting layers are described in this chapter. The hybrids were produced via a simple physical interaction between the components, that is, electrostatic interaction in an aqueous solution. To form interstratifying enzymes in the galleries, solution pH, which is a key parameter to decide surface potential, should be adjusted appropriately. In other words, enzymes should have an opposite charge when compared to that of the layers at an identical pH. Even though the intercalation slightly reduced enzymatic activity as compared to those of the free enzymes, stability under cruel conditions was drastically improved due to screening effect of semiconducting layers from extrinsic stimuli. In addition, photochemical control of redox enzymes sandwiched between semiconducting layers was accomplished. Light irradiation of the hybrids induced band gap excitation of the layers, and holes produced in the valence band activated the enzymes. It was revealed that the semiconducting layers with magnetic elements might be useful to magnetic application (separation) of enzymes as similar to conventional magnetic beads.

Fe-doped CeO2 nanorods for enhanced peroxidase-like activity and their application towards glucose detection

Surface defects of Fe-doped CeO₂ nanorods were found to be active sites for increasing peroxidase mimetic activity.

Rational Design of Nanoparticle Platforms for "Cutting-the-Fat": Covalent Immobilization of Lipase, Glycerol Kinase, and Glycerol-3-Phosphate Oxidase on Metal Nanoparticles

The aggregates of nanoparticles (NPs) are considered better supports for the immobilization of enzymes, as these promote enzyme kinetics, due to their unusual but favorable properties such as larger surface area to volume ratio, high catalytic efficiency of certain immobilized enzymes, non-toxicity of some of the nanoparticle matrices, high stability, strong adsorption of the enzyme of interest by a number of different approaches, and faster electron transportability. Co-immobilization of multiple enzymes required for a multistep reaction cascade on a single support is more efficient than separately immobilizing the corresponding enzymes and mixing them physically, since products of one enzyme could serve as reactants for another. These products can diffuse much more easily between enzymes on the same particle than diffusion from one particle to the next, in the reaction medium. Thus, co-immobilization of enzymes onto NP aggregates is expected to produce faster kinetics than their individual immobilizations on separate matrices. Lipase, glycerol kinase, and glycerol-3-phosphate oxidase are required for lipid analysis in a cascade reaction, and we describe the co-immobilization of these three enzymes on nanocomposites of zinc oxide nanoparticles (ZnONPs)-chitosan (CHIT) and gold nanoparticles-polypyrrole-polyindole carboxylic acid (AuPPy-Pin5COOH) which are electrodeposited on Pt and Au electrodes, respectively. The kinetic properties and analytes used for amperometric determination of TG are fully described for others to practice in a trained laboratory. Cyclic voltammetry, scanning electron microscopy, Fourier transform infra-red spectra, and electrochemical impedance spectra confirmed their covalent co-immobilization onto electrode surfaces through glutaraldehyde coupling on CHIT-ZnONPs and amide bonding on AuPPy/Pin5COOH. The combined activities of co-immobilized enzymes was tested amperometrically, and these composite nanobiocatalysts showed optimum activity within 4-5s, at pH 6.5-7.5 and 35°C, when polarized at a potential between 0.1 and 0.4V. Co-immobilized enzymes showed excellent linearity within 50-700mg/dl of the lipid with detection limit of 20mg/dl for triolein. The half life of co-immobilized enzymes was 7 months, when stored dry at 4°C which is very convenient for practical applications. Co-immobilized biocatalysts measured triglycerides in the sera of apparently healthy persons and persons suffering from hypertriglyceridemia, which is recognized as a leading cause for heart disease. The measurement of serum TG by co-immobilized enzymes was unaffected by the presence of a number of serum substances, tested as potential interferences. Thus, co-immobilization of enzymes onto aggregates of NPs resulted in improved performance for TG analysis.

