High probability of disrupting a disulphide bridge mediated by an endogenous excited tryptophan residue

Carotenoid-dependent singlet oxygen photogeneration in light-harvesting complex 2 of Ectothiorhodospira haloalkaliphila leads to the formation of organic hydroperoxides and damage to both pigments and protein matrix

Earlier, it was suggested that carotenoids in light-harvesting complexes 2 (LH2) can generate singlet oxygen, further oxidizing bacteriochlorophyll to 3-acetyl-chlorophyll. In the present work, it was found that illumination of isolated LH2 preparations of purple sulfur bacterium Ectothiorhodospira haloalkaliphila with light in the carotenoid absorption region leads to the photoconsumption of molecular oxygen, which is accompanied by the formation of hydroperoxides of organic molecules in the complexes. Photoformation of two types of organic hydroperoxides were revealed: highly lipophilic (12 molecules per one LH2) and relatively hydrophobic (68 per one LH2). It has been shown that illumination leads to damage to light-harvesting complexes. On the one hand, photobleaching of bacteriochlorophyll and a decrease in its fluorescence intensity are observed. On the other hand, the photoinduced increase in the hydrodynamic radius of the complexes, the reduction in their thermal stability, and the change in fluorescence intensity indicate conformational changes occurring in the protein molecules of the LH2 preparations. Inhibition of the processes described above upon the addition of singlet oxygen quenchers (L-histidine, Trolox, sodium L-ascorbate) may support the hypothesis that carotenoids in LH2 preparations are capable of generating singlet oxygen, which, in turn, damage to protein molecules.

Protein-modified nanomaterials: emerging trends in skin wound healing

Prolonged inflammation can impede wound healing, which is regulated by several proteins and cytokines, including IL-4, IL-10, IL-13, and TGF-β. Concentration-dependent effects of these molecules at the target site have been investigated by researchers to develop them as wound-healing agents by regulating signaling strength. Nanotechnology has provided a promising approach to achieve tissue-targeted delivery and increased effective concentration by developing protein-functionalized nanoparticles with growth factors (EGF, IGF, FGF, PDGF, TGF-β, TNF-α, and VEGF), antidiabetic wound-healing agents (insulin), and extracellular proteins (keratin, heparin, and silk fibroin). These molecules play critical roles in promoting cell proliferation, migration, ECM production, angiogenesis, and inflammation regulation. Therefore, protein-functionalized nanoparticles have emerged as a potential strategy for improving wound healing in delayed or impaired healing cases. This review summarizes the preparation and applications of these nanoparticles for normal or diabetic wound healing and highlights their potential to enhance wound healing.

Modification and oxidative degradation of β-lactoglobulin by UVB irradiation

Ultraviolet (UV) B irradiation induces protein modification, especially the conformational rearrangement of proteins, and is therefore promising as a non-thermal and non-chemical functionalization technique. Nevertheless, UVB irradiation introduces radicals and oxidizes side chains resulting in the loss of food quality. Thus, assessing the UVB irradiation-based functionalization of β-lactoglobulin (BLG) versus its oxidative degradation is of interest. UVB irradiation of up to 8 h was successfully applied to loosen the rigid folding of BLG and increase its flexibility. Thereby, the cysteine at position 121 and hydrophobic regions became surface-exposed as indicated by the increase in accessible thiol groups and increased surface hydrophobicity. Furthermore, we demonstrated the cleavage of the "outer" disulfide bond C⁶⁶-C¹⁶⁰ by LC-MS/MS after tryptic digestion of BLG. The 2-h-irradiated BLG showed adequate conformational rearrangement for protein functionalization while being minimally oxidized.

Role of charged residues of the "electrostatic loop" of hSOD1 in promotion of aggregation: Implications for the mechanism of ALS-associated mutations under amyloidogenic conditions

Protein misfolding and amyloid formation are hallmarks of numerous diseases, including amyotrophic lateral sclerosis (ALS), in which hSOD1 aggregation is involved in pathogenesis. We used two point mutations in the electrostatic loop, G138E and T137R, to analyze charge distribution under destabilizing circumstances to gain more about how ALS-linked mutations affect SOD1 protein stability or net repulsive charge. We show that protein charge is important in the ALS disease process using bioinformatics and experiments. The MD simulation findings demonstrate that the mutant protein differs significantly from WT SOD1, which is consistent with the experimental evidence. The specific activity of the wild type was 1.61 and 1.48 times higher than that of the G138E and T137R mutants, respectively. Under amyloid induction conditions, the intensity of intrinsic and ANS fluorescence in both mutants reduced. Increasing the content of β-sheet structures in mutants can be attributed to aggregation propensity, which was confirmed using CD polarimetry and FTIR spectroscopy. Our findings show that two ALS-related mutations promote the formation of amyloid-like aggregates at near physiological pH under destabilizing conditions, which were detected using spectroscopic probes such as Congo red and ThT fluorescence, and also further confirmation of amyloid-like species by TEM. Overall, our results provide evidence supporting the notion that negative charge changes combined with other destabilizing factors play an important role in increasing protein aggregation by reducing repulsive negative charges.

Photoinduced chlorophyll charge transfer state identified in the light-harvesting complex II from a marine green alga Bryopsis corticulans

The light-harvesting complex II of Bryopsis corticulans (B-LHCII), a green alga, differs from that of spinach (S-LHCII) in chlorophyll (Chl) and carotenoid (Car) compositions. We investigated ultrafast excitation dynamics of B-LHCII with visible-to-near infrared time-resolved absorption spectroscopy. Absolute fluorescence quantum yield (Φ _FL) of LHCII and spectroelectrochemical (SEC) spectra of Chl a and b were measured to assist the spectral analysis. Red-light excitation at Chl Q_y-band, but not Car-band, induced transient features resembling the characteristic SEC spectra of Chl a ^⋅+ and Chl b ^⋅-, indicating ultrafast photogeneration of Chl-Chl charge transfer (CT) species; Φ _FL and ³Car^∗ declined whereas CT species increased upon prolonging excitation wavelength, showing positive correlation of ¹Chl^∗ deactivation with Chl-Chl CT formation. Moreover, ultrafast Chl b-to-Chl a and Car-to-Chl singlet excitation transfer were illustrated. The red-light induction of Chl-Chl CT species, as also observed for S-LHCII, is considered a general occurrence for LHCIIs in light-harvesting form.

