Cytochrome c Provides an Electron-Funneling Antenna for Efficient Photocurrent Generation in a Reaction Center Biophotocathode

Functional Coupling of Biohybrid Photosynthetic Antennae and Reaction Center Complexes: Quantitative Comparison with Native Antennae

Light-harvesting (LH) complexes in photosynthetic organisms absorb photons within limited wavelength ranges over a broad solar spectrum. Extension of the LH wavelength has been realized by attaching artificial fluorophores to LH complexes (biohybrid LH complexes) for complementing the limited-wavelength regions. However, how efficiently such fluorophores in biohybrid LH complexes function to drive the photocatalytic reaction center (RC) has not been quantitatively evaluated, specifically in comparison with native LH antenna complexes. In this study, we prepared various biohybrid LH1-RC complexes (from Rhodopseudomonas palustris), to quantitatively evaluate the LH activity of the attached external chromophores through a photocurrent generation reaction by LH1-RC on an electrode. For a direct comparison of the LH activity among the LH chromophores that were examined, we introduced the k1 term, which represents the extent of the functional coupling of LH and the photochemical reactions in the RC. We determined that the hydrophobic fluorophore ATTO647N attached to LH1 possesses the highest LH activity among the examined hydrophilic fluorophores such as Alexa647, and its activity is comparable to that of native LH1(-RC). The LH activity of LH2 (from Rhodoblastus acidophilus strain 10050) and its biohybrid LH2s were examined for the comprehensive assessment of their LH activity.

Photoelectrochemistry of a photosystem I - Ferredoxin construct on ITO electrodes

In this study, photobioelectrodes based on a ferredoxin-modified photosystem I (PSI-Fd) from Thermosynechococcus vestitus have been prepared and characterized regarding the direct electron transfer between PSI-Fd and the electrode. The modified PSI with the covalently linked ferredoxin (Fd) on its stromal side has been immobilized on indium-tin-oxide (ITO) electrodes with a 3-dimensional inverse-opal structure. Compared to native PSI, a lower photocurrent and a lower onset potential of the cathodic photocurrent have been observed. This can be mainly attributed to a different adsorption behavior of the PSI-Fd-construct onto the 3D ITO. However, the overall behavior is rather similar to PSI. First experiments have been performed for applying this PSI-Fd photobioelectrode for enzyme-driven NADPH generation. By coupling the electrode system with ferredoxin-NADP+-reductase (FNR), first hints for the usage of photoelectrons for biosynthesis have been collected by verifying NADPH generation.

Supramolecular Biohybrid Construct for Photoconversion Based on a Bacterial Reaction Center Covalently Bound to Cytochrome c by an Organic Light Harvesting Bridge

A supramolecular construct for solar energy conversion is developed by covalently bridging the reaction center (RC) from the photosynthetic bacterium Rhodobacter sphaeroides and cytochrome c (Cyt c) proteins with a tailored organic light harvesting antenna (hCy2). The RC-hCy2-Cyt c biohybrid mimics the working mechanism of biological assemblies located in the bacterial cell membrane to convert sunlight into metabolic energy. hCy2 collects visible light and transfers energy to the RC, increasing the rate of photocycle between a RC and Cyt c that are linked in such a way that enhances proximity without preventing protein mobility. The biohybrid obtained with average 1 RC/10 hCy2/1.5 Cyt c molar ratio features an almost doubled photoactivity versus the pristine RC upon illumination at 660 nm, and ∼10 times higher photocurrent versus an equimolar mixture of the unbound proteins. Our results represent an interesting insight into photoenzyme chemical manipulation, opening the way to new eco-sustainable systems for biophotovoltaics.

The Role of Electrostatic Binding Interfaces in the Performance of Bacterial Reaction Center Biophotoelectrodes

