Absorption spectra indicate conformational alteration of myoglobin adsorbed on polydimethylsiloxane

Oxidation-reduction imaging of myoglobin reveals two-phase oxidation in the reperfused myocardium

Myocardial infarction (MI) is a serious acute cardiovascular syndrome that causes myocardial injury due to blood flow obstruction to a specific myocardial area. Under ischemic-reperfusion settings, a burst of reactive oxygen species is generated, leading to redox imbalance that could be attributed to several molecules, including myoglobin. Myoglobin is dynamic and exhibits various oxidation-reduction states that have been an early subject of attention in the food industry, specifically for meat consumers. However, rarely if ever have the myoglobin optical properties been used to measure the severity of MI. In the current study, we develop a novel imaging pipeline that integrates tissue clearing, confocal and light sheet fluorescence microscopy, combined with imaging analysis, and processing tools to investigate and characterize the oxidation-reduction states of myoglobin in the ischemic area of the cleared myocardium post-MI. Using spectral imaging, we have characterized the endogenous fluorescence of the myocardium and demonstrated that it is partly composed by fluorescence of myoglobin. Under ischemia-reperfusion experimental settings, we report that the infarcted myocardium spectral signature is similar to that of oxidized myoglobin signal that peaks 3 h post-reperfusion and decreases with cardioprotection. The infarct size assessed by oxidation-reduction imaging at 3 h post-reperfusion was correlated to the one estimated with late gadolinium enhancement MRI at 24 h post-reperfusion. In conclusion, this original work suggests that the redox state of myoglobin can be used as a promising imaging biomarker for characterizing and estimating the size of the MI during early phases of reperfusion.

Plasma Treatment of PDMS for Microcontact Printing (μCP) of Lectins Decreases Silicone Transfer and Increases the Adhesion of Bladder Cancer Cells

The present study investigates silicone transfer occurring during microcontact printing (μCP) of lectins with polydimethylsiloxane (PDMS) stamps and its impact on the adhesion of cells. Static adhesion assays and single-cell force spectroscopy (SCFS) are used to compare adhesion of nonmalignant (HCV29) and cancer (HT1376) bladder cells, respectively, to high-affinity lectin layers (PHA-L and WGA, respectively) prepared by physical adsorption and μCP. The chemical composition of the μCP lectin patterns was monitored by time-of-flight secondary ion mass spectrometry (ToF-SIMS). We show that the amount of transferred silicone in the μCP process depends on the preprocessing of the PDMS stamps. It is revealed that silicone contamination within the patterned lectin layers inhibits the adhesion of bladder cells, and the work of adhesion is lower for μCP lectins than for drop-cast lectins. The binding capacity of microcontact printed lectins was larger when the PDMS stamps were treated with UV ozone plasma as compared to sonication in ethanol and deionized water. ToF-SIMS data show that ozone-based treatment of PDMS stamps used for μCP of lectin reduces the silicone contamination in the imprinting protocol regardless of stamp geometry (flat vs microstructured). The role of other possible contributors, such as the lectin conformation and organization of lectin layers, is also discussed.

Mechanistic Investigation of tert-Butanol's Impact on Biopharmaceutical Formulations: When Experiments Meet Molecular Dynamics

The use of tert-butyl alcohol for the lyophilization of pharmaceuticals has seen an uptick over the past years. Its advantages include increased solubility of hydrophobic drugs, enhanced product stability, shorter reconstitution time, and decreased processing time. While the mechanisms of protein stabilization exerted by cryo- and lyo-protectants are well known when water is the solvent of choice, little is known for organic solvents. This work investigates the interactions between two model proteins, namely, lactate dehydrogenase and myoglobin, and various excipients (mannitol, sucrose, 2-hydroxypropyl-β-cyclodextrin and Tween 80) in the presence of tert-butyl alcohol. We thermally characterized mixtures of these components by differential scanning calorimetry and freeze-drying microscopy. We also spectroscopically evaluated the protein recovery after freezing and freeze-drying. We additionally performed molecular dynamics simulations to elucidate the interactions in ternary mixtures of the herein-investigated excipients, tert-butyl alcohol and the proteins. Both experiments and simulations revealed that tert-butyl alcohol had a detrimental impact on the recovery of the two investigated proteins, and no combination of excipients yielded a satisfactory recovery when the organic solvent was present within the formulation. Simulations suggested that the denaturing effect of tert-butyl alcohol was related to its propensity to accumulate in the proximity of the peptide surface, especially near positively charged residues.

