Artificial Cellulosome Complex from the Self-Assembly of Ni-NTA-Functionalized Polymeric Micelles and Cellulases

Combinatorial optimization of the hybrid cellulase complex structure designed from modular libraries

Cellulase selectively recognizes cellulose surfaces and cleaves their β-1,4-glycosidic bonds. Combining hydrolysis using cellulase and fermentation can produce alternative fuels and chemical products. However, anaerobic bacteria produce only low levels of highly active cellulase complexes so-called cellulosomes. Therefore, we designed hybrid cellulase complexes from 49 biotinylated catalytic domain (CD) and 30 biotinylated cellulose-binding domain (CBD) libraries on streptavidin-conjugated nanoparticles to enhance cellulose hydrolysis by mimicking the cellulosome structure. The hybrid cellulase complex, incorporating both native CD and CBD, significantly improved reducing sugar production from cellulose compared to free native modular enzymes. The optimal CBD for each hybrid cellulase complex differed from that of the native enzyme. The most effective hybrid cellulase complex was observed with the combination of CD6-4 from Thermobifida fusca YX and CBD46 from the Bacillus halodurans C-125. The hybrid cellulase complex/CD6-4-CBD46 and -CD6-4-CBD2-5 combinations showed increased reducing sugar production. Similar results were also observed in microcrystalline cellulose degradation. Furthermore, clustering on nanoparticles enhanced enzyme thermostability. Our results demonstrate that hybrid cellulase complex structures improve enzyme function through synergistic effects and extend the lifespan of the enzyme.

Cellulase immobilization to enhance enzymatic hydrolysis of lignocellulosic biomass: An all-inclusive review

Cellulase-mediated lignocellulosic biorefinery plays a crucial role in the production of high-value biofuels and chemicals, with enzymatic hydrolysis being an essential component. The advent of cellulase immobilization has revolutionized this process, significantly enhancing the efficiency, stability, and reusability of cellulase enzymes. This review offers a thorough analysis of the fundamental principles underlying immobilization, encompassing various immobilization approaches such as physical adsorption, covalent binding, entrapment, and cross-linking. Furthermore, it explores a diverse range of carrier materials, including inorganic, organic, and hybrid/composite materials. The review also focuses on emerging approaches like multi-enzyme co-immobilization, oriented immobilization, immobilized enzyme microreactors, and enzyme engineering for immobilization. Additionally, it delves into novel carrier technologies like 3D printing carriers, stimuli-responsive carriers, artificial cellulosomes, and biomimetic carriers. Moreover, the review addresses recent obstacles in cellulase immobilization, including molecular-level immobilization mechanism, diffusion limitations, loss of cellulase activity, cellulase leaching, and considerations of cost-effectiveness and scalability. The knowledge derived from this review is anticipated to catalyze the evolution of more efficient and sustainable biocatalytic systems for lignocellulosic biomass conversion, representing the current state-of-the-art in cellulase immobilization techniques.

Three-dimensional (3D) bioprinting of medium toughened dipeptide hydrogel scaffolds with Hofmeister effect

Short peptide self-assembled hydrogels as 3D bioprinting inks show excellent biocompatibility and diverse functional expansion, and have broad application prospects in cell culture and tissue engineering. However, the preparation of biological hydrogel inks with adjustable mechanical strength and controllable degradation for 3D bioprinting still faces big challenges. Herein, we develop dipeptide bio-inks that can be gelled in-situ based on Hofmeister sequence, and prepare hydrogel scaffold by using a layer-by-layer 3D printing strategy. Excitingly, after the introduction of Dulbecco's Modified Eagle's medium (DMEM), which is necessary for cell culture, the hydrogel scaffolds show an excellent toughening effect, which matches the needs of cell culture. It's notable that in the whole process of preparation and 3D printing of hydrogel scaffolds, no cross-linking agent, ultraviolet (UV), heating or other exogenous factors are involved, ensuring high biosafety and biocompatibility. After two weeks of 3D culture, millimeter-sized cell spheres are obtained. This work provides an opportunity for the development of short peptide hydrogel bioinks without exogenous factors in 3D printing, tissue engineering, tumor simulant reconstruction and other biomedical fields.