Photosynthetic reaction centers (RCs) efficiently capture and convert solar radiation into electrochemical energy. Accordingly, RCs have the potential as components in biophotovoltaics, biofuel cells, and biosensors. Recent biophotoelectrodes containing the RC from the bacterium Rhodobacter sphaeroides utilize a natural electron donor, horse heart cytochrome c (cyt c), as an electron transfer mediator with the electrode. In this system, electrostatic interfaces largely control the protein-electrode and protein-protein interactions necessary for electron transfer. However, recent studies have revealed kinetic bottlenecks in cyt-mediated electron transfer that limit biohybrid photoelectrode efficiency. Here, we seek to understand how changing protein-protein and protein-electrode interactions influence RC turnover and biophotoelectrode efficiency. The RC-cyt c binding interaction was modified by substituting interfacial RC amino acids. Substitutions Asn-M188 to Asp and Gln-L264 to Glu, which are known to produce a higher cyt-binding affinity, led to a decrease in the RC turnover frequency (TOF) at the electrode, suggesting that a decrease in cyt c dissociation was rate-limiting in these RC variants. Conversely, an Asp-M88 to Lys substitution producing a lower binding affinity had little effect on the RC TOF, suggesting that a decrease in the cyt c association rate was not a rate-limiting factor. Modulating the electrode surface with a self-assembled monolayer that oriented the cyt c to face the electrode did not affect the RC TOF, suggesting that the orientation of cyt c was also not a rate-limiting factor. Changing the ionic strength of the electrolyte solution had the most potent impact on the RC TOF, indicating that cyt c mobility was important for effective electron donation to the photo-oxidized RC. An ultimate limitation for the RC TOF was that cyt c desorbed from the electrode at ionic strengths above 120 mM, diluting its local concentration near the electrode-adsorbed RCs and resulting in poor biophotoelectrode performance. These findings will guide further tuning of these interfaces for improved performance.

Advancement of renewable energy technologies via artificial and microalgae photosynthesis

There has been an urgent need to tackle global climate change and replace conventional fuels with alternatives from sustainable sources. This has led to the emergence of bioenergy sources like biofuels and biohydrogen extracted from microalgae biomass. Microalgae takes up carbon dioxide and absorbs sunlight, as part of its photosynthesis process, for growth and producing useful compounds for renewable energy. While, the developments in artificial photosynthesis to a chemical process that biomimics the natural photosynthesis process to fix CO₂ in the air. However, the artificial photosynthesis technology is still being investigated for its implementation in large scale production. Microalgae photosynthesis can provide the same advantages as artificial photosynthesis, along with the prospect of having final microalgae products suitable for various application. There are significant potential to adapt either microalgae photosynthesis or artificial photosynthesis to reduce the CO₂ in the climate and contribute to a cleaner and green cultivation method.

Stabilisierung von Elektronentransferwegen erlaubt Stabilität von Biohybrid-Photoelektroden über Jahre

Die Nutzung natürlicher photosynthetischer Enzyme in biohybriden Anwendungen stellt eine attraktive und potenziell nachhaltige Möglichkeit zur Umwandlung von solarer Energie in Elektrizität und Brennstoffe dar. Jedoch begrenzt die Stabilität von photosynthetisch aktiven Proteinen nach der Implementierung in biohybride Anwendungsdesigns die operative Lebensdauer von Biophotoelektroden auf bisher wenige Stunden. In dieser Publikation demonstrieren wir, wie sich die Stabilität einer mesoporösen Elektrode, welche mit dem Photoprotein RC‐LH1 aus Rhodobacter sphaeroides beschichtet ist, erheblich steigern lässt. Durch die Aufrechterhaltung der Elektronenübertragungswege konnte die operative Lebensdauer unter Dauerlicht auf 33 Tage gesteigert werden und die operative Funktionalität nach einer Lagerung über mehr zwei Jahre hinweg demonstriert werden. Kombiniert mit hohen Photoströmen, die Spitzenwerte von 4.6 mA cm−2 erreichten, erzeugte die optimierte Biophotoelektrode eine kumulative Leistung von 86 C cm−2, die höchste bisher berichtete Leistung für diese Art von Elektroden. Unsere Ergebnisse zeigen, dass der Faktor, welcher die Stabilität einschränkt, die Architektur der Struktur ist, die das Photoprotein umgibt, sowie das entsprechende biohybride Sensoren und photovoltaische Geräte mit einer Betriebsdauer von mehreren Jahren möglich sind.