Analysis of the Site-Specific Myoglobin Modifications in the Melibiose-Derived Novel Advanced Glycation End-Product

MAGE (melibiose-derived advanced glycation end-product) is the glycation product generated in the reaction of a model protein with melibiose. The in vivo analog accumulates in several tissues; however, its origin still needs explanation. In vitro MAGE is efficiently generated under dry conditions in contrast to the reaction carried in an aqueous solvent. Using liquid chromatography coupled with mass spectrometry, we analyzed the physicochemical properties and structures of myoglobin glycated with melibiose under different conditions. The targeted peptide analysis identified structurally different AGEs, including crosslinking and non-crosslinking modifications associated with lysine, arginine, and histidine residues. Glycation in a dry state was more efficient in the formation of structures containing an intact melibiose moiety (21.9%) compared to glycation under aqueous conditions (15.6%). The difference was reflected in characteristic fluorescence that results from protein structural changes and impact on a heme group of the model myoglobin protein. Finally, our results suggest that the formation of in vitro MAGE adduct is initiated by coupling melibiose to a model myoglobin protein. It is confirmed by the identification of intact melibiose moieties. The intermediate glycation product can further rearrange towards more advanced structures, including cross-links. This process can contribute to a pool of AGEs accumulating locally in vivo and affecting tissue biology.

Reduced Washing Cycle for Sustainable Mackerel (Rastrelliger kanagurta) Surimi Production: Evaluation of Bio-Physico-Chemical, Rheological, and Gel-Forming Properties

Although dark muscle is currently the most important obstacle in marketing high-quality Indian mackerel (Rastrelliger kanagurta) surimi, reducing washing remains a challenge for long-term surimi production from this species. Herein, the impact of washing cycles (one (W1), two (W2), and three (W3) cycles) with a 1:3 mince to water ratio on the bio-physico-chemical properties, rheology, and gelling ability of mackerel surimi was evaluated. The yield, Ca2+-ATPase activity, TCA-soluble peptide, and myoglobin contents of surimi decreased as the number of washing cycles increased, while lipid removal, reactive SH content, and surface hydrophobicity of surimi increased. Surimi generated by W2 and W3 provided the same rheological patterns and Fourier-transform infrared spectroscopy (FTIR) spectra as unwashed mince, with the highest gel strength and whiteness, as well as the lowest expressible drip, thiobarbituric acid reactive substances (TBARS), and fishy odor. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated the presence of polymerized proteins stabilized by disulfide and other interactions. Using a scanning electron microscope, several concentrated dense areas and distributed pores generated by myofibrillar proteins gel networks were found. Surimi from W2 and W3 appeared to be of similar overall quality, however W2 had a larger yield. As a result of the evaluation of bio-physico-chemical, rheological, and gel-forming capabilities, as well as product yield, W2 may be the best option for producing high-quality surimi from Indian mackerel in a sustainable manner.

Protective Potential of Uric Acid, Folic Acid, Glutathione and Ascorbic Acid Against the Formation of Toxic Met-Myoglobin

BACKGROUND

Myoglobin is an oxygen binding protein and its dysfunction has been associated with the pathology of several human disorders. This study was undertaken to investigation the role of hydrogen peroxide (H2O2) in the formation of met-myoglobin and the protective potential of four different reductants such as uric acid, folic acid, glutathione and ascorbic acid were also tested against met-myoglobin formation.

METHODS

Human myoglobin was treated with H2O2 in-vitro in order to prepare met-myoglobin. The generation of met-myoglobin was confirmed by UV-visible spectroscopy and its stability was analysed by the treatment of human myoglobin with H2O2 at varying pH or time. High performance liquid chromatography (HPLC) was used to determine the oxidatively modified heme products in met-myoglobin. Spectroscopic analysis was used to identify the protective potential of uric acid, folic acid, glutathione and ascorbic acid against the formation of met-myoglobin.

RESULTS

The novel data of this study showed that H2O2 induced extensive damage of myoglobin but the treatment with uric acid, folic acid, glutathione or ascorbic acid provides protection of myoglobin against H2O2 induced oxidative damaged. The study apparently proved the protective potential of all these compounds against the toxicity produced by H2O2.

CONCLUSION

This is the first study that shows uric acid, folic acid, glutathione and ascorbic acid provide protection against the generation of toxic met-myoglobin and might be used therapeutically to modify the blood conditions in order to prevent the progression of human disorders associated with myoglobin dysfunction.

Effect of Polymer Hydrophilicity and Molar Mass on the Properties of the Protein in Protein-Polymer Conjugates: The Case of PPEylated Myoglobin

Polyphosphoesters (PPEs), a versatile class of biodegradable and biocompatible polymers, have been proposed as alternatives to poly(ethylene glycol) (PEG), which is suspected to be responsible for anaphylactic reactions in some patients after the administration of PEGylated compounds, e.g., in the current Covid-19 vaccines. We present the synthesis and characterization of a novel set of protein-polymer conjugates using the model protein myoglobin and a set of PPEs with different hydrophilicity and molar mass. We report an extensive evaluation of the (bio)physical properties of the protein within the conjugates, studying its conformation, residual activity, and thermal stability by complementary techniques (UV-vis spectroscopy, nano-differential scanning calorimetry, and fluorometry). The data underline the systematic influence of polymer hydrophilicity on protein properties. The more hydrophobic polymers destabilize the protein, the more hydrophilic PPEs protect against thermally induced aggregation and proteolytic degradation. This basic study aims at guiding the design of future PPEylated drugs and protein conjugates.