Transdermal delivery of a somatostatin receptor type 2 antagonist using microneedle patch technology for hypoglycemia prevention

Hypoglycemia is a serious and potentially fatal complication experienced by people with insulin-dependent diabetes. The complication is usually caused by insulin overdose, skipping meals, and/or excessive physical activities. In type 1 diabetes (T1D), on top of impaired pancreatic α-cells, excessive levels of somatostatin from δ-cells further inhibit glucagon secretion to counteract overdosed insulin. Herein, we aimed to develop a microneedle (MN) patch for transdermal delivery of a peptide (PRL-2903) that antagonizes somatostatin receptor type 2 (SSTR2) in α-cells. First, we investigated the efficacy of subcutaneously administered PRL-2903 and identified the optimal dose (i.e., the minimum effective dose) and treatment scheduling (i.e., the best administration time for hypoglycemia prevention) in a T1D rat model. We then designed an MN patch using a hyaluronic acid (HA)-based polymer. The possible effect of the polymer on stabilizing the native structure of PRL-2903 was studied by molecular dynamics (MD) simulations. The results showed that the HA-based polymer could stabilize the PRL-2903 structure by restricting water molecules, promoting intra-molecular H-bonding, and constraining torsional angles of important bonds. In vivo studies with an overdose insulin challenge revealed that the PRL-2903-loaded MN patch effectively increased the plasma glucagon level, restored the counter-regulation of blood glucose concentration, and prevented hypoglycemia. The proposed MN patch is the first demonstration of a transdermal microneedle patch designed to deliver an SSTR2 antagonist for the prevention of hypoglycemia. This counter-regulatory peptide delivery system may be applied alongside with insulin delivery systems to provide a more effective and safer treatment for people with insulin-dependent diabetes.

Ultrasensitive antibody-aptamer plasmonic biosensor for malaria biomarker detection in whole blood

Development of plasmonic biosensors combining reliability and ease of use is still a challenge. Gold nanoparticle arrays made by block copolymer micelle nanolithography (BCMN) stand out for their scalability, cost-effectiveness and tunable plasmonic properties, making them ideal substrates for fluorescence enhancement. Here, we describe a plasmon-enhanced fluorescence immunosensor for the specific and ultrasensitive detection of Plasmodium falciparum lactate dehydrogenase (PfLDH)—a malaria marker—in whole blood. Analyte recognition is realized by oriented antibodies immobilized in a close-packed configuration via the photochemical immobilization technique (PIT), with a top bioreceptor of nucleic acid aptamers recognizing a different surface of PfLDH in a sandwich conformation. The combination of BCMN and PIT enabled maximum control over the nanoparticle size and lattice constant as well as the distance of the fluorophore from the sensing surface. The device achieved a limit of detection smaller than 1 pg/mL (<30 fM) with very high specificity without any sample pretreatment. This limit of detection is several orders of magnitude lower than that found in malaria rapid diagnostic tests or even commercial ELISA kits. Thanks to its overall dimensions, ease of use and high-throughput analysis, the device can be used as a substrate in automated multi-well plate readers and improve the efficiency of conventional fluorescence immunoassays.

Reliable plasmonic biosensors with high throughput and ease of use are highly sought after. Here, the authors report a plasmon-enhanced fluorescence antibody-aptamer biosensor based on a gold nanoparticle array, and demonstrate its use for effective specific detection of a malaria marker, at femtomolar level, in whole blood.

Direct Ultraviolet Laser-Induced Reduction of Disulfide Bonds in Insulin and Vasopressin

Ultraviolet (UV) light has been shown to induce reduction of disulfide bonds in proteins in solution. The photoreduction is proposed to be a result of electron donation from excited Tyr or Trp residues. In this work, a powerful UV femtosecond laser was used to generate photoreduced products, while the hypothesis of Tyr/Trp mediation was studied with spectroscopy and mass spectrometry. With limited irradiation times of 3 min or less at 280 nm, the laser-induced reduction in arginine vasopressin and human insulin led to significant yields of ∼3% stable reduced product. The photogenerated thiols required acidic pH for stabilization, while neutral pH primarily caused scrambling and trisulfide formation. Interestingly, there was no direct evidence that Tyr/Trp mediation was a required criterion for the photoreduction of disulfide bonds. Intermolecular electron transfer remained a possibility for insulin but was ruled out for vasopressin. We propose that an additional mechanism should be increasingly considered in UV light-induced reduction of disulfide bonds in solution, in which a single UV photon is directly absorbed by the disulfide bond.

Biosensor surface functionalization by a simple photochemical immobilization of antibodies: experimental characterization by mass spectrometry and surface enhanced Raman spectroscopy

Surface functionalization is a key step in biosensing since it is the basis of an effective analyte recognition. Among all the bioreceptors, antibodies (Abs) play a key role thanks to their superior specificity, although the available immobilization strategies suffer from several drawbacks. When gold is the interacting surface, the recently introduced Photochemical Immobilization Technique (PIT) has been shown to be a quick, easy-to-use and very effective method to tether Abs oriented upright by means of thiols produced via tryptophan mediated disulphide bridge reduction. Although the molecular mechanism of this process is quite well identified, the detailed morphology of the immobilized antibodies is still elusive due to inherent difficulties related to the microscopy imaging of Abs. The combination of Mass Spectrometry, Surface-Enhanced Raman Spectroscopy and Ellman's assay demonstrates that Abs irradiated under the conditions in which PIT is realized show only two effective disulphide bridges available for binding. They are located in the constant region of the immunoglobulin light chain so that the most likely position Ab assumes is side-on, i.e. with one Fab (i.e. the antigen binding portion of the antibody) exposed to the solution. This is not a limitation of the recognition efficiency in view of the intrinsic flexibility of the Ab structure, which makes the free Fab able to sway in the solution, a feature of great importance in many biosensing applications.

