Strong Hydrophobic Interactions Research Articles

A π-Stacking Based Fluorescent Probe for Labeling of Flavin Analogues in Live Cells through Unusual FRET Process.

The flavin adenine dinucleotide (FAD) is an indispensable coenzyme in live cells. It acts as a catalyst in many redox responsive metabolic reactions, including oxidative phosphorylation in mitochondria. The real-time monitoring of flavin is important to understand the disorder in the metabolic process, redox system, etc. Thus, we have developed a fluorescent probe CPy-1 that noncovalently binds with flavin to exhibit the FRET process. 1H- NMR and docking study indicated that there is a strong hydrophobic interaction between flavins and CPy-1. Also, a π-π stacking between isoalloxazine ring in flavin and quinoline and coumarin moieties of CPy-1 favors self-assembly. The nontoxic probe CPy-1 could distinguish cancer cells from normal cells based on expressions of endogenous FAD.

Efficacy of defensins as neutralizing agents against the deadly SARS-CoV-2

SARS-CoV-2 infection causes asymptomatic to severe human respiratory diseases. Vaccinations are effective only to a certain extent, and the disease recurs with milder symptoms even after booster doses. Hence, we hypothesize that antiviral therapy in conjunction with vaccination is the need of the hour for containing the disease. SARS-CoV-2 enters the host cell through interaction between viral spike (S) protein and human Angiotensin II converting enzyme2 (ACE2). So, any S-protein neutralizing molecule could be a potential antiviral moiety. The interaction-interface architecture indicates that cationic peptides effectively bind to anionic interface residues of S protein-receptor binding domain (S-RBD). Subsequently, we adopted molecular docking and simulation approaches to examine the binding affinity of cationic human α and β defensins, HNP1 and HBD2 with S-RBD. We observed strong hydrogen bonds, electrostatic, salt bridge, and hydrophobic interactions between these defensins and S-RBD with binding energy (BE) of −10.7 kcal/mol. Interestingly, defensins from Zea mays (ZmD32), Solanum lycopersicum (TPP3), and Sorghum bicolor (DEF1_SORBI) exhibited approximately similar BE of −11.1 kcal/mol, −11.9 kcal/mol, and −12.6 kcal/mol respectively, comparable to ACE2 (BE= −11.9 kcal/mol). Molecular dynamics simulation of S-RBD complexes formed with HBD2, ZmD32 and TPP3, showed stable associations for 100 ns. Results of in-silico studies demonstrated higher binding affinity of more positively-charged peptides with S-RBD, suggesting the potential of plant defensins to block ACE2 binding of S-RBD. These results warrant experimental validation. However these findings indicate the usefulness of plant defensin homologues as neutralizing antiviral agents for use as ideal prophylactic and therapeutic drugs for COVID-19. Communicated by Ramaswamy H. Sarma

Molecular Basis of the Reinforced Effect of Berberine against Cutinase from Colletotrichum capsisi by Supplying Sodium Stearate as Dispersant.

Berberine (BBR) is a promising botanical pesticide that can reduce the enzyme activity of secreted cutinase from fungal pathogens. However, only less than 15% of total activity was prohibited. Herein we researched BBR's self-aggregation in water via molecular dynamics simulations, and further investigated the effect of dispersant on blocking the aggregation together with the impact on cutinase. Strong hydrophobic interactions were found between adjacent BBR molecules, and these molecules formed clustered conformations at different BBR concentrations. Interestingly, one of the tested dispersants, sodium stearate (ST), is able to insert into BBR clusters and form stable interaction until the end of simulation, resulting in decreased hydrophobic strength in the BBR-ST cluster. More importantly, supply of ST with BBR resulted in BBR's reinforced hydrophobic interactions between BBR and the catalytic center of cutinase, which led to the inactivated mode of cutinase. Finally, wet experiments demonstrated that combined application of BBR and ST indeed resulted in a synergy-like effect on reducing the activity of cutinase. Overall, our findings revealed the mechanism of the reinforced effect of BBR against cutinase when supplying ST as dispersant, suggesting an undiscovered role of ST in enhancing the efficiency of this botanical pesticide.