"Stable-on-the-Table" Biosensors: Hemoglobin-Poly (Acrylic Acid) Nanogel BioElectrodes with High Thermal Stability and Enhanced Electroactivity

In our efforts toward producing environmentally responsible but highly stable bioelectrodes with high electroactivities, we report here a simple, inexpensive, autoclavable high sensitivity biosensor based on enzyme-polymer nanogels. Met-hemoglobin (Hb) is stabilized by wrapping it in high molecular weight poly(acrylic acid) (PAA, M_W 450k), and the resulting nanogels abbreviated as Hb-PAA-450k, withstood exposure to high temperatures for extended periods under steam sterilization conditions (122 °C, 10 min, 17–20 psi) without loss of Hb structure or its peroxidase-like activities. The bioelectrodes prepared by coating Hb-PAA-450k nanogels on glassy carbon showed well-defined quasi-reversible redox peaks at −0.279 and −0.334 V in cyclic voltammetry (CV) and retained >95% electroactivity after storing for 14 days at room temperature. Similarly, the bioelectrode showed ~90% retention in electrochemical properties after autoclaving under steam sterilization conditions. The ultra stable bioelectrode was used to detect hydrogen peroxide and demonstrated an excellent detection limit of 0.5 μM, the best among the Hb-based electrochemical biosensors. This is the first electrochemical demonstration of steam-sterilizable, storable, modular bioelectrode that undergoes reversible-thermal denaturation and retains electroactivity for protein based electrochemical applications.

Enzyme-mimetic activity of Ce-intercalated titanate nanosheets

Colloidal solutions of Ce-doped titanate nanosheets (Ce-TNS) with tiny dimensions (<10 nm) were fabricated through a hydrolysis reaction of titanium tetraisopropoxide and Ce(NO3)3, and their annihilation activity for reactive oxygen species (ROS) was investigated. The obtained Ce-TNS had an akin crystal structure to layered tetratitanate (Ti4O9(2-)) and Ce ions occupied interlayer space between the host layers with a negative charge. The Ce-TNS possessed a superoxide dismutase (SOD) mimetic activity for disproportionation of superoxide anion radicals (O2(-)) as target ROS. It was explained that the annihilation of O2(-) caused a valence fluctuation of Ce ions existing in the interlayer. Moreover, the activity of Ce-TNS exceeded that of CeO2 nanoparticles recently attracting much attention as an inorganic SOD mimic. The superior performance was explained mainly by a high dispersion stability of the Ce-TNS bringing about a huge reaction area. Moreover, the Ce-TNS protected DNA molecules from ultraviolet light induced oxidative damage, demonstrating effectiveness as one of the new inorganic protecting agents for biomolecules and tissues.

Enhanced catalytic activity of enzymes interacting with nanometric titanate nanosheets

Enzymatic activity of horseradish peroxidase (HRP) at diluted conditions is highly increased under the presence of nanometric titanate nanosheets (TNS).

Efficient biocatalysis in organic media with hemoglobin and poly(acrylic acid) nanogels

We previously reported that the stability and aqueous catalytic activity of met-hemoglobin (Hb) was improved when covalently conjugated with poly(acrylic acid) (PAA). In the current study, the Hb-PAA-water interface was modified to improve Hb catalytic efficiency in organic solvents (0-80% v/v organic solvent; remainder is the conjugate, the substrate, and water). The protein-polymer-solvent interface modification was achieved by esterifying the carboxylic acid groups of Hb-PAA with ethanol (EtOH) or 1-propanol (1-prop) after activation with carbodiimide. The resulting esters (Hb-PAA-Eth and Hb-PAA-1-prop, respectively) showed high peroxidase-like catalytic activities in acetonitrile (ACN), dimethylformamide (DMF), EtOH, and methanol (MeOH). Catalytic activities depended on the log(P) values of the solvents, which is a measure of solvent lipophilicity. The highest weighted-average activities were noted in MeOH for all three conjugates, and the lowest average activities were noted in DMF for two of the conjugates. Interestingly, the average activities of the conjugates were higher than that of Hb in all solvents except in ACN. The ratio of the catalytic rate constant (kcat) to the Michaelis constant (KM), the catalytic efficiency, for Hb-PAA-Eth in MeOH was the highest noted, and it is ~3-fold higher than that of Hb in buffer; conjugates offered higher efficiencies than Hb at most solvent compositions. This is the very first general, versatile, modular strategy of coupling the enhanced stability of Hb with improved activity in organic solvents via the chemical manipulation of the polymer shell around Hb and provides a robust approach to efficient biocatalysis in organic solvents.