Excitation dynamics and relaxation in the major antenna of a marine green alga Bryopsis corticulans

The light-harvesting complexes II (LHCIIs) of spinach and Bryopsis corticulans as a green alga are similar in structure, but differ in carotenoid (Car) and chlorophyll (Chl) compositions. Carbonyl Cars siphonein (Spn) and siphonaxanthin (Spx) bind to B. corticulans LHCII likely in the sites as a pair of lutein (Lut) molecules bind to spinach LHCII in the central domain. To understand the light-harvesting and photoprotective properties of the algal LHCII, we compared its excitation dynamics and relaxation to those of spinach LHCII been well documented. It was found that B. corticulans LHCII exhibited a substantially longer chlorophyll (Chl) fluorescence lifetime (4.9 ns vs 4.1 ns) and a 60% increase of the fluorescence quantum yield. Photoexcitation populated ³Car* equally between Spn and Spx in B. corticulans LHCII, whereas predominantly at Lut620 in spinach LHCII. These results prove the functional differences of the LHCIIs with different Car pairs and Chl a/b ratios: B. corticulans LHCII shows the enhanced blue-green light absorption, the alleviated quenching of ¹Chl*, and the dual sites of quenching ³Chl*, which may facilitate its light-harvesting and photoprotection functions. Moreover, for both types of LHCIIs, the triplet excitation profiles revealed the involvement of extra ³Car* formation mechanisms besides the conventional Chl-to-Car triplet transfer, which are discussed in relation to the ultrafast processes of ¹Chl* quenching. Our experimental findings will be helpful in deepening the understanding of the light harvesting and photoprotection functions of B. corticulans living in the intertidal zone with dramatically changing light condition.

Screen Printed Based Impedimetric Immunosensor for Rapid Detection of Escherichia coli in Drinking Water

The development of a simple and low cost electrochemical impedance immunosensor based on screen printed gold electrode for rapid detection of Escherichia coli in water is reported. The immunosensor is fabricated by immobilizing anti-E. coli antibodies onto a gold surface in a covalent way by the photochemical immobilization technique, a simple procedure able to bind antibodies upright onto gold surfaces. Impedance spectra are recorded in 0.01 M phosphate buffer solution (PBS) containing 10 mM Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ as redox probe. The Nyquist plots can be modelled with a modified Randles circuit, identifying the charge transfer resistance R_ct as the relevant parameter after the immobilization of antibodies, the blocking with BSA and the binding of E. coli. The introduction of a standard amplification procedure leads to a significant enhancement of the impedance increase, which allows one to measure E. coli in drinking water with a limit of detection of 3 × 10¹ CFU mL⁻¹ while preserving the rapidity of the method that requires only 1 h to provide a “yes/no” response. Additionally, by applying the Langmuir adsorption model, we are able to describe the change of R_ct in terms of the “effective” electrode, which is modified by the detection of the analyte whose microscopic conducting properties can be quantified.

Characterization of Ultraviolet Photoreactions in Therapeutic Peptides by Femtosecond Laser Catalysis and Mass Spectrometry

Peptides and proteins have diverse ultraviolet (UV) photoreaction pathways that can be activated by the energy of the UV photons absorbed. Simple light sources such as lamps are conventionally used to study these photoreactions in solution. This work provides a proof of concept that femtosecond laser technology can function as a highly potent UV source in rapidly conducting UV photostability studies of peptides. Correspondingly, sufficient quantities of photoproducts were generated in 1 min or less, allowing for identification of known and new photomodifications in the therapeutic peptides somatostatin-14 and arginine vasopressin. Identical photoproducts were also generated with a conventional continuous source. The major modifications included N-formylkynurenine, a cross-link between Trp and Phe, a Tyr product with an NH₃ loss, and disruption of an unstable disulfide bond into a complex mixture of a trisulfide bond and multiple scrambled dimeric products. In conclusion, femtosecond lasers are extremely useful to drive fast UV-induced reactions for high throughput screening of photostability and modifications in amino acid polymers.

Tracing the 267 nm-Induced Radical Formation in Dimethyl Disulfide Using Time-Resolved X-ray Absorption Spectroscopy

Disulfide bonds are pivotal for the structure, function, and stability of proteins, and understanding ultraviolet (UV)-induced S-S bond cleavage is highly relevant for elucidating the fundamental mechanisms underlying protein photochemistry. Here, the near-UV photodecomposition mechanisms in gas-phase dimethyl disulfide, a prototype system with a S-S bond, are probed by ultrafast transient X-ray absorption spectroscopy. The evolving electronic structure during and after the dissociation is simultaneously monitored at the sulfur L_1,2,3-edges and the carbon K-edge with 100 fs (FWHM) temporal resolution using the broadband soft X-ray spectrum from a femtosecond high-order harmonics light source. Dissociation products are identified with the help of ADC and RASPT2 electronic-structure calculations. Rapid dissociation into two CH₃S radicals within 120 ± 30 fs is identified as the major relaxation pathway after excitation with 267 nm radiation. Additionally, a 30 ± 10% contribution from asymmetric CH₃S₂ + CH₃ dissociation is indicated by the appearance of CH₃ radicals, which is, however, at least partly the result of multiphoton excitation.

Biosensor for Point-of-Care Analysis of Immunoglobulins in Urine by Metal Enhanced Fluorescence from Gold Nanoparticles

Biosensors are easy-to-use and cost-effective devices that are emerging as an attractive tool, not only in settling diagnosis or in disease monitoring, but also in mass screening tests, a timely topic that impacts on daily life of the whole society. Nanotechnologies lend themselves to the development of highly sensitive devices whose realization has become a very interdisciplinary topic. Relying on the enhancement of the fluorescence signal detected at the surface of patterned gold nanoparticles, we report the behavior of an analytical device in detecting immunoglobulins in real urine samples that shows a limit of detection of approximately 8 μg/L and a linear range of 10-100 μg/L well below the detection limit of nephelometric method, which is the reference method for this analysis. These performances have been reached thanks to an effective surface functionalization technique and can be improved even more if superydrophobic features of the substrate we produce will be exploited. Since the analyte recognition is realized by antibodies the specificity is very high and, in fact, no interference has been detected by other compounds also present in the real urine samples. The device has been assessed on serum samples by comparing IgG concentrations values obtained by the biosensor with those provided by a nephelometer. In this step we found that our approach allows the analysis of the whole blood without any pretreatment; moreover, it is inherently extendable to the analysis of most biochemical markers in biological fluids.