Sulfonate‐Functionalized AIEgens: Strategic Approaches Beyond Water Solubility for Sensing and Imaging Applications

AbstractThe development of water‐soluble aggregation‐induced emission (AIE)‐active “light‐up” probes for sensing and imaging purposes has drawn immense research attention in the recent past. One strategy has been to introduce −SO3− groups in AIEgens (AIE‐sulfonates) to increase their hydrophilic properties, and the ionic nature of the corresponding compounds also paves the way for electrostatic interaction with various analytes, in particular, with several biospecies having positively charged surfaces. A significant number of AIE‐sulfonates, many among them having a tetraphenylethylene (TPE) moiety, have been designed and synthesized for the selective detection of a variety of analytes, such as metal ions, small molecules, enzymes, proteins, and bacteria. The strategies for selective detection include, for example, spontaneous complex formation with cations, electrostatic interaction with target‐specific units in the biospecies, and strong hydrophobic interactions. In addition, these AIEgens are used in cell imaging and OLED applications. This Review attempts to provide a summary and discuss recent developments in sulfonate‐functionalized AIE‐active “light‐up” probes in sensing and imaging applications with a focus on the role of the sulfonate functionality in the design and sensing processes.

Preparation of fat substitute based on the high-methoxyl pectin of citrus and application in moon-cake skin

The high-methoxyl pectin of citrus was used to prepare a fat substitute and applied to the processing technology of moon-cake skin. The physical, chemical, and sensory properties of fat substitutes and prepared moon-cake skins were studied by selecting texture properties, rheological properties, water distribution, and water-holding capacity. Results showed that the gel hardness of glucan–sucrose (G-SG) (glucan/sucrose = 4:6) as synergistic gel was 6.23 ± 0.10 N, the elasticity was 3.97 ± 0.03 mm, the adhesive viscosity was 4.87 ± 0.20 N, the chewiness was 16.87 ± 0.51 mj, the water-holding capacity was 98.33%, and the gel obtained from sucrose (SG) as gelation agent had no significant difference (P > 0.05). The consistency coefficient and thixotropic circle area of G-SG was larger than that of SG. Through dynamic viscoelastic scanning, we found that the tanδ of G-SG was smaller, and it had stronger hydrophobic interaction and stronger fluid properties after high-speed shear. It also more easily maintained a flow state similar to oil. G-SG was further applied to the processing technology of low-fat moon-cake skin. The color of the prepared low-fat moon-cake skin darkened, the water-holding capacity was enhanced, the fat content decreased from 22.21% ± 0.54% to 14.07% ± 0.57%, the oil droplets enlarged, and flocculation strengthened. Results of texture-characteristic and sensory-score analyses showed no significant difference (P > 0.05) from the control group when the oil substitution amount was 40%. At this time, the total sensory score was 41.71 ± 2.02.

1,2,3-Triazole derivatives as highly selective cannabinoid receptor type 2 (CB2) agonists

The cannabinoid receptor 2 (CB2 receptor) has attracted considerable interest, mainly due to its potential as a target for therapeutics for treating various diseases that have a neuroinflammatory or neurodegenerative component while avoiding the adverse psychotropic effects that accompany CB1 receptor-based therapies. With the appreciation that CB2-selective ligands show marked functional selectivity, there is a renewed opportunity to explore this promising area of research from both a mechanistic as well as a therapeutic perspective. In this research, we are interested in the discovery of new chemotypes as highly selective CB2 modulators, which may serve as good starting points for further optimization towards the development of CB2 therapeutics. In search of new chemotypes as CB2 selective agents, we screened a series of triazole derivatives with interesting bioactive scaffolds, which led to the discovery of two novel and highly selective ligands for CB2 receptors. Compounds 6 and 11 produced a concentration-dependent inhibition of specific [3H]-CP55,940 (CB2) binding with Ki ± SEM values of 105.3 ± 22.6 and 116.4 ± 19.5 nM, respectively, while no binding affinity towards CB1 receptors or opioid receptors was observed. The CB2 functional activity of 6 and 11, as measured by a GPCR Tango assay (G-protein independent β-arrestin translocation assay), revealed that these compounds act as CB2 agonists with EC50 values ± SEM of 1.83 ± 0.16 and 1.14 ± 0.52 µM, respectively. Molecular modeling results showed that both compounds fit well into the active site of the CB2 receptor and showed strong hydrophobic interactions with key residues. In conclusion, the new triazole derivatives (6 and 11) showed promising activity towards CB2 receptors and have great potential to be developed into therapeutically useful CB2 agonists through hit-to-lead optimization.