Function, structure, and stability of enzymes confined in agarose gels

Research over the past few decades has attempted to answer how proteins behave in molecularly confined or crowded environments when compared to dilute buffer solutions. This information is vital to understanding in vivo protein behavior, as the average spacing between macromolecules in the cell cytosol is much smaller than the size of the macromolecules themselves. In our study, we attempt to address this question using three structurally and functionally different model enzymes encapsulated in agarose gels of different porosities. Our studies reveal that under standard buffer conditions, the initial reaction rates of the agarose-encapsulated enzymes are lower than that of the solution phase enzymes. However, the encapsulated enzymes retain a higher percentage of their activity in the presence of denaturants. Moreover, the concentration of agarose used for encapsulation had a significant effect on the enzyme functional stability; enzymes encapsulated in higher percentages of agarose were more stable than the enzymes encapsulated in lower percentages of agarose. Similar results were observed through structural measurements of enzyme denaturation using an 8-anilinonaphthalene-1-sulfonic acid fluorescence assay. Our work demonstrates the utility of hydrogels to study protein behavior in highly confined environments similar to those present in vivo; furthermore, the enhanced stability of gel-encapsulated enzymes may find use in the delivery of therapeutic proteins, as well as the design of novel strategies for biohybrid medical devices.

Tuning the activities and structures of enzymes bound to graphene oxide with a protein glue

Graphene oxide (GO) is being investigated extensively for enzyme and protein binding, but many enzymes bound to GO denature considerably and lose most of their activities. A simple, novel, and efficient approach is described here for improving the structures and activities of enzymes bound to GO such that bound enzymes are nearly as active as those of the corresponding unbound enzymes. Our strategy is to preadsorb highly cationized bovine serum albumin (cBSA) to passivate GO, and cBSA/GO (bGO) served as an excellent platform for enzyme binding. The binding of met-hemoglobin, glucose oxidase, horseradish peroxidase, BSA, catalase, lysozyme, and cytochrome c indicated improved binding, structure retention, and activities. Nearly 100% of native-like structures of all the seven proteins/enzymes were noted at near monolayer formation of cBSA on GO (400% w/w), and all bound enzymes indicated 100% retention of their activities. A facile, benign, simple, and general method has been developed for the biofunctionalization of GO, and this approach of coating with suitable protein glues expands the utility of GO as an advanced biophilic nanomaterial for applications in catalysis, sensing, and biomedicine.

Nanobio interfaces: charge control of enzyme/inorganic interfaces for advanced biocatalysis

Specific approaches to the rational design of nanobio interfaces for enzyme and protein binding to nanomaterials are vital for engineering advanced, functional nanobiomaterials for biocatalysis, sensing, and biomedical applications. This feature article presents an overview of our recent discoveries on structural, functional, and mechanistic details of how enzymes interact with inorganic nanomaterials and how they can be controlled in a systematic manner using α-Zr(IV)phosphate (α-ZrP) as a model system. The interactions of a number of enzymes having a wide array of surface charges, sizes, and functional groups are investigated. Interactions are carefully controlled to screen unfavorable repulsions and enhance favorable interactions for high affinity, structure retention, and activity preservation. In specific cases, catalytic activities and substrate selectivities are improved over those of the pristine enzymes, and two examples of high activity near the boiling point of water have been demonstrated. Isothermal titration calorimetric studies indicated that enzyme binding is coupled to ion sequestration or release to or from the nanobio interface, and binding is controlled in a rational manner. We learned that (1) bound enzyme stabilities are improved by lowering the entropy of the denatured state; (2) maximal loadings are obtained by matching charge footprints of the enzyme and the nanomaterial surface; (3) binding affinities are improved by ion sequestration at the nanobio interface; and (4) maximal enzyme structure retention is obtained by biophilizing the nanobio interface with protein glues. The chemical and physical manipulations of the nanobio interface are significant not only for understanding the complex behaviors of enzymes at biological interfaces but also for desiging better functional nanobiomaterials for a wide variety of practical applications.