Design of oriented mesoporous silica films for guiding protein adsorption states

The highly-oriented cylindrical mesoporous silica films were synthesized on the rubbing-treated polyimide by adjusting the molar ratio of the orientation-directing agent (Brij56) to the structure-directing agent (P123) as surfactants in the silica precursor solutions for guiding protein adsorption states. As a result, the diameter and the orientation degree of mesopores changed with the molar ratio of Brij56 to P123. The maximum orientation degree (93%) of cylindrical mesopores oriented in the direction perpendicular to the rubbing direction was observed when the molar ratio of Brij56 to P123 was 3. Then, the dissolution features in simulated body fluid and the protein adsorption properties of the oriented cylindrical mesoporous silica films were investigated. The silica skeletons were gradually dissolved from the upper film surfaces and subsequently, the mesopore structures were collapsed when the films were immersed for 90 min. Moreover, the protein adsorption amount and the ratio from the mono-component and two-component solutions on the films were higher than those on the unoriented cylindrical mesoporous silica films due to the formation of open-ended cylindrical mesopore shapes and sizes. In addition, the shapes of the proteins adsorbed on the films had anisotropy, which would be reflected by the cylindrical mesopore shapes generated by the dissolution of silica layers and subsequent exposure of inner mesopore surfaces. Therefore, the synthesized highly-oriented cylindrical mesoporous silica films were useful to adsorb mesoscale biomolecules such as proteins and can effectively guide their anisotropic adsorption shapes, and therefore have the potential to be used as surface-coating films of polyimide in biomedical fields.

Biological Stimuli-Induced Phase Transition of a Synthesized Block Copolymer: Preferential Interactions between PNIPAM-b-PNVCL and Heme Proteins

The beguiling world of functional polymers is dominated by thermoresponsive polymers with unique structural and molecular attributes. Limited work has been reported on the protein-induced conformational transition of block copolymers; furthermore, the literature lacks a clear understanding of the influence of proteins on the phase behavior of thermoresponsive copolymers. Herein, we have synthesized poly(N-isopropylacrylamide)-b-poly(N-vinylcaprolactam) (PNIPAM-b-PNVCL) by RAFT polymerization using N-isopropylacrylamide and N-vinylcaprolactam. Furthermore, using various biophysical techniques, we have explored the effect of cytochrome c (Cyt c), myoglobin (Mb), and hemoglobin (Hb) with varying concentrations on the aggregation behavior of PNIPAM-b-PNVCL. Absorption and steady-state fluorescence spectroscopy measurements were performed at room temperature to examine the copolymerization effect on fluorescent probe binding and biomolecular interactions between PNIPAM-b-PNVCL and proteins. Furthermore, temperature-dependent fluorescence spectroscopy and dynamic light scattering studies were performed to get deeper insights into the lower critical solution temperature (LCST) of PNIPAM-b-PNVCL. Small-angle neutron scattering (SANS) was also employed to understand the copolymer behavior in the presence of heme proteins. With the incorporation of proteins to PNIPAM-b-PNVCL aqueous solution, LCST has been varied to different extents owing to the preferential, molecular, and noncovalent interactions between PNIPAM-b-PNVCL and proteins. The present study can pave new insights between heme proteins and block copolymer interactions, which will help design biomimetic surfaces and aid in the strategic fabrication of copolymer-protein bioconjugates.

Considerations on Protein Stability During Freezing and Its Impact on the Freeze-Drying Cycle: A Design Space Approach

Freezing is widely used during the manufacturing process of protein-based therapeutics, but it may result in undesired loss of biological activity. Many variables come into play during freezing that could adversely affect protein stability, creating a complex landscape of interrelated effects. The current approach to the selection of freezing conditions is however nonsystematic, resulting in poor process control. Here we show how mathematical models, and a design space approach, can guide the selection of the optimal freezing protocol, focusing on protein stability. Two opposite scenarios are identified, suggesting that the ice-water interface is the dominant cause of denaturation for proteins with high bulk stability, while the duration of the freezing process itself is the key parameter to be controlled for proteins that are susceptible to cold denaturation. Experimental data for lactate dehydrogenase and myoglobin as model proteins support the model results, with a slow freezing rate being optimal for lactate dehydrogenase and the opposite being true for myoglobin. A possible application of the calculated design space to the freezing and freeze-drying of biopharmaceuticals is finally described, and some considerations on process efficiency are discussed as well.