Influence of solvent polarity of ethonal/water binary solvent on the structural, emulsifying, interfacial rheology properties of gliadin nanoparticles

Gliadin nanoparticles (GNPs) is a promising material for stabilizing Pickering emulsions. The present work aimed to investigate the effect of solvent polarity of ethonal/water binary solvent on the structure and emulsifying property of GNPs and provide reference information for the potential application of GNPs in alcoholic food system. The structural, emulsifying and interfacial rheology properties of GNPs in aqueous phases with different polarity (EN(T):1.00–0.94) were evaluated. The solvent polarity was regulated by changing the ethanol concentration in aqueous phase. Results showed that the emulsifying activity of GNPs significantly improved as the EN(T) decreased from 1.00 to 0.96, and then decreased as the EN(T) further decreased from 0.96 to 0.94 for the rising particle size. Meanwhile, the decrease of solvent polarity improved the diffusion rate, viscoelastic modulus (E) and the interparticle interaction of GNPs. The possible mechanism was investigated by discussing the relationship among the structural, emulsifying and interfacial rheology properties of GNPs. It was found that the decrease of solvent polarity triggered the increase of hydrophobic groups distributed on the particle surface, and then resulted in the decrease of zeta potential and the increase of surface hydrophobicity of GNPs, which benefited the diffusion/adsorption of particles and the formation of viscoelastic protein layers for lower electrostatic repulsion, moderate surface wettability and stronger hydrophobic interaction. The results also suggested that GNPs might be a natural and economical material for low-degree alcohol emulsion food.

Polymer-Surfactant Driven Interactions and the Resultant Microstructure in Protein-Containing Liquid Crystal Droplets.

Integration of molecular liquid crystals (LCs) with functional proteins can provide new class of materials for potential applications in optical biosensing. However, hydrophobic nematic LCs (length ∼ 1-2 nm) and hydrophilic proteins, size ∼ O (nm), do not intermix without chemical modification of at least one of them. Bioconjugation of proteins with a polyethylene glycol-based polymeric surfactant (PS) can provide a core-shell system that is sequestered within nonaqueous LC (4-cyano-4'-pentylbiphenyl) microdroplets. However, the nature of interactions between the components and detailed understanding of the resultant hybrid microstructure remains unclear. Here, using a combination of isothermal titration calorimetry (ITC), fluorescence microscopy, and infrared-imaging spectroscopy, we show that strong hydrophobic interactions between the LC and PS drives the sequestration of a myoglobin-PS (Mb-PS; dispersed in the aqueous phase) into the LC spherical microdroplets or even into a bulk LC phase. The average values of both, the binding constant and the standard molar enthalpy change, are increased by approximately a factor of 2.5 times when the unmodified Mb is conjugated to the PS. Small-angle X-ray scattering studies reveal that LC molecules act as a solvent for the Mb-PS conjugate; furthermore, the LC long-range order is disturbed due to mixing, as exemplified by the change in its coherence length from 8.9 to 5.7 nm. Detailed all-atomistic molecular dynamic simulations for a three-component PS-water-LC system show a change in interaction energy of -144 kJ mol-1 PS-1 upon the contact of PS chains (initially dispersed in water) with LC and agree with the ITC experiments.

Bionanoscale Recognition Underlies Cell Fate and Therapy.

Understanding the bionanoscale recognition of nanostructured architectures is critical to the design and application of nanomaterials, but the related information is not well understood. In this study, it is found that bionanoscale recognition underlies cell fate and therapy. For example, 1T phase (octahedral coordination) monolayer MoS2 exhibits a markedly stronger affinity for fibronectin than the 2H structure (triangular prism coordination) and promotes cell spreading and differentiation. The van der Waals energy and increased turn components contribute to the high adhesion of fibronectin onto the 1T-MoS2 structure. 1T-MoS2 exhibits a significantly stronger affinity (KD , 6.59× 10-7 m) for liposomes than 2H-MoS2 (1.21× 10-6 m) due to strong hydrophobic interactions. The existence of octahedrally coordinated atomic structures that improve cell viability by enhancing the neurite length is first proven by random forest and structural equation models. Consequently, octahedral coordination disaggregates α-synuclein (e.g., by decreasing β-sheets and increasing coil structures) and protects cells and hosts against Parkinson's disease. As a proof-of-principle demonstration, these findings indicate that bionanoscale recognition underlies the design of biomaterials and cell therapeutics.