Control of enzyme-solid interactions via chemical modification

Electrostatic forces could contribute significantly toward enzyme-solid interactions, and controlling these charge-charge interactions while maintaining high affinity, benign adsorption of enzymes on solids is a challenge. Here, we demonstrate that chemical modification of the surface carboxyl groups of enzymes can be used to adjust the net charge of the enzyme and control binding affinities to solid surfaces. Negatively charged nanosolid, α-Zr(HPO(4))(2)·H(2)O (abbreviated as α-ZrP) and two negatively charged proteins, glucose oxidase (GO) and methemoglobin (Hb), have been chosen as model systems. A limited number of the aspartate and glutamate side chains of these proteins are covalently modified with tetraethylenepentamine (TEPA) to convert these negatively charged proteins into the corresponding positively charged ones (cationized). Cationized proteins retained their structure and activities to a significant extent, and the influence of cationization on binding affinities has been tested. Cationized GO, for example, showed 250-fold increase in affinity for the negatively charged α-ZrP, when compared to that of the unmodified GO, and cationized Hb, similarly, indicated 26-fold increase in affinity. Circular dichroism spectra showed that α-ZrP-bound cationized GO retained native-like structure to a significant extent, and activity studies showed that cationized GO/α-ZrP complex is ~2.5-fold more active than GO/α-ZrP. Cationized Hb/α-ZrP retained ~75% of activity of Hb/α-ZrP. Therefore, enzyme cationization enhanced affinities by 1-2 orders of magnitude, while retaining considerable activity for the bound biocatalyst. This benign, chemical control over enzyme charge provided a powerful new strategy to rationally modulate enzyme-solid interactions while retaining their biocatalytic properties.

Fabrication of functional bioinorganic nanoconstructs by polymer-silica wrapping of individual myoglobin molecules

Discrete core-shell hybrid nanoparticles comprising individual met-myoglobin (met-Mb) molecules incarcerated within an ultrathin polymer/silica shell were prepared without loss of biofunctionality by a facile self-assembly procedure. Solubilisation of met-Mb in cyclohexane in the near-absence of water was achieved by wrapping individual protein molecules in the amphiphilic triblock copolymer poly(ethylene-oxide)19-poly(propylene-oxide)69-poly(ethylene-oxide)19 (EO19-PO69-EO19, P123). Addition of tetramethoxysilane to the met-Mb/P123 conjugates in cyclohexane produced discrete nanoparticles that contained protein, polymer and silica, and which were 3-5.5 nm in size, consistent with the entrapment of single molecules of met-Mb. The hybrid nanoconstructs were isolated and re-dispersed in water without loss of secondary structure, and remained functionally active with respect to redox reactions and CO and O2 ligand binding at the porphyrin metallocentre. The incarcerated met-Mb biomolecules showed enhanced thermal stability up to a temperature of around 85 °C. These properties, along with the high biocompatibility of silica and P123, suggest that the silicified protein-polymer constructs could be utilised as functional nanoscale components in bionanotechnology.

A novel mediator-free biosensor based on co-intercalation of DNA and hemoglobin in the interlayer galleries of alpha-zirconium phosphate

A novel mediator-free biosensor was constructed by the co-intercalation of negatively charged DNA and positively charged hemoglobin (Hb) in the interlayer galleries of layered alpha-zirconium phosphate (alpha-ZrP) with the delamination-assembly procedure at pH 5.5. X-ray diffraction and field-emission scanning electron microscopy results revealed the featured layered structure for the re-assembled DNA/Hb/alpha-ZrP composite. Infrared spectroscopy and circular dichroism results confirmed the coexistence of Hb and DNA in the composite and the considerably retained protein conformation of intercalated Hb. The direct electron transfer of Hb was facilitated by the co-intercalation of DNA and Hb. Because of the synergistic effect of alpha-ZrP host and co-intercalated DNA guest, the DNA/Hb/alpha-ZrP modified electrode exhibited good electrocatalytic response to H(2)O(2) with higher sensitivity of 0.79 A M(-1) cm(-2) and lower detection of 4.28x10(-7) M in the linear range of 7.28x10(-7) to 9.71x10(-5) M. Furthermore, the electrocatalytic activity of Hb in the DNA/Hb/alpha-ZrP composite retained at high temperature (85 degrees C) or in the presence of organic solvent (CH(3)CN), which could be the protection of alpha-ZrP nanosheets.