Sustaining Electron Transfer Pathways Extends Biohybrid Photoelectrode Stability to Years

The exploitation of natural photosynthetic enzymes in semi‐artificial devices constitutes an attractive and potentially sustainable route for the conversion of solar energy into electricity and solar fuels. However, the stability of photosynthetic proteins after incorporation in a biohybrid architecture typically limits the operational lifetime of biophotoelectrodes to a few hours. Here, we demonstrate ways to greatly enhance the stability of a mesoporous electrode coated with the RC‐LH1 photoprotein from Rhodobacter sphaeroides. By preserving electron transfer pathways, we extended operation under continuous high‐light to 33 days, and operation after storage to over two years. Coupled with large photocurrents that reached peak values of 4.6 mA cm⁻², the optimized biophotoelectrode produced a cumulative output of 86 C cm⁻², the largest reported performance to date. Our results demonstrate that the factor limiting stability is the architecture surrounding the photoprotein, and that biohybrid sensors and photovoltaic devices with operational lifetimes of years are feasible.

Supramolecular organization of Cytochrome-C into quantum-dot decorated macromolecular network under pH and thermal stress

The holo form of Cytochrome-C which is involved in the electron transfer chain of aerobic and anaerobic respiration remains structurally intact by its complex with heme. However, when a prolonged thermal and pH stress was applied, heme was found to abruptly dissociate from the holo protein, resulting in complete collapse of the three-dimensional functional structure. Interestingly, two distinct structures were formed as the consequence of the dissociation event: (i) A macromolecular amyloid-network formed by the collapsed protein fragments, generated by self-oxidation, and (ii) Fe-containing Quantum-Dots (FeQDs) with 2-3 nm diameter formed by heme reorganization. Further adding to intrigue, the FeQDs were re-adsorbed on the surface of the amyloid network leading to FeQD-decorated macromolecular amyloid matrix. The heme-interactant Met80, constituting the amyloidogenic region, initiates the amylogenic cascade, and gradual exposure of Trp59 synergistically emit intrinsic fluorescence alongside FeQDs. The development of the aforementioned events were probed through a multitude of biophysical, chemical and computational analyses like ThT/ANS/intrinsic fluorescence assays, CD-spectroscopy, FETEM/STEM/elemental mapping, Foldamyloid/Foldunfold/Isunstruct/H-protection/LIGplot analyses, etc. The FeQD-decorated amyloid-network was found to exhibit gel-like property, which supported the growth of BHK-21 fibroblast without cytotoxicity. Further studies on FeQD-decorated Cytochrome C amyloid network might open possibilities to design advanced biomaterial for diverse biological applications.

Photosynthetic Nanomaterial Hybrids for Bioelectricity and Renewable Energy Systems

Harvesting solar energy in the form of electricity from the photosynthesis of plants, algal cells, and bacteria has been researched as the most environment-friendly renewable energy technology in the last decade. The primary challenge has been the engineering of electrochemical interfacing with photosynthetic apparatuses, organelles, or whole cells. However, with the aid of low-dimensional nanomaterials, there have been many advances, including enhanced photon absorption, increased generation of photosynthetic electrons (PEs), and more efficient transfer of PEs to electrodes. These advances have demonstrated the possibility for the technology to advance to a new level. In this article, the fundamentals of photosynthesis are introduced. How PE harvesting systems have improved concerning solar energy absorption, PE production, and PE collection by electrodes is discussed. The review focuses on how different kinds of nanomaterials are applied and function in interfacing with photosynthetic materials for enhanced PE harvesting. Finally, the review analyzes how the performance of PE harvesting and stand-alone systems have evolved so far and its future prospects.

Electrospinning for building 3D structured photoactive biohybrid electrodes

We describe the development of biohybrid electrodes constructed via combination of electrospun (e-spun) 3D indium tin oxide (ITO) with the trimeric supercomplex photosystem I and the small electrochemically active protein cytochrome c (cyt c). The developed 3D surface of ITO has been created by electrospinning of a mixture of polyelthylene oxide (PEO) and ITO nanoparticles onto ITO glass slides followed by a subsequent elimination of PEO by sintering the composite. Whereas the photosystem I alone shows only small photocurrents at these 3D electrodes, the co-immobilization of cyt c to the e-spun 3D ITO results in well-defined photoelectrochemical signals. The scaling of thickness of the 3D ITO layers by controlling the time (10 min and 60 min) of electrospinning results in enhancement of the photocurrent. Several performance parameters of the electrode have been analyzed for different illumination intensities.