Transcriptomic Identification and Biochemical Characterization of HmpA, a Nitric Oxide Dioxygenase, Essential for Pathogenesis of Vibrio vulnificus

Nitric oxide (NO) and its derivatives are important effectors of host innate immunity, disrupting cellular function of infecting pathogens. Transcriptome analysis of Vibrio vulnificus, an opportunistic human pathogen, identified a set of genes induced upon exposure to NO. Among them, VvhmpA (V. vulnificus hmpA), encoding a multidomain NO dioxygenase, was the most greatly induced upon exposure to NO and was thus further characterized. Absorption spectra demonstrated that VvHmpA is a heme protein in which the heme iron can exist in either reduced, NO-bound, or oxidized state. Biochemical studies revealed that VvHmpA is a flavohemoglobin containing equimolar amounts of heme and FAD as cofactors. The K_M and k_cat values of VvHmpA for NO at 37°C, the temperature encountered by V. vulnificus in the host, were greater than those at 30°C, indicating that VvHmpA detoxifies high levels of NO effectively during infection. Compared with the wild type, the VvhmpA mutant exhibited a lower NO-decomposition activity and impaired growth in the presence of NO in vitro. Also, the cytotoxicity and survival of the VvhmpA mutant infecting the NO-producing murine macrophage cells were lower than those of the wild type. Furthermore, the mouse lethality of the VvhmpA mutant was reduced compared to that of the parental wild type. The combined results revealed that VvHmpA is a potent virulence factor that is induced upon exposure to NO and important for the survival and pathogenesis of V. vulnificus during infection.

Impacts of low concentration surfactant on red blood cell dielectrophoretic responses

Cell dielectrophoretic responses have been extensively studied for biomarker expression, blood typing, sepsis, circulating tumor cell separations, and others. Surfactants are often added to the analytical buffer in electrokinetic cellular microfluidic systems to lower surface/interfacial tensions. In nonelectrokinetic systems, surfactants influence cell size, shape, and agglomeration; this has not been systematically documented in electrokinetic systems. In the present work, the impacts of the Triton X-100 surfactant on human red blood cells (RBCs) were explored via ultraviolet-visible spectroscopy (UV-Vis) and dielectrophoresis (DEP) to compare nonelectrokinetic and electrokinetic responses, respectively. The UV-Vis spectra of Triton X-100 treated RBCs were dramatically different from that of native RBCs. DEP responses of RBCs were compared to RBCs treated with low concentrations of Triton X-100 (0.07-0.17 mM) to ascertain surfactant effects on dielectric properties. A star-shaped electrode design was used to quantify RBC dielectric properties by fitting a single-shell oblate cell model to experimentally-derived DEP spectra. The presence of 0.07 and 0.11 mM of Triton X-100 shifted the RBC's DEP spectra yielding lower crossover frequencies ( f C O ) . The single-shell oblate model revealed that cell radius and membrane permittivity are the dominant influencers of DEP spectral shifts. The trends observed were similar for 0.11 mM and 0.07 mM Triton X-100 treated cells. However, a further increase of Triton X-100 to 0.17 mM caused cells to only exhibit negative DEP. The magnitude of the DEP force increased with Triton X-100 concentration. This work indicates that dynamic surfactant interactions with cell membranes alter cell dielectric responses and properties.

Comprehensive Insight into the Protein-Surface Biomolecular Interactions on a Smart Material: Complex Formation between Poly(N-vinyl Caprolactam) and Heme Protein

Proteins are naturally occurring biopolymers that exhibit a wide range of functional applications. Meticulous knowledge about biomolecular interactions between polymeric biomaterials and body fluids or proteins is essential for designing biospecific surfaces and understanding protein-polymer interactions beyond existing limitations. In this regard, we studied the comparative effect of heme proteins such as cytochrome c, myoglobin, and hemoglobin on the phase behavior of poly(N-vinyl caprolactam) (PVCL) aqueous solution and demonstrated various biomolecular interactions in the polymer-protein complex with the aid of various biophysical techniques. Absorption spectroscopy, steady-state fluorescence spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering studies, laser Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy were carried out at room temperature to examine the changes in absorbance, fluorescence intensity, molecular interactions, particle size, agglomeration behavior, and surface morphologies. Furthermore, differential scanning calorimetry studies were also performed to analyze conformational changes, coil to globule transition, and phase behavior in the presence of proteins. With the addition of heme proteins, the lower critical solution temperature of PVCL increases toward higher temperature. The present study may help in designing smart biomaterials and stimulate more novel concepts in polymer-protein interactions. It also helps in the development of a biomimetic polymer for "smart" applications such as pulsatile drug release systems and controlled bioadhesion by temperature-mediated hydrophilic/hydrophobic switching.