Molecular signatures of enzyme-solid interactions: thermodynamics of protein binding to alpha-Zr(IV) phosphate nanoplates

Isothermal titration calorimetry (ITC) was used to determine the thermodynamics of protein binding to the nanoplates of alpha-Zr(HPO4)2.H2O (alpha-ZrP). The binding constants (K(b)) and DeltaG, DeltaH, and DeltaS have been evaluated for a small set of proteins, and K(b) values are in the range of 2-760 x 10(5) M(-1). The binding of positively charged proteins to the negatively charged alpha-ZrP was endothermic, while the binding of negatively charged proteins was exothermic, and these are contrary to expectations based on a simple electrostatic model. The binding enthalpies of the proteins varied over a range of -24 to +25 kcal/mol, and these correlated roughly with the net charge on the protein (R2 = 0.964) but not with other properties such as the number of basic residues, polar residues, isoelectric point, surface area, or molecular mass. Linear fits to the enthalpy plots indicated that each charge on the protein contributes 1.18 kcal/mol toward the binding enthalpy. Binding entropies of positively charged proteins were favorable (>0) while the binding entropies of negatively charged proteins were unfavorable (<0). The DeltaS values varied over a range of -51 to +98 cal/mol x K, and these correlated very well with the net charge on the protein (R2 = 0.999), but DeltaS is in the opposite direction of DeltaH. The binding or release of cations to/from the protein-solid interface can account for these observations. There was no correlation between the binding free energy (DeltaG(obs)) and any specific molecular properties, but it is likely to be a sum of several opposing interactions of large magnitudes. For the first time, the binding enthalpies and entropies are connected to specific molecular properties. The model suggests that the thermodynamic parameters can be controlled by choosing appropriate cations or by adjusting the net charge on the protein. We hope that physical insights such as these will be useful in understanding the complex behavior of proteins at biological interfaces.

Protein-solid interactions: important role of solvent, ions, temperature, and buffer in protein binding to alpha-Zr(IV) phosphate

The interaction of proteins with a solid surface involves a complex set of interactions, and elucidating the details of these interactions is essential in the rational design of solid surfaces for applications in biosensors, biocatalysis, and biomedical applications. We examined the enthalpy changes accompanying the binding of met-hemoglobin, met-myoglobin, and lysozyme to layered alpha-Zr(IV)phosphate (20 mM NaPipes, 1 mM TBA, pH 7.2, 298 K) by titration calorimetry, under specific conditions. The corresponding binding enthalpies for the three proteins are -24.2 +/- 2.2, -10.6 +/- 2, and 6.2 +/- 0.2 kcal/mol, respectively. The binding enthalpy depended on the charge of the protein where the binding of positively charged proteins to the negatively charged solid surface was endothermic while the binding of negatively charged proteins to the negatively charged solid was exothermic. These observations are contrary to a simple electrostatic model where binding to the oppositely charged surface is expected to be exothermic. The binding enthalpy depended on the net charge on the protein, ionic strength of the medium, the type of buffer ions present, and temperature. The temperature dependence studies of binding enthalpies resulted in the estimation of heat capacity changes accompanying the binding. The heat capacity changes observed with Hb, Mb, and lysozyme are 1.4 +/- 0.3, 0.89 +/- 0.2, and 0.74 +/- 0.1 kcal/(mol.K), respectively, and these values depended on the net charge of the protein. The enthalpy changes also depended linearly on the enthalpy of ionization of the buffer, and the numbers of protons released per protein estimated from this data are 12.6 +/- 2, 6.0 +/- 1.2, and 1.2 +/- 0.5 for Hb, Mb, and lysozyme, respectively. Binding enthalpies, independent of buffer ionization, are also estimated from these data. Entropy changes are related to the loss in the degrees of freedom when the protein binds to the solid and the displacement of solvent molecules/protons/ions from the protein-solid interface. Proton coupled protein binding is one of the major processes in these systems, which is novel, and the binding enthalpies can be predicted from the net charge of the protein, enthalpy of buffer ionization, ionic strength, and temperature.