Design and Mechanism of a Self-Powered and Disintegration-Reorganization-Regeneration Power Supply with Cold Resistance

Up to now, power supplies designed based on the electrochemical reaction principle have had unavoidable defects, in that a complete redox reaction must be formed inside the power supply to operate normally, which makes it unable to be reconstructed and regenerated. Hence, the design and interpretation of this self-powered and disintegration-reorganization-regeneration power supply are generally considered to be almost insurmountable obstacles to haunt both experimenters and theorists. Herein, a self-powered and disintegration-reorganization-regeneration power supply with relatively stable discharge for 8.3 h is realized by the principle of ion-selective diffusion, which regenerates by radical polymerization. Additionally, the mechanism is investigated systematically by molecular dynamics simulation, and this power supply with a variety of self-powered and disintegration-reorganization-regeneration units can discharge continuously at freezing temperatures and variable temperature (0-25 °C). As a hypothetical model, a self-powered and deformable arch bridge with disintegration and reorganization is fabricated. In the future, this power supply is expected to be applied in prosthetic limbs, bionic skins, implantable power supplies, mobile phones, portable computers, wearable devices, etc. Moreover, with the improvement of the stability and discharge life, it could promote major revolutionary breakthroughs in the fields of intelligent industrial automation, smart buildings, intelligent transportation systems, intelligent power systems, etc.

Development of a universal conductive platform for anchoring photo- and electroactive proteins using organometallic terpyridine molecular wires

The construction of an efficient conductive interface between electrodes and electroactive proteins is a major challenge in the biosensor and bioelectrochemistry fields to achieve the desired nanodevice performance. Concomitantly, metallo-organic terpyridine wires have been extensively studied for their great ability to mediate electron transfer over a long-range distance. In this study, we report a novel stepwise bottom-up approach for assembling bioelectrodes based on a genetically modified model electroactive protein, cytochrome c553 (cyt c553) and an organometallic terpyridine (TPY) molecular wire self-assembled monolayer (SAM). Efficient anchoring of the TPY derivative (TPY-PO(OH)2) onto the ITO surface was achieved by optimising solvent composition. Uniform surface coverage with the electroactive protein was achieved by binding the cyt c553 molecules via the C-terminal His6-tag to the modified TPY macromolecules containing Earth abundant metallic redox centres. Photoelectrochemical characterisation demonstrates the crucial importance of the metal redox centre for the determination of the desired electron transfer properties between cyt and the ITO electrode. Even without the cyt protein, the ITO-TPY nanosystem reported here generates photocurrents whose densities are 2-fold higher that those reported earlier for ITO electrodes functionalised with the photoactive proteins such as photosystem I in the presence of an external mediator, and 30-fold higher than that of the pristine ITO. The universal chemical platform for anchoring and nanostructuring of (photo)electroactive proteins reported in this study provides a major advancement for the construction of efficient (bio)molecular systems requiring a high degree of precise supramolecular organisation as well as efficient charge transfer between (photo)redox-active molecular components and various types of electrode materials.

Correlating structural assemblies of photosynthetic reaction centers on a gold electrode and the photocurrent - potential response

The use of biomacromolecules is a nascent development in clean alternative energies. In applications of biosensors and biophotovoltaic devices, the bacterial photosynthetic reaction center (RC) is a protein-pigment complex that has been commonly interfaced with electrodes, in large part to take advantage of the long-lived and high efficiency of charge separation. We investigated assemblies of RCs on an electrode that range from monolayer to multilayers by measuring the photocurrent produced when illuminated by an intensity-modulated excitation light source. In addition, atomic force microscopy and modeling of the photocurrent with the Marcus-Hush-Chidsey theory detailed the reorganization energy for the electron transfer process, which also revealed changes in the RC local environment due to the adsorbed conformations. The local environment in which the RCs are embedded significantly influenced photocurrent generation, which has implications for electron transfer of other biomacromolecules deposited on a surface in sensor and photovoltaic applications employing a redox electrolyte.

Membrane Protein Modified Electrodes in Bioelectrocatalysis

Transmembrane proteins involved in metabolic redox reactions and photosynthesis catalyse a plethora of key energy-conversion processes and are thus of great interest for bioelectrocatalysis-based applications. The development of membrane protein modified electrodes has made it possible to efficiently exchange electrons between proteins and electrodes, allowing mechanistic studies and potentially applications in biofuels generation and energy conversion. Here, we summarise the most common electrode modification and their characterisation techniques for membrane proteins involved in biofuels conversion and semi-artificial photosynthesis. We discuss the challenges of applications of membrane protein modified electrodes for bioelectrocatalysis and comment on emerging methods and future directions, including recent advances in membrane protein reconstitution strategies and the development of microbial electrosynthesis and whole-cell semi-artificial photosynthesis.