Detection of miRNA cancer biomarkers using light activated Molecular Beacons

Early detection of cancer biomarkers can reduce cancer mortality rate. miRNAs are small non-coding RNAs whose expression changes upon the onset of various types of cancer. Biosensors that specifically detect such biomarkers can be engineered and integrated into point-of-care devices (POC) using label-free detection, high sensibility and compactness. In this paper, a new engineered Molecular Beacon (MB) construct used to detect miRNAs is presented. Such a construct is immobilized onto biosensor surfaces in a covalent and spatially oriented way using the photonic technology Light Assisted Molecular Immobilization (LAMI). The construct consists of a Cy3 labelled MB covalently attached to a light-switchable peptide. One MB construct contains a poly-A sequence in its loop region while the other contains a sequence complementary to the cancer biomarker miRNA-21. The constructs have been characterized by UV-Vis spectroscopy, mass spectrometry and HPLC. LAMI led to the successful immobilization of the engineered constructs onto thiol functionalized optically flat quartz slides and Silicon on Insulator (SOI) sensor surfaces. The immobilized Cy3 labelled MB construct has been imaged using confocal fluorescence microscopy (CFM). The bioavailability of the immobilized engineered MB biosensors was confirmed through specific hybridization with the Cy5 labelled complementary sequence and imaged by CFM and FRET. Hybridization kinetics have been monitored using steady state fluorescence spectroscopy. The label-free detection of miRNA-21 was also achieved by using integrated photonic sensing structures. The engineered light sensitive constructs can be immobilized onto thiol reactive surfaces and are currently being integrated in a POC device for the detection of cancer biomarkers.

Photonic based detection strategies of cancer miRNA biomarkers after Light Assisted Molecular Immobilization (LAMI) of peptide-MB biosensor constructs.

QCM-based immunosensor for rapid detection of Salmonella Typhimurium in food

Salmonella Typhimurium is one of the main causes of outbreaks and sporadic cases of human gastroenteritis. At present, the rapid detection of this pathogen is a major goal of biosensing technology applied to food safety. In fact, ISO standardized culture method takes up to ten days to provide a reliable response. In this paper, we describe a relatively simple protocol for detecting Salmonella Typhimurium in chicken meat based on a Quartz-Crystal Microbalance (QCM), which leads to a limit of detection (LOD) less than of 10° CFU/mL and requires a pre-enrichment step lasting only 2 h at 37 °C. The reliability of the proposed immunosensor has been demonstrated through the validation of the experimental results with ISO standardized culture method. The cost-effectiveness of the procedure and the rapidity of the QCM-based biosensor in providing the qualitative response make the analytical method described here suitable for applications in food inspection laboratory and throughout the chain production of food industry.

Microwave-radiation-induced molecular structural rearrangement of hen egg-white lysozyme

We have investigated the nonthermal effect of 10 GHz/22 dBm microwave radiation on hen egg-white lysozyme (HEWL) over different irradiation times, ranging from 2 min to 1 h. To ensure a control over the radiation parameters, a pair of microwave rectangular waveguides is used to irradiate the samples. Optical spectroscopic measurements, which include UV-visible absorption spectroscopy, Raman spectroscopy, and far UV CD spectroscopy, reveal the exposure of the buried tryptophan (Trp) residues of the native molecule between 15 and 30 min of radiation. The higher duration of the perturbation leads to a compact structure of the protein and Trp residues are buried again. Interestingly, we do not find any change in the secondary structure of the protein even for 1 h duration of radiation. The relaxation dynamics of the irradiated molecules also has been discussed. We have shown that the molecules relax to their native configuration in 7-8 h after the radiation field is turned off. The structural rearrangement over the above timescale has further been probed by a model calculation, based on a modified Langevin equation. Our coarse-grained simulation approach utilizes the mean of atomic positions and net atomic charge of each amino acid of native HEWL to mimic the initial conformation of the molecule. The modified positions of the residues are then calculated for the given force fields. The simulation results reveal the nonmonotonous change in overall size of the molecule, as observed experimentally. The radiation parameters used in our experiments are very similar to those of some of the electronic devices we often come across. Thus, we believe that the results of our studies on a simple protein structure may help us in understanding the effect of radiation on complex biological systems as well.

Nanoparticles provide long-term stability of bevacizumab preserving its antiangiogenic activity

Bevacizumab is one of the most common monoclonal antibodies used to treat cancer due to its antiangiogenic role. However, the frequent parenteral administrations are not attractive for the patient adhesion to the therapy. Nanoencapsulation of bevacizumab might be a useful alternative to increase administration intervals, due to controlled release properties. To achieve a long-term bevacizumab stability into PLGA nanoparticles, we developed an optimized and validated lyophilization protocol. The co-encapsulation of trehalose and bevacizumab into PLGA nanoparticles, associated to their lyophilization with external 10% (w/v) of trehalose, allowed maintenance of the physical-chemical characteristics of nanoparticles and bevacizumab secondary and tertiary structure. More relevant, the antiangiogenic activity of bevacizumab was kept over 6 months of storage while formulated with this protocol. No significant differences were found upon 6 months of storage at 4 °C and 25 °C/60% HR, and minor differences were observed for storage at 40 °C/75% HR, bringing to our knowledge, the first successfully report for monoclonal antibody storage at room temperature, without losing its structural and functional features. Our results served as starting point to understand the monoclonal antibody-based nanoparticle behavior over time, creating an innovative approach for a long-term monoclonal antibody stability.

STATEMENT OF SIGNIFICANCE

Nanoencapsulation of monoclonal antibodies has boost the interest of researchers as an alternative to the current antibody-based therapy, changing the route of administrations through controlled release of monoclonal antibodies. Despite good results have been achieved with nanoencapsulation process, no strategy has still found concerning a long-term stability of nanoparticles and monoclonal antibodies. In this study, the aim was to find out a validated and optimized method that allows a long-term stability of nanoparticles and antibodies. Over 6 months of storage, an optimized nanosystem was considered stable for both nanoparticles and antibody structure, at 4 °C and 25 °C, resulting the first successfully report for monoclonal antibody storage at room temperature.