Improvement of Cellulomonas fimi endoglucanase CenA by multienzymatic display on a decameric structural scaffold

The development of multifunctional particles using polymeric scaffolds is an emerging technology for many nanobiotechnological applications. Here we present a system for the production of multifunctional complexes, based on the high affinity non-covalent interaction of cohesin and dockerin modules complementary fused to decameric Brucella abortus lumazine synthase (BLS) subunits, and selected target proteins, respectively. The cohesin-BLS scaffold was solubly expressed in high yield in Escherichia coli, and revealed a high thermostability. The production of multienzymatic particles using this system was evaluated using the catalytic domain of Cellulomonas fimi endoglucanase CenA recombinantly fused to a dockerin module. Coupling of the enzyme to the scaffold was highly efficient and occurred with the expected stoichiometry. The decavalent enzymatic complexes obtained showed higher cellulolytic activity and association to the substrate compared to equivalent amounts of the free enzyme. This phenomenon was dependent on the multiplicity and proximity of the enzymes coupled to the scaffold, and was attributed to an avidity effect in the polyvalent enzyme interaction with the substrate. Our results highlight the usefulness of the scaffold presented in this work for the development of multifunctional particles, and the improvement of lignocellulose degradation among other applications. KEY POINTS: • New system for multifunctional particle production using the BLS scaffold • Higher cellulolytic activity of polyvalent endoglucanase compared to the free enzyme • Amount of enzyme associated to cellulose is higher for the polyvalent endoglucanase.

Effect of multimodularity and spatial organization of glycoside hydrolases on catalysis

The wide diversity among the carbohydrate-active enzymes (CAZymes) reflects the equally broad versatility in terms of composition and chemicals bonds found in the plant cell wall polymers on which they are active. This diversity is also expressed through the various strategies developed to circumvent the recalcitrance of these substrates to biological degradation. Glycoside hydrolases (GHs) are the most abundant of the CAZymes and are expressed as isolated catalytic modules or in association with carbohydrate-binding module (CBM), acting in synergism within complex arrays of enzymes. This multimodularity can be even more complex. The cellulosome presents a scaffold protein immobilized to the outer membrane of some microorganisms on which enzymes are grafted to prevent their dispersion and increase catalytic synergism. In polysaccharide utilization loci (PUL), GHs are also distributed across the membranes of some bacteria to co-ordinate the deconstruction of polysaccharides and the internalization of metabolizable carbohydrates. Although the study and characterization of these enzymatic activities need to take into account the entirety of this complex organization-in particular because of the dynamics involved in it-technical problems limit the present study to isolated enzymes. However, these enzymatic complexes also have a spatiotemporal organization, whose still neglected aspect must be considered. In the present review, the different levels of multimodularity that can occur in GHs will be reviewed, from its simplest forms to the most complex. In addition, attempts to characterize or study the effect on catalytic activity of the spatial organization within GHs will be addressed.

Advances in consolidated bioprocessing using synthetic cellulosomes

The primary obstacle impeding the more widespread use of biomass for energy and chemical production is the absence of a low-cost technology for overcoming their recalcitrant nature. It has been shown that the overall cost can be reduced by using a 'consolidated' bioprocessing (CBP) approach, in which enzyme production, biomass hydrolysis, and sugar fermentation can be combined. Cellulosomes are enzyme complexes found in many anaerobic microorganisms that are highly efficient for biomass depolymerization. While initial efforts to display synthetic cellulosomes have been successful, the overall conversion is still low for practical use. This limitation has been partially alleviated by displaying more complex cellulsome structures either via adaptive assembly or by using synthetic consortia. Since synthetic cellulosome nanostructures have also been created using either protein nanoparticles or DNA as a scaffold, there is the potential to tether these nanostructures onto living cells in order to further enhance the overall efficiency.

Cellulase Immobilization on Nanostructured Supports for Biomass Waste Processing

Nanobiocatalysts, i.e., enzymes immobilized on nanostructured supports, received considerable attention because they are potential remedies to overcome shortcomings of traditional biocatalysts, such as low efficiency of mass transfer, instability during catalytic reactions, and possible deactivation. In this short review, we will analyze major aspects of immobilization of cellulase-an enzyme for cellulosic biomass waste processing-on nanostructured supports. Such supports provide high surface areas, increased enzyme loading, and a beneficial environment to enhance cellulase performance and its stability, leading to nanobiocatalysts for obtaining biofuels and value-added chemicals. Here, we will discuss such nanostructured supports as carbon nanotubes, polymer nanoparticles (NPs), nanohydrogels, nanofibers, silica NPs, hierarchical porous materials, magnetic NPs and their nanohybrids, based on publications of the last five years. The use of magnetic NPs is especially favorable due to easy separation and the nanobiocatalyst recovery for a repeated use. This review will discuss methods for cellulase immobilization, morphology of nanostructured supports, multienzyme systems as well as factors influencing the enzyme activity to achieve the highest conversion of cellulosic biowaste into fermentable sugars. We believe this review will allow for an enhanced understanding of such nanobiocatalysts and processes, allowing for the best solutions to major problems of sustainable biorefinery.