Photoelectric Conversion System Composed of Gene-Recombined Photosystem I and Platinum Nanoparticle Nanosheet

Photosynthesis is one of the most vital processes in nature, which consists of two main photoreaction centers called photosystem I and photosystem II. The high quantum yield of photosystem I (PSI) makes it attractive for bioelectronic applications. However, the native PSI (N-PSI) loses its robust photochemical properties once fabricated into devices. This property degradation results from the difficulty in controlling the orientation of PSI. With the optimal orientation of PSI, photoexcited electrons can easily reach the electrode, yielding good photoelectric conversion efficiency. We developed a novel photoelectrode by integrating a newly designed gene-recombined PSI (G-PSI) with platinum nanoparticles (PtNPs) on substrates using a simple stacking method, which can control the orientation of PSI on the electrode. The target orientation of the attached G-PSI toward the substrate was confirmed by the absorption spectra of polarized light. An approximately 2-fold increase in the internal quantum yield (IQY) was observed for the G-PSI-attached electrode under 680 nm irradiation compared with that of the N-PSI-modified electrode. In addition, a 4-fold enhancement of the IQY was detected for cytochrome c (Cyt c) stacking on the G-PSI because of the electrostatic interaction, suggesting that Cyt c successfully secured the electron-transfer pathway.

Minding the Gap between Plant and Bacterial Photosynthesis within a Self-Assembling Biohybrid Photosystem

Many strategies for meeting mankind's future energy demands through the exploitation of plentiful solar energy have been influenced by the efficient and sustainable processes of natural photosynthesis. A limitation affecting solar energy conversion based on photosynthetic proteins is the selective spectral coverage that is the consequence of their particular natural pigmentation. Here we demonstrate the bottom-up formation of semisynthetic, polychromatic photosystems in mixtures of the chlorophyll-based LHCII major light harvesting complex from the oxygenic green plant Arabidopsis thaliana, the bacteriochlorophyll-based photochemical reaction center (RC) from the anoxygenic purple bacterium Rhodobacter sphaeroides and synthetic quantum dots (QDs). Polyhistidine tag adaptation of LHCII and the RC enabled predictable self-assembly of LHCII/RC/QD nanoconjugates, the thermodynamics of which could be accurately modeled and parametrized. The tricomponent biohybrid photosystems displayed enhanced solar energy conversion via either direct chlorophyll-to-bacteriochlorophyll energy transfer or an indirect pathway enabled by the QD, with an overall energy transfer efficiency comparable to that seen in natural photosystems.

Polychromatic solar energy conversion in pigment-protein chimeras that unite the two kingdoms of (bacterio)chlorophyll-based photosynthesis

Natural photosynthesis can be divided between the chlorophyll-containing plants, algae and cyanobacteria that make up the oxygenic phototrophs and a diversity of bacteriochlorophyll-containing bacteria that make up the anoxygenic phototrophs. Photosynthetic light harvesting and reaction centre proteins from both kingdoms have been exploited for solar energy conversion, solar fuel synthesis and sensing technologies, but the energy harvesting abilities of these devices are limited by each protein's individual palette of pigments. In this work we demonstrate a range of genetically-encoded, self-assembling photosystems in which recombinant plant light harvesting complexes are covalently locked with reaction centres from a purple photosynthetic bacterium, producing macromolecular chimeras that display mechanisms of polychromatic solar energy harvesting and conversion. Our findings illustrate the power of a synthetic biology approach in which bottom-up construction of photosystems using naturally diverse but mechanistically complementary components can be achieved in a predictable fashion through the encoding of adaptable, plug-and-play covalent interfaces.