Food additive dye (quinoline yellow) promotes unfolding and aggregation of myoglobin: A spectroscopic and molecular docking analysis

Protein aggregation leads to vast conformational changes and plays a key role in the pathogenesis of various neurodegenerative diseases including Alzheimer's and Parkinson's. In the current piece of work, we have explored the interaction of quinoline yellow (QY) with myoglobin (Mb) at two different pH (3.5 and 7.4). Various spectroscopic techniques such as turbidity, Rayleigh light scattering (RLS), UV-Vis absorbance, fluorescence resonance energy transfer (FRET), far UV-CD along with transmission electron microscopy (TEM) and molecular docking have been utilized to characterize dye-induced aggregation in Mb. Binding results showed that interaction between QY and myoglobin is spontaneous and static in nature with high K_SV value of 2.14 × 10⁴ M^-1. On the other hand, thermodynamics studies (∆H & ∆S) revealed that complex formation was driven by hydrogen and Van der Walls forces. Molecular docking analysis showed strong binding affinity (K_d = 4.95 × 10⁴ M^-1) between QY and Mb at Pro100, Ile101, Lys102, Glu105, Glu136, Arg139, Lys140, and Ala143 residues. The intrinsic fluorescence and circular dichroism studies indicated that QY induced conformational changes in Mb at pH 3.5. Turbidity and RLS studies showed aggregation of Mb in the presence of QY (0.2-5 mM). Moreover, kinetics data revealed nucleation independent aggregation of myoglobin in the presence of QY. TEM analysis further established amorphous nature of Mb aggregate induced by QY. At pH (7.4), QY was unable to induce aggregation in myoglobin; it might be due to repulsive nature of negatively charged dye and myoglobin or partially altered states of protein could be pre-requisite for binding and aggregation.

Effect of silicone on the collagen fibrillogenesis and stability

Collagen, the most abundant protein in mammals, is able to form fibrils, which have central role in tissue repair, fibrosis, and tumor invasion. As a component of skin, tendons, and cartilages, this protein contacts with any implanted materials. An inherent problem associated with implanted prostheses is their propensity to be coated with host proteins shortly after implantation. Also, silicone implants undergoing relatively long periods of contact with blood can lead to formation of thrombi and emboli. In this paper, we demonstrate the existence of interactions between siloxanes and collagen. Low-molecular-weight cyclic siloxane (hexamethylcyclotrisiloxane—D3) and polydimethylsiloxanes (PDMS) forming linear chains, ranging in viscosity from 20 to 12,000 cSt, were analyzed. We show that D3 as well as short-chain PDMS interact with collagen, resulting in a decrease in fibrillogenesis. However, loss of collagen native structure does not occur because of these interactions. Rather, collagen seems to be sequestered in its native form in an interlayer formed by collagen–siloxane complexes. On the other hand, silicone molecules with longer chains (i.e., PDMS with viscosity of 1000 and 12,000 cSt, the highest viscosity analyzed here) demonstrate little interaction with this protein and do not seem to affect collagen activity. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:1275–1281, 2015

Microcontact peeling as a new method for cell micropatterning

Micropatterning is becoming a powerful tool for studying morphogenetic and differentiation processes of cells. Here we describe a new micropatterning technique, which we refer to as microcontact peeling. Polydimethylsiloxane (PDMS) substrates were treated with oxygen plasma, and the resulting hydrophilic layer of the surface was locally peeled off through direct contact with a peeling stamp made of aluminum, copper, or silicon. A hydrophobic layer of PDMS could be selectively exposed only at the places of the physical contact as revealed by water contact angle measurements and angle-resolved X-ray photoelectron spectroscopy, which thus enabled successful micropatterning of cells with micro-featured peeling stamps. This new micropatterning technique needs no procedure for directly adsorbing proteins to bare PDMS in contrast to conventional techniques using a microcontact printing stamp. Given the several unique characteristics, the present technique based on the peel-off of inorganic materials may become a useful option for performing cell micropatterning.

Measuring interactions between polydimethylsiloxane and serum proteins at the air-water interface

The interaction between synthetic polymers and proteins at interfaces is relevant to basic science as well as a wide range of applications in biotechnology and medicine. One particularly common and important interface is the air-water interface (AWI). Due to the special energetics and dynamics of molecules at the AWI, the interplay between synthetic polymer and protein can be very different from that in bulk solution. In this paper, we applied the Langmuir-Blodgett technique and fluorescence microscopy to investigate how the compression state of polydimethylsiloxane (PDMS) film at the AWI affects the subsequent adsorption of serum protein [e.g., human serum albumin (HSA) or immunoglobulin G (IgG)] and the interaction between PDMS and protein. Of particular note is our observation of circular PDMS domains with micrometer diameters that form at the AWI in the highly compressed state of the surface film: proteins were shown to adsorb preferentially to the surface of these circular PDMS domains, accompanied by a greater than 4-fold increase in protein found in the interfacial film. The PDMS-only film and the PDMS-IgG composite film were transferred to cover glass, and platinum-carbon replicas of the transferred films were further characterized by scanning electron microscopy and atomic force microscopy. We conclude that the structure of the PDMS film greatly affects the amount and distribution of protein at the interface.