Photochemical and Structural Studies on Cyclic Peptide Models

Ultra-violet (UV) irradiation has a significant impact on the structure and function of proteins that is supposed to be in relationship with the tryptophan-mediated photolysis of disulfide bonds. To investigate the correlation between the photoexcitation of Trp residues in polypeptides and the associated reduction of disulfide bridges, a series of small, cyclic oligopeptide models were analyzed in this work. Average distances between the aromatic side chains and the disulfide bridge were determined following molecular mechanics (MM) geometry optimizations. In this way, the possibility of cation–π interactions was also investigated. Molecular mechanics calculations revealed that the shortest distance between the side chain of the Trp residues and the disulfide bridge is approximately 5 Å in the cyclic pentapeptide models. Based on this, three tryptophan-containing cyclopeptide models were synthesized and analyzed by nuclear magnetic resonance (NMR) spectroscopy. Experimental data and detailed molecular dynamics (MD) simulations were in good agreement with MM geometry calculations. Selected model peptides were subjected to photolytic degradation to study the correlation of structural features and the photolytic cleavage of disulfide bonds in solution. Formation of free sulfhydryl groups upon illumination with near UV light was monitored by fluorescence spectroscopy after chemical derivatization with 7-diethylamino-3-(4-maleimidophenyl)-4-methylcoumarin (CPM) and mass spectrometry. Liquid cromatography-mass spectrometry (LC-MS) measurements indicated the presence of multiple photooxidation products (e.g., dimers, multimers and other oxidated products), suggesting that besides the photolysis of disulfide bonds secondary photolytic processes take place.

Copper-Mediated Polymerization without External Deoxygenation or Oxygen Scavengers

As a method for overcoming the challenge of rigorous deoxygenation in copper-mediated controlled radical polymerization processes [e.g., atom-transfer radical polymerization (ATRP)], reported here is a simple Cu0 -RDRP (RDRP=reversible deactivation radical polymerization) system in the absence of external additives (e.g., reducing agents, enzymes etc.). By simply adjusting the headspace of the reaction vessel, a wide range of monomers, namely acrylates, methacrylates, acrylamides, and styrene, can be polymerized in a controlled manner to yield polymers with low dispersities, near-quantitative conversions, and high end-group fidelity. Significantly, this approach is scalable (ca. 125 g), tolerant to elevated temperatures, compatible with both organic and aqueous media, and does not rely on external stimuli which may limit the monomer pool. The robustness and versatility of this methodology is further demonstrated by the applicability to other copper-mediated techniques, including conventional ATRP and light-mediated approaches.

Ultra-fast polymer optical fibre Bragg grating inscription for medical devices

We report the extraordinary result of rapid fibre Bragg grating inscription in doped polymer optical fibres based on polymethyl methacrylate in only 7 ms, which is two orders of magnitude faster than the inscription times previously reported. This was achieved using a new dopant material, diphenyl disulphide, which was found to enable a fast, positive refractive index change using a low ultraviolet dose. These changes were investigated and found to arise from photodissociation of the diphenyl disulphide molecule and subsequent molecular reorganization. We demonstrate that gratings inscribed in these fibres can exhibit at least a 15 times higher sensitivity than silica glass fibre, despite their quick inscription times. As a demonstration of the sensitivity, we selected a highly stringent situation, namely, the monitoring of a human heartbeat and respiratory functions. These findings could permit the inscription of fibre Bragg gratings during the fibre drawing process for mass production, allowing cost-effective, single-use, in vivo sensors among other potential uses.

Optically Assisted Surface Functionalization for Protein Arraying in Aqueous Media

Protein surface patterning is employed in a broad spectrum of applications ranging from protein microarray analysis to 2D cell organization. However, limitations arise because of the highly sensitive nature of proteins requiring careful handling to ensure their structural and functional integrity during the grafting process. Here, we describe a patterning protocol that keeps proteins in an aqueous environment during their immobilization, avoiding the loss of their biological activity. The procedure is based on the UV-mediated removal of polyethylene glycol self-assembled monolayers in a transparent microfluidic chamber, giving access to micrometric motifs of predefined geometries. Afterward, modified proteins can be grafted on the photopatterned domains. We also studied the influence of reactive oxygen species for a better understanding of the chemical mechanism involved in this process. Finally, as a proof of concept, a protein microarray was created with this process using cell-capturing antibodies to immobilize human blood cells, confirming the functionality of the arrayed proteins.

Effective antibodies immobilization and functionalized nanoparticles in a quartz-crystal microbalance-based immunosensor for the detection of parathion

BACKGROUND

Biosensor-based detection provides a rapid and low-cost alternative to conventional analytical methods for revealing the presence of the contaminants in water as well as solid matrices. Although important to be detected, small analytes (few hundreds of Daltons) are an issue in biosensing since the signal they induce in the transducer, and specifically in a Quartz-Crystal Microbalance, is undetectable. A pesticide like parathion (M = 292 Da) is a typical example of contaminant for which a signal amplification procedure is desirable.

METHODS/FINDINGS

The ballasting of the analyte by gold nanoparticles has been already applied to heavy target as proteins or bacteria to improve the limit of detection. In this paper, we extend the application of such a method to small analytes by showing that once the working surface of a Quartz-Crystal Microbalance (QCM) has been properly functionalized, a limit of detection lower than 1 ppb is reached for parathion. The effective surface functionalization is achieved by immobilizing antibodies upright oriented on the QCM gold surface by a simple photochemical technique (Photonic Immobilization Technique, PIT) based on the UV irradiation of the antibodies, whereas a simple protocol provided by the manufacturer is applied to functionalize the gold nanoparticles. Thus, in a non-competitive approach, the small analyte is made detectable by weighing it down through a "sandwich protocol" with a second antibody tethered to heavy gold nanoparticles. The immunosensor has been proved to be effective against the parathion while showing no cross reaction when a mixture of compounds very similar to parathion is analyzed.