An account on the factors determining the extra stability of the β–hairpin from B1 domain of protein G

The folding–unfolding of a 16 residue polypeptide, a β–hairpin in B1 domain of protein G is investigated here to account for the factors assisting the extra stability of the polypeptide in the presence of an explicit solvent and even when a denaturant like urea is present in the medium. It is observed here that the backbone H–bond network well defines the folded state and is even capable of forming the folded state, but it is not the only criteria for making a stable β–hairpin fold. Factors such as the side chain H–bonds and the alignment of the certain hydrophobic group side chains play a prominent role in preserving the β–hairpin structure and thus providing an extra stability to the hairpin architecture. It is also affirmed that the mentioned hydrophobic groups side chain interactions are very crucial in holding the β–hairpin together and without which the hairpin collapses completely. We also confirm that the denaturant urea acts on the GB1–hairpin backbone H–bonds and in the presence of strong hydrophobic interactions with a consistent side chain H–bonding network, the denaturation being comparatively a slower process with respect to the protein devoid of the side chain interactions. Communicated by Ramaswamy H. Sarma

Reinforcing natural rubber by amphiphilic graphene oxide for high-performance catheters

Graphene oxide (GO) has been considered as a promising nanofiller to reinforce water-borne polymer due to its exceptional mechanical properties and good dispersibility in an aqueous solution. However, the re-aggregation of hydrophilic GO sheets in a hydrophobic polymer matrix with the evaporation of water, resulting from remarkable discrepancy of the interfacial energy, remains a significant challenge to achieve the high-performance GO-based polymer nanocomposites. Herein, the amphiphilic graphene oxide (AGO) rather than the conventional GO is applied to enhance the mechanical properties of natural rubber latex (NRL) through simple solution blending. Our results show that the AGO demonstrates not only good dispersibility in the NRL aqueous solution but also strong hydrophobic interaction with the NRL particles. Benefiting from this amphiphilic character, the good dispersibility of AGO in the NRL matrix is realized after the oven-drying process, leading to a simultaneous enhancement in tensile strength (up to 35 MPa) and elongation at break (up to 1100%). In particular, it is found that the NRL tube, a kind of catheter, demonstrates a remarkable improvement in both blasting pressure, blasting volume with just a small amount addition of AGO (as less as 0.1%). This work provides a simple, green, and efficient route to fabricate high-performance polymer latex/graphene nanocomposites.

A highly sensitive, dual-readout assay based on self-assembly of two functional nanoparticles for homogeneous detection of protein biomarkers

Rapid, simple, and accurate quantitation of protein biomarkers is of great importance for biomedical diagnostics. Herein, we describe a dual-readout (colorimetric and potential) sensing strategy, which allows homogeneous detection of protein biomarkers with an ultrabroad detection range. To do so, two functional nanoparticles are prepared, including an antifouling magnetic nanoparticle (ANP) serving as a scaffold and a DNA-modified gold nanoparticle (DNA-GNP) used to generate both color and potential signal. In the presence of target protein, it will induce the conformation switch of DNA probes and thus mediate the assembly of two nanoparticles through strong hydrophobic interaction. Then, the resulting core-shell nanostructures can be analyzed by either optical or potential signal because of the self-assembly of highly negatively charged GNPs onto zwitterionic ANPs. The colorimetric mode enables simple, straightforward, and cost-effective detection of interferon-γ (IFN-γ) at nanomolar concentration by the naked eye. While plenty of negatively charged groups carried by DNA-GNPs can produce amplified potential signals, making the detection limit down to 78.8 fM. Compared with other reported strategies for IFN-γ detection, this homogeneous, dual-readout detection platform is composed just of two functional nanoparticles, providing a rather simple and low-cost method for cytokine assay.

A structural-based machine learning method to classify binding affinities between TCR and peptide-MHC complexes

The activation of T cells is triggered by the interactions of T cell receptors (TCRs) with their epitopes, which are peptides presented by major histocompatibility complex (MHC) on the surfaces of antigen presenting cells (APC). While each TCR can only recognize a specific subset from a large repertoire of peptide-MHC (pMHC) complexes, it is very often that peptides in this subset share little sequence similarity. This is known as the specificity and cross-reactivity of T cells, respectively. The binding affinities between different types of TCRs and pMHC are the major driving force to shape this specificity and cross-reactivity in T cell recognition. The binding affinities, furthermore, are determined by the sequence and structural properties at the interfaces between TCRs and pMHC. Fortunately, a wealth of data on binding and structures of TCR-pMHC interactions becomes publicly accessible in online resources, which offers us the opportunity to develop a random forest classifier for predicting the binding affinities between TCR and pMHC based on the structure of their complexes. Specifically, the structure and sequence of a given complex were projected onto a high-dimensional feature space as the input of the classifier, which was then trained by a large-scale benchmark dataset. Based on the cross-validation results, we found that our machine learning model can predict if the binding affinity of a given TCR-pMHC complex is stronger or weaker than a predefined threshold with an overall accuracy approximately around 75 %. The significance of our prediction was estimated by statistical analysis. Moreover, more than 60 % of binding affinities in the ATLAS database can be successfully classified into groups within the range of 2 kcal/mol. Additionally, we show that TCR-pMHC complexes with strong binding affinity prefer hydrophobic interactions between amino acids with large aromatic rings instead of electrostatic interactions. Our results therefore provide insights to design engineered TCRs which enhance the specificity for their targeted epitopes. Taken together, this method can serve as a useful addition to a suite of existing approaches which study binding between TCR and pMHC.