Visible and ultraviolet spectroscopy of gas phase protein ions

Optical spectroscopy has contributed enormously to our knowledge of the structure and dynamics of atoms and molecules and is now emerging as a cornerstone of the gas phase methods available for investigating biomolecular ions. This article focuses on the UV and visible spectroscopy of peptide and protein ions stored in ion traps, with emphasis placed on recent results obtained on protein polyanions, by electron photodetachment experiments. We show that among a large number of possible de-excitation pathways, the relaxation of biomolecular polyanions is mainly achieved by electron emission following photo-excitation in electronically excited states. Electron photodetachment is a fast process that occurs prior to relaxation on vibrational degrees of freedom. Electron photodetachment yield can then be used to record gas phase action spectra for systems as large as entire proteins, without the limitation of system size that would arise from energy redistribution on numerous modes and prevent fragmentation after the absorption of a photon. The optical activity of proteins in the near UV is directly related to the electronic structure and optical absorption of aromatic amino acids (Trp, Phe and Tyr). UV spectra for peptides and proteins containing neutral, deprotonated and radical aromatic amino acids were recorded. They displayed strong bathochromic shifts. In particular, the results outline the privileged role played by open shell ions in molecular spectroscopy which, in the case of biomolecules, is directly related to their reactivity and biological functions. The optical shifts observed are sufficient to provide unambiguous fingerprints of the electronic structure of chromophores without the requirement of theoretical calculations. They constitute benchmarks for calculating the absorption spectra of chromophores embedded in entire proteins and could be used in the future to study biochemical processes in the gas phase involving charge transfer in aromatic amino acids, such as in the mediation of electron transfer or redox reactions. We then addressed the important question of the sensitivity of protein optical spectra to the intrinsic properties of protein ions, including conformation, charge state, etc., and to environmental factors. We report optical spectra for different charge states of insulin, for ubiquitin starting from native and denaturated solutions, and for apo-myoglobin protein. All these spectra are compared critically to spectra recorded in solution, in order to assess solvent effects. We also report the spectra of peptides complexed with metal cations and show that complexation gives rise to new optical transitions related to charge transfer types of excitation. The perspectives of this work include integrative approaches where UV-Vis spectroscopy could, for example, be combined with ion mobility spectrometry and high level calculations for protein structural characterization. It could also be used in spectroscopy to probe biological processes in the gas phase, with different light sources including VUV radiation (to probe different types of excitations) and ultra short pulses with time and phase modulation (to probe and control the dynamics of de-excitation or charge transfer events), and with the derivatization of proteins with chromophores to modulate their optical properties. We also envision that photo-excitation will play an important role in the future to produce intermediates with new chemical and reactive properties. Another promising route is to conduct activated electron photodetachment dissociation experiments.

Femtosecond Coherence Spectroscopic Study of the Onset of Chemical Denaturation of Myoglobin upon Addition of Minor Amounts of Urea

The interaction of urea with myoglobin, as a benchmark system for heme-containing proteins, is studiedviafemtosecond coherence spectroscopy. The work focuses on the effect of urea on the appearance of low-wavenumber oscillations, which are a measure of the geometrical structure of the heme group and its interaction with the polypeptide chain. Pursuing this approach, structural alterations (i.e.changes in the vibrational dynamics of the heme group) are detected at denaturant concentrations below the full denaturation limit of 6 M urea for myoglobin. In particular, the low-wavenumber oscillation associated with the heme-doming (i.e.the out-off-plane vibration of the propyrin macrocycle) is found to appear spectrally shifted with a concentration of only 3 M urea. These results suggest that the local environment around the heme is already altered despite the fact that macroscopic unfolding as manifested in the thermodynamic properties of the polypeptide chain is not complete at these urea concentrations.

Characterization of hemoglobin immobilized in MgAl-layered double hydroxides by the coprecipitation method

Hemoglobin was immobilized in Mg(2)Al-Layered Double Hydroxides (LDH) by coprecipation method at pH 9.0. Interactions between Hb and LDH particles were investigated by X-ray diffraction patterns, FTIR, UV-vis, circular dichroism, and fluorescence spectroscopies. Morphology and porosity of Mg(2)Al-Hb(cop) biohybrid are analyzed from SEM and TEM images and permeability measurement. The direct electron transfer of immobilized Hb was studied by cyclic voltammetry, and the electrocatalytic activity was evaluated at glassy carbon modified with this Mg(2)Al-Hb(cop) biohybrid. Even though the percentage of electroactive Hb was less than 2%, this bioelectrode showed a low detection limit (1.5 x 10(-8) M) and a very high sensitivity (37 A/M cm(2)) for the amperometric detection of H(2)O(2).