Colloidal assembly of proteins with delaminated lamellas of layered metal hydroxide

The colloidal LDH nanosheets have been assembled in aqueous medium with three proteins having different structures and surface charge distributions. In addition to the interfacial adsorption features, the secondary and/or higher level structures of surface-bound proteins are investigated by ATR-FTIR and fluorescence spectroscopic techniques. The structure and conformation of porcine pancreatic lipase (PPL), for which the negative charges are concentrated on the side surface opposite to active sites, are well retained, but the orientations of PPL molecules on two-dimensional LDH nanosheets could be lying flat or standing up depending on the PPL/LDH ratio. The bioactivity of PPL lying flat is enhanced in both the hydrolysis and kinetic resolution in comparison with its soluble counterpart. In the case of hemoglobin (Hb), a tetrameric hemeprotein with relatively uniform distribution of surface negative charges, the interfacial assembly might result in the unfolding of its tertiary or quaternary structure, but its secondary structure and redox-active heme groups are not denatured. Although the secondary structure of bovine serum albumin (BSA), for which the negative charges are distributed along the surfaces of linearly arranged domains I and II, is unfolded, the loss of the ordered structure is less than previously found owing to the less curvature of the two-dimensional LDH nanosheet surface. This is the first report related to the investigations of protein structures, conformations, and orientations in the biohybrids consisting of LDH nanosheets.

Thermostable biocatalytic films of enzymes and polylysine on electrodes and nanoparticles in microemulsions

Microemulsions of oil, water and surfactant were evaluated as media for biocatalysis at high temperatures employing films of polylysine (PLL) and the enzymes horseradish peroxidase (HRP), soybean peroxidase (SBP) and the protein myoglobin (Mb). PLL was covalently linked to oxidized pyrolytic graphite electrodes or carboxylated 500 nm diameter silica nanoparticles, then cross-linked by amidization to HRP, SBP and Mb. The resulting film systems were stable at 90 degrees C for >12 h in microemulsions. Characterization of the microemulsions by conductivity, viscosity and probe diffusion coefficients suggested that these media have bicontinuous microstructures from 25 to 90 degrees C. UV circular dichroism and visible spectroscopy confirmed that the enzymes retained near-native conformation in the films at temperatures as high as 90 degrees C. Oxidation of o-methoxyphenol to 3,3'-dimethoxy-4,4'-biphenoquinone by enzyme-PLL films on silica nanoparticles gave yields 3-5-fold larger in microemulsions at 90 degrees C compared to the same reaction at 25 degrees C. The best yields were in CTAB microemulsions and were 3-fold larger than in buffers at 90 degrees C.

Folding control and unfolding free energy of yeast iso-1-cytochrome c bound to layered zirconium phosphate materials monitored by surface plasmon resonance