Cellulose-deconstruction potential of nano-biocatalytic systems: A strategic drive from designing to sustainable applications of immobilized cellulases

Nanostructured materials along with an added value of polymers-based support carriers have gained high interest and considered ideal for enzyme immobilization. The recently emerged nanoscience interface in the form of nanostructured materials combined with immobilized-enzyme-based bio-catalysis has now become research and development frontiers in advance and applied bio-catalysis engineering. With the involvement of nanoscience, various polymers have been thoroughly developed and exploited to nanostructured engineer constructs as ideal support carriers/matrices. Such nanotechnologically engineered support carriers/matrix possesses unique structural, physicochemical, and functional attributes which equilibrate principal factors and strengthen the biocatalysts efficacy for multipurpose applications. In addition, nano-supported catalysts are potential alternatives that can outstrip several limitations of conventional biocatalysts, such as reduced catalytic efficacy and turnover, low mass transfer efficiency, instability during the reaction, and most importantly, partial, or complete inhibition/deactivation. In this context, engineering robust and highly efficient biocatalysts is an industrially relevant prerequisite. This review comprehensively covered various biopolymers and nanostructured materials, including silica, hybrid nanoflower, nanotubes or nanofibers, nanomembranes, graphene oxide nanoparticles, metal-oxide frameworks, and magnetic nanoparticles as robust matrices for cellulase immobilization. The work is further enriched by spotlighting applied and industrially relevant considerations of nano-immobilized cellulases. For instance, owing to the cellulose-deconstruction features of nano-immobilized cellulases, the applications like lignocellulosic biomass conversion into industrially useful products or biofuels, improved paper sheet density and pulp beat in paper and pulp industry, fruit juice clarification in food industry are evident examples of cellulases, thereof are discussed in this work.

Orthogonal Enzymatic Conjugation Reactions Create Chitin Binding Domain Grafted Chitinase Polymers with Enhanced Antifungal Activity

Enzymatic reaction offers site-specific conjugation of protein units to form protein conjugates or protein polymers with intrinsic functions. Herein, we report horseradish peroxidase (HRP)- and microbial transglutaminase (MTG)-catalyzed orthogonal conjugation reactions to create antifungal protein polymers composed of Pteris ryukyuensis chitinase-A (ChiA) and its two domains, catalytic domain, CatD, and chitin-binding domain, LysM₂. We engineered the ChiA and CatD by introducing a peptide tag containing tyrosine (Y-tag) at N-termini and a peptide tag containing lysine and tyrosine (KY-tag) at C-termini to construct Y-ChiA-KY and Y-CatD-KY. Also, LysM₂ with Y-tag and KY-tag (Y-LysM₂-KY) or with a glutamine-containing peptide tag (Q-tag) (LysM₂-Q) were constructed. The proteins with Y-tag and KY-tag were efficiently polymerized by HRP reaction through the formation of dityrosine bonds at the tyrosine residues in the peptide tags. The Y-CatD-KY polymer was further treated by MTG to orthogonally graft LysM₂-Q to the KY-tag via isopeptide formation between the side chains of the glutamine and lysine residues in the peptide tags to form LysM₂-grafted CatD polymer. The LysM₂-grafted CatD polymer exhibited significantly higher antifungal activity than the homopolymer of Y-ChiA-KY and the random copolymer of Y-CatD-KY and Y-LysM₂-KY, demonstrating that the structural differences of artificial chitinase polymers have a significant impact on the antifungal activity. This strategy of polymerization and grafting reaction of protein can contribute to the further research and development of functional protein polymers for specific applications in various fields in biotechnology.