Templated protein assembly on micro-contact-printed surface patterns. Use of the SNAP-tag protein functionality

Micro contact printing (microCP) has been established as a simple technique for high-resolution protein patterning for micro- and nanoarrays. However, as biochemical assays based on immobilized protein arrays progress from immunoassays to more delicate functional assays, the demand for methods of miniaturized, gentle, and oriented immobilization, which are applicable to many different target proteins, becomes larger. In this study, we present a novel microCP templated assembly approach, based on a recombinant SNAP-FLAG-HIS 10 (SFH) immobilization vehicle, which exploits the recently developed SNAP-tag protein. The SNAP-tag is derived from the human DNA repair protein hAGT, which covalently transfers the alkyl group of benzyl guanine (BG) substrates onto itself. We have designed a model SFH cassette carrying three tags (SNAP-tag, FLAG-tag, and HIS-tag), each of which can be used for fluorescence labeling or surface immobilization. When patterns of streptavidin modified with BG-biotin (streptavidin-BG) are stamped onto a surface, the SFH can subsequently assemble on the ligand pattern from solution, functioning as a general immobilization vehicle for high-resolution patterning of any protein expressed in the SFH cassette, in a gentle and oriented manner. Alternatively, the SFH can be site-selectively biotinylated using BG-biotin and, subsequently, assemble on stamped streptavidin. We exploit several ways to biotinylate the SFH protein via the SNAP-tag, promoting its templated assembly on micropatterns of streptavidin in four complementary formats. Quantitative analysis of the obtained patterns, revealed by immunostaining, indicates that all four approaches resulted in proper SFH immobilization and antibody recognition, demonstrating the versatility of the SFH cassette and the potential for high resolution patterning applications. Also, our data confirm that streptavidin can be stamped directly on surfaces, without loss of activity. While three strategies resulted in similar patterning efficiencies, one particular approach--namely templated assembly of SFH directly on streptavidin-BG patterns--resulted in an order of magnitude increase in patterning efficiency.

Delivery of both active enzyme and bleach from water-in-silicone oil (D(4)) emulsions

Advanced cleaning formulations, such as liquid laundry packages, consist of many components that require a complex mixture of interfacial actives including silicones for foam control, bleach for brightening, and enzymes for stain removal. Many of these ingredients are mutually incompatible, particularly in liquid formulations where they can be in intimate contact over extended periods of time. Solid dispersions of a prototypical bleach, NaBO3, in silicone polyether surfactants were shown to be very stable over time, even in the presence of water-in-silicone (D(4)) emulsions containing the enzyme alpha-chymotrypsin. Normally, perborates undergo rapid decomposition on contact with water. The rate of denaturation of the enzyme in the emulsion was similarly unaffected by the presence of the bleach until the emulsion was broken, unlike the case where the polyether surfactant was not present. The polyether surfactant thus protects the perborate from hydration and the enzyme from denaturing on contact with silicone oil until excess water and high shear are applied to the emulsion; protective mechanisms are discussed.

Microcontact printing: A tool to pattern

Microcontact printing has proven to be a useful technique in the patterned functionalization of certain chemicals onto surfaces. It has been particularly valuable in the patterning of biological materials. In this review, we describe the basic principles of the technology as well as its use in several applications, with an emphasis on biological ones. We also discuss the limitations and future directions of this method.

Structural and redox properties of mitochondrial cytochrome c co-sorbed with phosphate on hematite (α-Fe2O3) surfaces

The interaction of metalloproteins with oxides has implications not only for bioanalytical systems and biosensors but also in the areas of biomimetic photovoltaic devices, bioremediation, and bacterial metal reduction. Here, we investigate mitochondrial ferricytochrome c (Cyt c) co-sorption with 0.01 and 0.1 M phosphate on hematite (alpha-Fe2O3) surfaces as a function of pH (2-11). Although Cyt c sorption to hematite in the presence of phosphate is consistent with electrostatic attraction, other forces act upon Cyt c as well. The occurrence of multilayer adsorption, and our AFM observations, suggest that Cyt c aggregates as the pH approaches the Cyt c isoelectric point. In solution, methionine coordination of heme Fe occurs only between pH 3 and 7, but in the presence of phosphate this coordination is retained up to pH 10. Electrochemical evidence for the presence of native Cyt c occurs down to pH 3 and up to pH 10 in the absence of phosphate, and this range is extended to pH 2 and 11 in the presence of phosphate. Cyt c that initially adsorbs to a hematite surface may undergo conformation change and coat the surface with unfolded protein such that subsequently adsorbing protein is more likely to retain the native conformational state. AFM provides evidence for rapid sorption kinetics for Cyt c co-sorbed with 0.01 or 0.1 M phosphate. Cyt c co-sorbed with 0.01 M phosphate appears to unfold on the surface of hematite while Cyt c co-sorbed with 0.1 M phosphate possibly retains native conformation due to aggregation.