Molecular modelling of coat protein of the Groundnut bud necrosis tospovirus and its binding with Squalene as an antiviral agent: In vitro and in silico docking investigations

Bud blight disease caused by groundnut bud necrosis virus (GBNV) is a serious constraint in the cultivation of agricultural crops such as legumes, tomato, chilies, potato, cotton etc. Owing to the significant damage caused by GBNV, an attempt was made to identify suitable organic antiviral agents through molecular modelling of the nucleocapsid Coat Protein of GBNV; molecular docking and molecular dynamics that disclosed the interaction of the ligands viz., Squalene and Ganoderic acid-A with coat protein of GBNV. Invitro inhibitory effect of Squalene and Ganoderic acid-A was examined in comparison with different concentrations, against GBNV in cowpea plants under glasshouse condition. The different concentrations of Squalene (50, 100, 150, 250 and 500 ppm) tested in vitro resulted in reduction of lesion numbers (1.69 cm2) as well as reduced virus titre in co-inoculation spray. The present study suggests the antiviral activity of Squalene by effectively fitting into binding site of coat protein of GBNV with favourable hydrophilic as well as strong hydrophobic interactions thereby challenging and blocking the binding of viral replication RNA with coat protein and propagation. The present organic antiviral molecules will be helpful in development of suitable eco-friendly formulations to mitigate GBNV infection disease in plants.

Physicochemical study of dietary fiber methylcellulose and human intestinal bile salt micellar aggregates

The cellulose ether and bile salt mixed systems have a potential to alter the lipid digestion. The basic understanding of the aggregation process, interaction, and physicochemical properties of cellulose ether and bile salt is an essential topic of study. In this work, the interaction between simple dietary fiber methylcellulose (MC) and bile salt sodium deoxycholate (NaDC) has been studied using UV-Vis absorption, steady-state fluorescence intensity, fluorescence quenching, conductivity, light scattering, and zeta potential measurements. Fluorescence properties of hydrophobic probe pyrene were used to find the critical aggregation concentration (CAC), critical micellar concentration (CMC), and aggregation number (Nagg) of the MC/NaDC system. Using conventional conductivity method CAC, CMC, and thermodynamic parameters of micellization i.e. standard Gibbs free energy (∆Gmic0), standard entropy (∆Smic0), and standard enthalpy (∆Hmic0), was calculated to know the information regarding the nature of micellization of MC/NaDC mixed system. The size distribution and zeta potential study give an insight into MC/NaDC interaction before and after the CAC point. The strong hydrophobic interaction between cellulose ether MC and bile salt NaDC shows that this mixed system may have further implications in lipid digestion.

Computational Insight on the Interaction of Common Blood Proteins with Gold Nanoparticles.

Protein interactions with engineered gold nanoparticles (AuNPs) and the consequent formation of the protein corona are very relevant and poorly understood biological phenomena. The nanoparticle coverage affects protein binding modalities, and the adsorbed protein sites influence interactions with other macromolecules and cells. Here, we studied four common blood proteins, i.e., hemoglobin, serum albumin, α1-antiproteinase, and complement C3, interacting with AuNPs covered by hydrophobic 11-mercapto-1-undecanesulfonate (MUS). We use Molecular Dynamics and the Martini coarse−grained model to gain quantitative insight into the kinetics of the interaction, the physico-chemical characteristics of the binding site, and the nanoparticle adsorption capacity. Results show that proteins bind to MUS−capped AuNPs through strong hydrophobic interactions and that they adapt to the AuNP surfaces to maximize the contact surface, but no dramatic change in the secondary structure of the proteins is observed. We suggest a new method to calculate the maximum adsorption capacity of capped AuNPs based on the effective surface covered by each protein, which better represents the realistic behavior of these systems.