CONCLUSION/SIGNIFICANCE

The immunosensor described in this paper can be easily applied to any small molecule for which polyclonal antibodies are available since both the functionalization procedure of the QCM probe surface and gold nanoparticle can be applied to any IgG, thereby making our device of general application in terms of target analyte.

NFAP2, a novel cysteine-rich anti-yeast protein from Neosartorya fischeri NRRL 181: isolation and characterization

The increasing incidence of fungal infections and damages due to drug-resistant fungi urges the development of new antifungal strategies. The cysteine-rich antifungal proteins from filamentous ascomycetes provide a feasible base for protection against molds due to their potent antifungal activity on them. In contrast to this, they show no or weak activity on yeasts, hence their applicability against this group of fungi is questionable. In the present study a 5.6 kDa anti-yeast protein (NFAP2) is isolated, identified and characterized from the ferment broth of Neosartorya fischeri NRRL 181. Based on a phylogenetic analysis, NFAP2 and its putative homologs represent a new group of ascomycetous cysteine-rich antifungal proteins. NFAP2 proved to be highly effective against tested yeasts involving clinically relevant Candida species. NFAP2 did not cause metabolic inactivity and apoptosis induction, but its plasma membrane disruption ability was observed on Saccharomyces cerevisiae. The antifungal activity was maintained after high temperature treatment presumably due to the in silico predicted stable tertiary structure. The disulfide bond-stabilized, heat-resistant folded structure of NFAP2 was experimentally proved. After further investigations of antifungal mechanism, structure and toxicity, NFAP2 could be applicable as a potent antifungal agent against yeasts.

A Penicillium chrysogenum-based expression system for the production of small, cysteine-rich antifungal proteins for structural and functional analyses

Background

Small, cysteine-rich and cationic antifungal proteins (APs) from filamentous ascomycetes, such as NFAP from Neosartorya fischeri and PAF from Penicillium chrysogenum, are promising candidates for novel drug development. A prerequisite for their application is a detailed knowledge about their structure–function relation and mode of action, which would allow protein modelling to enhance their toxicity and specificity. Technologies for structure analyses, such as electronic circular dichroism (ECD) or NMR spectroscopy, require highly purified samples and in case of NMR milligrams of uniformly ¹⁵N-/¹³C-isotope labelled protein. To meet these requirements, we developed a P. chrysogenum-based expression system that ensures sufficient amount and optimal purity of APs for structural and functional analyses.

Results

The APs PAF, PAF mutants and NFAP were expressed in a P. chrysogenum ∆paf mutant strain that served as perfect microbial expression factory. This strain lacks the paf-gene coding for the endogenous antifungal PAF and is resistant towards several APs from other ascomycetes. The expression of the recombinant proteins was under the regulation of the strong paf promoter, and the presence of a paf-specific pre-pro sequence warranted the secretion of processed proteins into the supernatant. The use of defined minimal medium allowed a single-step purification of the recombinant proteins. The expression system could be extended to express PAF in the related fungus Penicillium digitatum, which does not produce detectable amounts of APs, demonstrating the versatility of the approach. The molecular masses, folded structures and antifungal activity of the recombinant proteins were analysed by ESI–MS, ECD and NMR spectroscopy and growth inhibition assays.

Conclusion

This study demonstrates the implementation of a paf promoter driven expression cassettes for the production of cysteine-rich, cationic, APs in different Penicillium species. The system is a perfect tool for the generation of correctly folded proteins with high quality for structure–function analyses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0586-4) contains supplementary material, which is available to authorized users.

EGF Functionalized Polymer-Coated Gold Nanoparticles Promote EGF Photostability and EGFR Internalization for Photothermal Therapy

The application of functionalized nanocarriers on photothermal therapy for cancer ablation has wide interest. The success of this application depends on the therapeutic efficiency and biocompatibility of the system, but also on the stability and biorecognition of the conjugated protein. This study aims at investigating the hypothesis that EGF functionalized polymer-coated gold nanoparticles promote EGF photostability and EGFR internalization, making these conjugated particles suitable for photothermal therapy. The conjugated gold nanoparticles (100–200 nm) showed a plasmon absorption band located within the near-infrared range (650–900 nm), optimal for photothermal therapy applications. The effects of temperature, of polymer-coated gold nanoparticles and of UVB light (295nm) on the fluorescence properties of EGF have been investigated with steady-state and time-resolved fluorescence spectroscopy. The fluorescence properties of EGF, including the formation of Trp and Tyr photoproducts, is modulated by temperature and by the intensity of the excitation light. The presence of polymeric-coated gold nanoparticles reduced or even avoided the formation of Trp and Tyr photoproducts when EGF is exposed to UVB light, protecting this way the structure and function of EGF. Cytotoxicity studies of conjugated nanoparticles carried out in normal-like human keratinocytes showed small, concentration dependent decreases in cell viability (0–25%). Moreover, conjugated nanoparticles could activate and induce the internalization of overexpressed Epidermal Growth Factor Receptor in human lung carcinoma cells. In conclusion, the gold nanoparticles conjugated with Epidermal Growth Factor and coated with biopolymers developed in this work, show a potential application for near infrared photothermal therapy, which may efficiently destroy solid tumours, reducing the damage of the healthy tissue.

Single Molecule Characterization of UV-Activated Antibodies on Gold by Atomic Force Microscopy

The interaction between proteins and solid surfaces can influence their conformation and therefore also their activity and affinity. These interactions are highly specific for the respective combination of proteins and solids. Consequently, it is desirable to investigate the conformation of proteins on technical surfaces, ideally at single molecule level, and to correlate the results with their activity. This is in particular true for biosensors where the conformation-dependent target affinity of an immobilized receptor determines the sensitivity of the sensor. Here, we investigate for the first time the immobilization and orientation of antibodies (Abs) photoactivated by a photonic immobilization technique (PIT), which has previously demonstrated to enhance binding capabilities of antibody receptors. The photoactivated immunoglobulins are immobilized on ultrasmooth template stripped gold films and investigated by atomic force microscopy (AFM) at the level of individual molecules. The observed protein orientations are compared with results of nonactivated antibodies adsorbed on similar gold films and mica reference samples. We find that the behavior of Abs is similar for mica and gold when the protein are not treated (physisorption), whereas smaller contact area and larger heights are measured when Abs are treated (PIT). This is explained by assuming that the activated antibodies tend to be more upright compared with nonirradiated ones, thereby providing a better exposure of the binding sites. This finding matches the observed enhancement of Abs binding efficiency when PIT is used to functionalize gold surface of QCM-based biosensors.