Enzymatic characteristics of immobilized carbonic anhydrase and its applications in CO2 conversion

Native carbonic anhydrase (CA) has been widely used in several different applications due to its catalytic function in the interconversion of carbon dioxide (CO₂) and carbonic acid. However, subject to its stability and recyclability, native CA often deactivates when in harsh environments, which restricts its applications in the commercial market. Maintaining the stability and high catalytic activity of CA is challenging. Immobilization provides an effective route that can improve enzymatic stability. Through the interaction of covalent bonds and van der Waals forces, water-soluble CA can be combined with various insoluble supports to form water-insoluble immobilized CA so that CA stability and utilization can be greatly improved. However, if the immobilization method or immobilization condition is not suitable, it often leads to a decrease in CA activity, reducing the application effects on CO₂ conversion. In this review, we discuss existing immobilization methods and applications of immobilized CA in the environmental field, such as the mineralization of carbon dioxide and multienzyme cascade catalysis based on CA. Additionally, prospects in current development are outlined. Because of the many outstanding and superior properties after immobilization, CA is likely to be used in a wide variety of scientific and technical areas in the future.

Glucan Conversion and Membrane Recovery of Biomimetic Cellulosomes During Lignocellulosic Biomass Hydrolysis

Enzyme immobilization has been identified as one way to recycle enzymes and reduce processing costs during enzymatic hydrolysis of lignocellulosic materials. However, most immobilization methods have not been attractive to lignocellulosic processing plants. In this study, cellulase enzymes were attached to a copolymer of glycidyl methacrylate (GMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) to make polymer-enzyme conjugates (PECs) and facilitate recovery using a 50-kDa molecular weight cutoff membrane. Glucan conversion during biomass hydrolysis was investigated using new PECs and PECs recovered after an initial hydrolysis stage. Enzyme immobilization on PECs did not reduce effectiveness during the initial hydrolysis. Temperature and pH showed similar effects on free enzymes and PECs. PECs facilitated higher conversion rates than free enzymes at high biomass loadings. Recovered PECs were used to achieve approximately 100% glucan conversion in a subsequent hydrolysis step when supplemented with 40% of the free enzyme used in the first stage. The combination of PECs and membrane recovery has the potential to reduce hydrolysis cost during cellulosic bioprocessing.

A two-step method for the synthesis of magnetic immobilized cellulase with outstanding thermal stability and reusability

The cellulase electrostatically adsorbed on the surface of Fe₃O₄@C magnetic nanoparticles was embedded with silica to form the immobilized cellulase. The stability and reusability were greatly improved, while the synthesis process was simple.

Enhanced P450 fatty acid decarboxylase catalysis by glucose oxidase coupling and co-assembly for biofuel generation

Cytochrome P450 OleT is a fatty acid decarboxylase that uses hydrogen peroxide (H₂O₂) to catalyze the production of terminal alkenes, which are industrially important chemicals with biofuel and synthetic applications. Despite its requirement for large turnover levels, high concentrations of H₂O₂ may cause heme group degradation, diminishing enzymatic activity and limiting broad application for synthesis. Here, we report an artificial enzyme cascade composed of glucose oxidase (GOx) and OleT_SA from Staphylococcus aureus for efficient terminal alkene production. By adjusting the ratio of GOx to OleT_SA, the GOx-based tandem catalysis shows significantly improved product yield compared to the H₂O₂ injection method. Moreover, the co-assembly of the GOx/OleT_SA enzymes with a polymer, forming polymer-dual enzymes nanoparticles, displays improved activity compared to the free enzyme. This dual strategy provides a simple and efficient system to transform a naturally abundant feedstock to industrially important chemicals.

Progress in Ameliorating Beneficial Characteristics of Microbial Cellulases by Genetic Engineering Approaches for Cellulose Saccharification

Lignocellulosic biomass is a renewable and sustainable energy source. Cellulases are the enzymes that cleave β-1, 4-glycosidic linkages in cellulose to liberate sugars that can be fermented to ethanol, butanol, and other products. Low enzyme activity and yield, and thermostability are, however, some of the limitations posing hurdles in saccharification of lignocellulosic residues. Recent advancements in synthetic and systems biology have generated immense interest in metabolic and genetic engineering that has led to the development of sustainable technology for saccharification of lignocellulosics in the last couple of decades. There have been several attempts in applying genetic engineering in the production of a repertoire of cellulases at a low cost with a high biomass saccharification. A diverse range of cellulases are produced by different microbes, some of which are being engineered to evolve robust cellulases. This review summarizes various successful genetic engineering strategies employed for improving cellulase kinetics and cellulolytic efficiency.