Purification, identification, and molecular mechanism of DPP-IV inhibitory peptides from defatted Antarctic krill powder.

Dipeptidyl peptidase-IV (DPP-IV) inhibitors can reduce the blood sugar levels of diabetic patients by preventing the rapid decomposition of incretin hormone and prolonging its physiological effects. In this study, DPP-IV inhibitory peptides FAGDDAPR and LAPPRGSL were isolated from defatted Antarctic krill powder (DAKP) protein by the sequential purification of ultrafiltration, gel filtration chromatography, and RP-HPLC, and IC50 values of the two peptides were 349.70±3.66μM and 461.14±0.87μM, respectively. The FAGDDAPR and LAPPRGSL were identified by LC-MS/MS method, and the molecular models of DPP-IV and the two peptides were further constructed by AutoDock Vina software, the results revealed that the inhibition activity of FAGDDAPR and LAPPRGSL was mainly attributed to the formation of strong hydrophobic interactions and hydrogen bonds with amino acids of DPP-IV. PRACTICAL APPLICATIONS: DAKP is an economical by-product produced in the production of krill oil and contains high-quality protein, but these products were mainly used as fish feed and had low utility value in the past. DPP-IV inhibitors are an efficacious drug employed in the treatment of hyperglycemia processes. However, these drugs can cause undesirable side effects. Thus, the development of new natural hypoglycemic drugs with low side effects is a valuable strategy to be applied in therapeutic interventions.

Structural Insights into Notum Covalent Inhibition.

The carboxylesterase Notum hydrolyzes a palmitoleate moiety from Wingless/Integrated(Wnt) ligands and deactivates Wnt signaling. Notum inhibitors can restore Wnt signaling which may be of therapeutic benefit for pathologies such as osteoporosis and Alzheimer’s disease. We report the identification of a novel class of covalent Notum inhibitors, 4-(indolin-1-yl)-4-oxobutanoate esters. High-resolution crystal structures of the Notum inhibitor complexes reveal a common covalent adduct formed between the nucleophile serine-232 and hydrolyzed butyric esters. The covalent interaction in solution was confirmed by mass spectrometry analysis. Inhibitory potencies vary depending on the warheads used. Mechanistically, the resulting acyl-enzyme intermediate carbonyl atom is positioned at an unfavorable angle for the approach of the active site water, which, combined with strong hydrophobic interactions with the enzyme pocket residues, hinders the intermediate from being further processed and results in covalent inhibition. These insights into Notum catalytic inhibition may guide development of more potent Notum inhibitors.

Structure of plant photosystem I-plastocyanin complex reveals strong hydrophobic interactions.

Photosystem I is defined as plastocyanin-ferredoxin oxidoreductase. Taking advantage of genetic engineering, kinetic analyses and cryo-EM, our data provide novel mechanistic insights into binding and electron transfer between PSI and Pc. Structural data at 2.74 Å resolution reveals strong hydrophobic interactions in the plant PSI–Pc ternary complex, leading to exclusion of water molecules from PsaA–PsaB/Pc interface once the PSI–Pc complex forms. Upon oxidation of Pc, a slight tilt of bound oxidized Pc allows water molecules to accommodate the space between Pc and PSI to drive Pc dissociation. Such a scenario is consistent with the six times larger dissociation constant of oxidized as compared with reduced Pc and mechanistically explains how this molecular machine optimized electron transfer for fast turnover.

Carbon-nanotube-supported POXA1b laccase and its hydrophobin chimera for oxygen reduction and picomolar phenol biosensing

The immobilization of POXA1b laccase and its hydrophobin-fused chimera was performed at pristine Multiwalled Carbon Nanotube (MWCNT) and MWCNT-modified electrodes by electrografting of a 2-diazoniumanthraquinone salt. The influence of the hydrophobin domain and the MWCNT functionalization with anthraquinone groups towards immobilization of laccase was compared by direct electrochemistry under O2 and electrochemical biosensing of phenols. The hydrophobin domain affords the stable dispersion of MWCNT in water/ethanol, while being detrimental to the direct electron transfer between POXA1b and the electrode. On the contrary, the stronger hydrophobic interactions between anthraquinone and laccase affords direct electrochemistry of POXA1b and enabled the design of a highly sensitive phenol biosensor, reaching a limit-of-detection (LOD) of 2 pM and sensitivity of 23,600 mA L mmol−1 cm−2 for catechol, and a LOD of 15 nM and sensitivity of 0.053 mA L mmol−1 cm−2 for dopamine.