Lysozyme Photochemistry as a Function of Temperature. The Protective Effect of Nanoparticles on Lysozyme Photostability

The presence of aromatic residues and their close spatial proximity to disulphide bridges makes hen egg white lysozyme labile to UV excitation. UVB induced photo-oxidation of tryptophan and tyrosine residues leads to photochemical products, such as, kynurenine, N-formylkynurenine and dityrosine and to the disruption of disulphide bridges in proteins. We here report that lysozyme UV induced photochemistry is modulated by temperature, excitation power, illumination time, excitation wavelength and by the presence of plasmonic quencher surfaces, such as gold, and by the presence of natural fluorescence quenchers, such as hyaluronic acid and oleic acid. We show evidence that the photo-oxidation effects triggered by 295 nm at 20°C are reversible and non-reversible at 10°C, 25°C and 30°C. This paper provides evidence that the 295 nm damage threshold of lysozyme lies between 0.1 μW and 0.3 μW. Protein conformational changes induced by temperature and UV light have been detected upon monitoring changes in the fluorescence emission spectra of lysozyme tryptophan residues and SYPRO® Orange. Lysozyme has been conjugated onto gold nanoparticles, coated with hyaluronic acid and oleic acid (HAOA). Steady state and time resolved fluorescence studies of free and conjugated lysozyme onto HAOA gold nanoparticles reveals that the presence of the polymer decreased the rate of the observed photochemical reactions and induced a preference for short fluorescence decay lifetimes. Size and surface charge of the HAOA gold nanoparticles have been determined by dynamic light scattering and zeta potential measurements. TEM analysis of the particles confirms the presence of a gold core surrounded by a HAOA matrix. We conclude that HAOA gold nanoparticles may efficiently protect lysozyme from the photochemical effects of UVB light and this nanocarrier could be potentially applied to other proteins with clinical relevance. In addition, this study confirms that the temperature plays a critical role in the photochemical pathways a protein enters upon UV excitation.

Elucidation of ultraviolet radiation-induced cell responses and intracellular biomolecular dynamics in mammalian cells using surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy has been used to elucidate biomolecular dynamics on the response of mammalian cells towards UV light irradiation.

Fingerprinting biochemical changes associated with cellular responses to external stimuli can provide vital information on the dynamics of biological processes and their defense mechanisms. In this study, surface-enhanced Raman spectroscopy (SERS) has been used to elucidate biomolecular dynamics on the response of healthy and cancerous cells towards ultraviolet (UV) light irradiation at the cellular level in real-time. We have identified a number of physiochemical damages to proteins, especially to the chemical structure of the sulfur and aromatic amino acid containing moieties, as well as changes in secondary structure. Furthermore, we found that continuous exposure of short wave UV-C light (254 nm) to living cells can photolytically damage intracellular proteins and can completely arrest nanoparticle transport and trigger apoptosis. However, under similar conditions, this was not observed when the cells were exposed to long wave UV-A light (365 nm). These biomolecular events were probed in real-time using SERS and dark-field (DF) imaging. Specifically, this technique has been utilized for the real-time evaluation of a unique cellular defense mechanism in cancer cells towards UV exposure. Our technique provides a powerful approach to understand the mechanisms of UV light-triggered cell death, protein dynamics, and enhanced cell repair and defense machinery within cancer cells through actively monitoring molecular vibrations.

The feasibility of coherent energy transfer in microtubules

It was once purported that biological systems were far too 'warm and wet' to support quantum phenomena mainly owing to thermal effects disrupting quantum coherence. However, recent experimental results and theoretical analyses have shown that thermal energy may assist, rather than disrupt, quantum coherent transport, especially in the 'dry' hydrophobic interiors of biomolecules. Specifically, evidence has been accumulating for the necessary involvement of quantum coherent energy transfer between uniquely arranged chromophores in light harvesting photosynthetic complexes. The 'tubulin' subunit proteins, which comprise microtubules, also possess a distinct architecture of chromophores, namely aromatic amino acids, including tryptophan. The geometry and dipolar properties of these aromatics are similar to those found in photosynthetic units indicating that tubulin may support coherent energy transfer. Tubulin aggregated into microtubule geometric lattices may support such energy transfer, which could be important for biological signalling and communication essential to living processes. Here, we perform a computational investigation of energy transfer between chromophoric amino acids in tubulin via dipole excitations coupled to the surrounding thermal environment. We present the spatial structure and energetic properties of the tryptophan residues in the microtubule constituent protein tubulin. Plausibility arguments for the conditions favouring a quantum mechanism of signal propagation along a microtubule are provided. Overall, we find that coherent energy transfer in tubulin and microtubules is biologically feasible.

Enhanced Light Absorption in Porous Particles for Ultra-NIR-Sensitive Biomaterials

Conducting polymers with the capability of photothermal conversion extend the application of near-infrared light (NIR), satisfying the demands of less toxicity, easy availability, and high flexibility for NIR-sensitive materials. The improvement of light use efficiency is still urgent and challenging. In this work, an ultra-NIR-sensitive biocompatible porous particle composed of a polylactic acid matrix and polypyrrole nanoparticles is prepared via a one-step double-emulsion method. It is revealed that the light absorption of polyprryole is effectively improved within the porous structure. This particle is exploited as a cost-effective sensing material in terms of its conductivity change for preparing paper-based NIR light sensors. Moreover, the microspheres act as a guardian to encapsulate and lock excess nucleic acids which is useful for preventing inflammatory diseases.

Keeping time: could quantum beating in microtubules be the basis for the neural synchrony related to consciousness?