In vitro measurement of conformational stability of fibrinogen adsorbed on siloxane

The paper describes the effect of 10-, 50-, 100-, 200-, 300-, 400-, and 500-fold excess of low-molecular weight, linear, hexamethyldisiloxane (L(2)) and cyclic hexamethylcyclotrisiloxane (D(3)) with respect to fibrinogen (Fbg) on the conformational stability of Fbg during a 60-h incubation at 37 degrees C. This study used SPE/HPLC/UV and fluorescence of a tryptophan located in the domain of Fbg and fluorescence of 1,1'-bis(4-anilino)naphthalene-5,5'-disulfonic acid (ANS) spectroscopy. The fact that the decrease in fluorescence intensity of siloxane-treated Fbg was accompanied by red shift in the maximum wavelength indicated that denaturation of Fbg had taken place. The differences (the decrease in peak height and the shift in retention time) in chromatograms between control Fbg and siloxane-treated Fbg indicated the adsorption process of Fbg on the surface of siloxanes. Incubating hexamethyldisiloxane with Fbg at L(2)-to-Fbg ratios >300 for 20 h yielded white and mould-like precipitates of Fbg. The same phenomenon demonstrating massive denaturation and aggregation was observed for a greater than 500-fold excess of D(3) with respect to Fbg after 20 h of incubation.

The measurement of conformational stability of proteins adsorbed on siloxanes

The paper investigates the conformational stability of bovine serum albumin (BSA) and fibrinogen during 24-h incubation in turn with a linear silicone polymer (polydimethylsiloxane (PDMS)), with linear silicone oligomers (hexamethyldisiloxane and octamethyltrisiloxane) and with cyclic silicone oligomers (octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5)). Ten-fold and 100-fold excesses of siloxanes with respect to the proteins were used. Using fluorescence spectroscopy of tryptophan located in the domain of proteins and fluorescence of 8-anilino-1-naphthalenesulfonic acid (1,8-ANS), which interacts with hydrophobic domains of proteins, changes in the tertiary structure of the protein were recorded. The results demonstrated that BSA does not change its native form during 24-h incubation with siloxanes. In contrast, the tertiary structure of fibrinogen was found to be altered by both short-chain linear siloxanes: (hexamethyldisiloxane and octamethyltrisiloxane) and long-chain PDMS. The changes can be observed only at a 100-fold excess of siloxanes with respect to the protein. No conformational changes in fibrinogen exposed to cyclic siloxanes were observed.

Tryptophan phosphorescence as a monitor of protein conformation in molecular films

This report enquires on the potentiality of Trp phosphorescence for probing the conformational state of proteins deposited on solid dry films. Thin, amorphous protein films were fabricated with Apoazurin, alcohol dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase and glutamate dehydrogenase the protein being incorporated into a DEAE-dextran matrix and deposited on quartz slides. The results, obtained with appositely constructed instrumentation, demonstrate that thanks to the low background radiation associated with long-lived, delayed emission phosphorescence can be readily detected down to single protein layer matrices and that both spectrum and lifetime are important indicators of the integrity of the protein globular fold. In fact, denaturation of the proteins by guanidinium hydrochloride or heat treatment points out that disruption of the native fold leads to a red shift and broadening of the spectrum with loss of vibronic structure, accompanied to considerably shorter-lived and more heterogeneous decay kinetics. It is also shown that the sensitivity of the phosphorescence lifetime towards the detection of altered, looser conformations of the polypeptide are remarkably enhanced on partial hydration of the sample.

Structural perturbations of azurin deposited on solid matrices as revealed by trp phosphorescence

The phosphorescence emission of Cd-azurin from Pseudomonas aeruginosa was used as a probe of possible perturbations in the dynamical structure of the protein core that may be induced by protein-sorbent and protein-protein interactions occurring when the macromolecule is deposited into amorphous, thin solid films. Relative to the protein in aqueous solution, the spectrum is unrelaxed and the phosphorescence decay becomes highly heterogeneous, the average lifetime increasing sharply with film thickness and upon its dehydration. According to the lifetime parameter, adsorption of the protein to the substrate is found to produce a multiplicity of partially unfolded structures, an influence that propagates for several protein layers from the surface. Among the substrates used for film deposition, hydrophilic silica, dextran, DEAE-dextran, dextran sulfate, and hydrophobic octodecylamine, the perturbation is smallest with dextran sulfate and largest with octodecylamine. The destabilizing effect of protein-protein interactions, as monitored on 50-layer-thick films, is most evident at a relative humidity of 75%. Stabilizing agents were incorporated to attenuate the deleterious effects of protein aggregation. Among them, the most effective in preserving a more native-like structure are the disaccharides sucrose and trehalose in dry films and the polymer dextran in wet films. Interestingly, the polymer was found to achieve maximum efficacy at sensibly lower additive/protein ratios than the sugars.