The emerging science of electrosynbionics

Dramatic changes in electricity generation, use and storage are needed to keep pace with increasing demand while reducing carbon dioxide emissions. There is great potential for application of bioengineering in this area. We have the tools to re-engineer biological molecules and systems, and a significant amount of research and development is being carried out on technologies such as biophotovoltaics, biocapacitors, biofuel cells and biobatteries. However, there does not seem to be a satisfactory overarching term to describe this area, and I propose a new word-'electrosynbionics'. This is to be defined as: the creation of engineered devices that use components derived from or inspired by biology to perform a useful electrical function. Here, the phrase 'electrical function' is taken to mean the generation, use and storage of electricity, where the primary charge carriers may be either electrons or ions. 'Electrosynbionics' is distinct from 'bioelectronics', which normally relates to applications in sensing, computing or electroceuticals. Electrosynbionic devices have the potential to solve challenges in electricity generation, use and storage by exploiting or mimicking some of the desirable attributes of biological systems, including high efficiency, benign operating conditions and intricate molecular structures.

Engineered photoproteins that give rise to photosynthetically-incompetent bacteria are effective as photovoltaic materials for biohybrid photoelectrochemical cells

Reaction centre/light harvesting proteins such as the RCLH1X complex from Rhodobacter sphaeroides carry out highly quantum-efficient conversion of solar energy through ultrafast energy transfer and charge separation, and these pigment-proteins have been incorporated into biohybrid photoelectrochemical cells for a variety of applications. In this work we demonstrate that, despite not being able to support normal photosynthetic growth of Rhodobacter sphaeroides, an engineered variant of this RCLH1X complex lacking the PufX protein and with an enlarged light harvesting antenna is unimpaired in its capacity for photocurrent generation in two types of bio-photoelectrochemical cells. Removal of PufX also did not impair the ability of the RCLH1 complex to act as an acceptor of energy from synthetic light harvesting quantum dots. Unexpectedly, the removal of PufX led to a marked improvement in the overall stability of the RCLH1 complex under heat stress. We conclude that PufX-deficient RCLH1 complexes are fully functional in solar energy conversion in a device setting and that their enhanced structural stability could make them a preferred choice over their native PufX-containing counterpart. Our findings on the competence of RCLH1 complexes for light energy conversion in vitro are discussed with reference to the reason why these PufX-deficient proteins are not capable of light energy conversion in vivo.

Long-term protein packaging in bio-ionic liquids: Improved catalytic activity and enhanced stability of cytochrome C against multiple stresses

There is a considerable interest in the use of structurally stable and catalytically active enzymes, such as cytochrome C (Cyt C), in the pharmaceutical and fine chemical industries. However, harsh process conditions, such as temperature, pH, and presence of organic solvents, are the major barriers to the effective use of enzymes in biocatalysis. Herein, we demonstrate the suitability of bio-based ionic liquids (ILs) formed by the cholinium cation and dicarboxylate-based anions as potential media for enzymes, in which remarkable enhanced activity and improved stability of Cyt C against multiple stresses were obtained. Among the several bio-ILs studied, an exceptionally high catalytic activity (> 50-fold) of Cyt C was observed in aqueous solutions of cholinium glutarate ([Ch][Glu]; 1g/mL) as compared to the commonly used phosphate buffer solutions (pH 7.2), and > 25-fold as compared to aqueous solutions of cholinium dihydrogen phosphate ([Ch][Dhp]; 0.5g/mL) -the best known IL for long term stability of Cyt C. The catalytic activity of the enzyme in presence of bio-ILs was retained against several external stimulus, such as chemical denaturants (H2O2 and GuHCl), and temperatures up to 120 °C. The observed enzyme activity is in agreement with its structural stability, as confirmed by UV-Vis, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectroscopies. Taking advantage of the multi-ionization states of di/tri-carboxylic acids, the pH was switched from acidic to basic by the addition of the corresponding carboxylic acid and choline hydroxide, respectively. The activity was found to be maximum at a 1:1 ratio of [Ch][carboxylate], with a pH in the range from 3 to 5.5. Moreover, it was found that the bio-ILs studied herein protect the enzyme against protease digestion and allow long-term storage (at least for 21 weeks) at room temperature. An attempt by molecular docking was also made to better understand the efficacy of the investigated bio-ILs towards the enhanced activity and long term stability of Cyt C. The results showed that dicarboxylates anions interact with the active site's amino acids of the enzyme through H-bonding and electrostatic interactions, which are responsible for the observed enhancement of the catalytic activity. Finally, it is demonstrated that Cyt C can be successfully recovered from the aqueous solution of bio-ILs and reused without compromising its yield, structural integrity and catalytic activity, thereby overcoming the major limitations in the use of IL-protein systems in biocatalysis.