This paper discusses the possibility of quantum coherent oscillations playing a role in neuronal signaling. Consciousness correlates strongly with coherent neural oscillations, however the mechanisms by which neurons synchronize are not fully elucidated. Recent experimental evidence of quantum beats in light-harvesting complexes of plants (LHCII) and bacteria provided a stimulus for seeking similar effects in important structures found in animal cells, especially in neurons. We argue that microtubules (MTs), which play critical roles in all eukaryotic cells, possess structural and functional characteristics that are consistent with quantum coherent excitations in the aromatic groups of their tryptophan residues. Furthermore we outline the consequences of these findings on neuronal processes including the emergence of consciousness.

Photonic activation of plasminogen induced by low dose UVB

Activation of plasminogen to its active form plasmin is essential for several key mechanisms, including the dissolution of blood clots. Activation occurs naturally via enzymatic proteolysis. We report that activation can be achieved with 280 nm light. A 2.6 fold increase in proteolytic activity was observed after 10 min illumination of human plasminogen. Irradiance levels used are in the same order of magnitude of the UVB solar irradiance. Activation is correlated with light induced disruption of disulphide bridges upon UVB excitation of the aromatic residues and with the formation of photochemical products, e.g. dityrosine and N-formylkynurenine. Most of the protein fold is maintained after 10 min illumination since no major changes are observed in the near-UV CD spectrum. Far-UV CD shows loss of secondary structure after illumination (33.4% signal loss at 206 nm). Thermal unfolding CD studies show that plasminogen retains a native like cooperative transition at ~70 ºC after UV-illumination. We propose that UVB activation of plasminogen occurs upon photo-cleavage of a functional allosteric disulphide bond, Cys737-Cys765, located in the catalytic domain and in van der Waals contact with Trp761 (4.3 Å). Such proximity makes its disruption very likely, which may occur upon electron transfer from excited Trp761. Reduction of Cys737-Cys765 will result in likely conformational changes in the catalytic site. Molecular dynamics simulations reveal that reduction of Cys737-Cys765 in plasminogen leads to an increase of the fluctuations of loop 760–765, the S1-entrance frame located close to the active site. These fluctuations affect the range of solvent exposure of the catalytic triad, particularly of Asp646 and Ser74, which acquire an exposure profile similar to the values in plasmin. The presented photonic mechanism of plasminogen activation has the potential to be used in clinical applications, possibly together with other enzymatic treatments for the elimination of blood clots.

Modulating the structure of EGFR with UV light: new possibilities in cancer therapy

The epidermal growth factor receptor (EGFR) is a member of the ErbB family of receptor tyrosine kinases. EGFR is activated upon binding to e.g. epidermal growth factor (EGF), leading to cell survival, proliferation and migration. EGFR overactivation is associated with tumor progression. We have previously shown that low dose UVB illumination of cancer cells overexpressing EGFR prior to adding EGF halted the EGFR signaling pathway. We here show that UVB illumination of the extracellular domain of EGFR (sEGFR) induces protein conformational changes, disulphide bridge breakage and formation of tryptophan and tyrosine photoproducts such as dityrosine, N-formylkynurenine and kynurenine. Fluorescence spectroscopy, circular dichroism and thermal studies confirm the occurrence of conformational changes. An immunoassay has confirmed that UVB light induces structural changes in the EGF binding site. A monoclonal antibody which competes with EGF for binding sEGFR was used. We report clear evidence that UVB light induces structural changes in EGFR that impairs the correct binding of an EGFR specific antibody that competes with EGF for binding EGFR, confirming that the 3D structure of the EGFR binding domain suffered conformational changes upon UV illumination. The irradiance used is in the same order of magnitude as the integrated intensity in the solar UVB range. The new photonic technology disables a key receptor and is most likely applicable to the treatment of various types of cancer, alone or in combination with other therapies.

The binding behavior of itraconazole with hemoglobin: studies from multi-spectroscopic techniques

The interactions between hemoglobin (Hb) and itraconazole (ITZ) are investigated in details using UV-vis spectra, circular dichroism spectroscopy, steady state fluorescence, three-dimensional fluorescence spectra, synchronous fluorescence and time-resolved fluorescence spectra at molecular level. The UV-vis studies represent that ITZ can access into heme group and lead to it explored in aqueous medium. CD spectra suggest ITZ could combine with amino acid residues in polypeptide chain and cause a partial unfolding of Hb (reducing of the α-helix content). Steady state fluorescence/synchronous fluorescence (taking into account inner filter effects) and three-dimensional fluorescence/time-resolved fluorescence spectroscopy results reveal that ITZ alters polarity and conformation around the fluorophore molecule. The interaction processes are static quenching mechanisms. The negative of ΔH(0) and ΔS(0) indicate that hydrogen bonds and van der Waals are the main force.

Photodegradation of human growth hormone: a novel backbone cleavage between Glu-88 and Pro-89

The exposure of protein pharmaceuticals to light can cause loss of potency, oxidation, structural changes and aggregation. To elucidate the chemical pathways of photodegradation, we irradiated human growth hormone (hGH) at λ = 254 nm, λ ≈ 265-340 nm, and λ ≈ 295-340 nm (using the spectral cutoff of borosilicate glass) and analyzed the products by mass spectrometry. By means of LC-MS/MS analysis, we observed an unusual peptide backbone cleavage between Glu-88 and Pro-89. The crystal structure of hGH indicates that these residues are in proximity to Trp-86, which likely mediates this backbone cleavage. The two cleavage fragments observed by MS/MS analysis indicate the loss of CO from the amide bond and replacement of the Glu-C(═ O)Pro bond with a Glu-H bond, accompanied by double bond formation on proline. The reaction is oxygen-independent and likely involves hydrogen transfer to the Cα of Glu-88. To probe the influence of the protein fold, we irradiated hGH in its unfolded state, in 1:1 (v/v) acetonitrile/water, and also the isolated tryptic peptide Ile-78-Arg-90, which contains the Glu-88-Pro-89 sequence. In both cases, the cleavage between Glu-88 and Pro-89 was largely suppressed, while other cleavage pathways became dominant, notably between Gln-84 and Ser-85, as well as Ser-85 and Trp-86.