The free energy change (Delta G degrees ) for the unfolding of immobilized yeast iso-1-cytochrome c (Cyt c) at nanoassemblies was measured by surface plasmon resonance (SPR) spectroscopy. Data show that SPR is sensitive to protein conformational changes, and protein solid interface exerts a major influence on bound protein stability. First, Cyt c was self-assembled on the Au film via the single thiol of Cys-102. Then, crystalline sheets of layered alpha-Zr(O(3)POH)(2).H(2)O (alpha-ZrP) or Zr(O(3)PCH(2)CH(2)COOH)(2).xH(2)O (alpha-ZrCEP) were adsorbed to construct alpha-ZrP/Cyt c/Au or alpha-ZrCEP/Cyt c/Au nanoassemblies. The construction of each layer was monitored by SPR, in real time, and the assemblies were further characterized by atomic force microscopy and electrochemical studies. Thermodynamic stability of the protein nanoassembly was assessed by urea-induced unfolding. Surprisingly, unfolding is reversible in all cases studied here. Stability of Cyt c in alpha-ZrP/Cyt c/Au increased by approximately 4.3 kJ/mol when compared to the unfolding free energy of Cyt c/Au assembly. In contrast, the protein stability decreased by approximately 1.5 kJ/mol for alpha-ZrCEP/Cyt c/Au layer. Thus, OH-decorated surfaces stabilized the protein whereas COOH-decorated surfaces destabilized it. These data quantitate the role of specific functional groups of the inorganic layers in controlling bound protein stability.

Improved Detection Limit and Stability of Amperometric Carbon Nanotube-Based Immunosensors by Crosslinking Antibodies with Polylysine

Amperometric immunosensor configurations featuring covalently bound anti-biotin antibodies (Ab) embedded into a polylysine (PLL)-single walled carbon nanotube (SWCNT) composite layer were evaluated. Assemblies were made by first oxidizing pyrolytic graphite (PG) electrodes to form surface carboxylic acid groups, to which PLL, SWCNTs and anti-biotin were covalently linked. Incorporating SWCNT into PLL-antibody assemblies improved the amperometric detection limit for biotin (Ag) labeled with horseradish peroxidase to 10 fmol mL(-1). Anti-biotin embedded into the PLL matrix had improved thermal stability and retained its binding ability for biotin after exposure to temperatures of 42 degrees C for up to 3 hours, while the noncrosslinked antibody was inactivated at this temperature in several minutes.

Endonuclease-like activity of heme proteins

Heme proteins, metmyoglobin, methemoglobin, and metcytochrome c showed unusual affinity for double-stranded DNA. Calorimetric studies show that binding of methemoglobin to calf thymus DNA (CTDNA) is weakly endothermic, and the binding constant is 4.9+/-0.7x10(5) M(-1). The Soret absorption bands of the heme proteins remained unchanged, in the presence of excess CTDNA, but a new circular dichroic band appeared at 210 nm. Helix melting studies indicated that the protein-DNA mixture denatures at a lower temperature than the individual components. Thermograms obtained by differential scanning calorimetry of the mixture indicated two distinct transitions, which are comparable to the thermograms obtained for individual components, but there was a reduction in the excess heat capacity. Activation of heme proteins by hydrogen peroxide resulted in the formation of high valent Fe(IV) oxo intermediates, and CTDNA reacted rapidly under these conditions. The rate was first-order in DNA concentration, and this reactivity resulted in DNA strand cleavage. Upon activation with hydrogen peroxide, for example, the heme proteins converted the supercoiled pUC18 DNA into nicked circular and linear DNA. No reaction occurred in the absence of the heme protein, or hydrogen peroxide. These data clearly indicate a novel property of several heme proteins, and this is first report of the endonuclease-like activity of the heme proteins.

Molecular modeling of the intercalation of porphyrins into α-zirconium phosphate

In this work, n-alkylamines (number of carbon atoms ranging from 3 to 10) were investigated in detail by molecular modeling as spacers for intercalating porphyrins into alpha-zirconium phosphate (alpha-ZrP). Pre-intercalated n-alkylamines can form either a flat monolayer or a canted bilayer in the gallery of alpha-ZrP. Based on the interlayer state and intercalative potential of the two modes in alpha-ZrP, it is suggested that the flat monolayer is a better spacer than the bilayer and that n-propylamine (PA) and n-butylamine (BA) in mobile monolayers are the best spacers among the n-alkylamines studied, as is also found experimentally. The intercalation behavior of TMPyP [5,10,15,20-tetrakis (1-methylpyridinium-4-yl) porphyrin] and several other porphyrins was investigated by calculating the intercalative potential. The calculated results showed that the porphyrins were densely packed in a canted monolayer model, and an increase of polarity of the substituent would facilitate the intercalation of the porphyrins.