Mesoporous phenylalanine ammonia lyase microspheres with improved stability through calcium carbonate templating

Recent trends in targeted delivery of smart nanocarrier-based microbial enzymes for therapeutic applications

Smart carrier-based immobilization has widened the use of enzymes for the treatment of several disorders. Large surface areas, tunable morphology, and surface modification ability aid the targeted and controlled release of therapeutic enzymes from such formulations. Smart nanocarriers, such as polymeric carriers, liposomes, and silica have also increased the stability, half-life, and permeability of these enzymes. In this review, summarize recent advances in the smart immobilization of microbial enzymes and their development as precision nanomedicine for the treatment of cancer, thrombosis, phenylketonuria (PKU), and wound healing. We also discuss the challenges and measures to be adopted for the successful clinical translation of these formulations.

Tandem-biocatalysis reactors constructed by topological evolution of CaCO3 particles into hollow metal hydroxide spheres

Despite remarkable advances in the design and synthesis of hollow inorganic spheres (HISs), the harsh synthetic conditions have precluded the applications of HISs to biochemical and biological fields. Herein we report a biocompatible strategy for synthesizing metal hydroxide HISs (MH-HISs) by simply mixing CaCO3 particles with metal ions in water. The ion-exchange reaction between Ca2+ and metal ions leads to the structural and chemical evolution from solid CaCO3 particles to hollow MH-HISs via core-shell and yolk-shell structures, while enabling the encapsulation of enzymes to the shells without loss of catalytic activities. The biocompatible protocol makes multienzymatic cascade reactions achievable, with great recyclability due to mechanical durability of MH-HISs.

Immobilization of BoPAL3 Phenylalanine Ammonia-Lyase on Electrospun Nanofibrous Membranes of Polyvinyl Alcohol/Nylon 6/Chitosan Crosslinked with Dextran Polyaldehyde

Phenylalanine ammonia-lyase (PAL, EC 4.3.1.24) is common in plants and catalyzes the formation of trans-cinnamic acid and ammonia via phenylalanine deamination. Recombinant Bambusa oldhamii BoPAL3 protein expressed in Escherichia coli was immobilized on an electrospun nanofibrous membrane using dextran polyaldehyde as a crosslinker. The immobilized BoPAL3 protein exhibited comparable kinetic properties with the free BoPAL3 protein and could be recycled for six consecutive cycles compared with the free BoPAL3 protein. The residual activity of the immobilized BoPAL3 protein was 84% after 30 days of storage at 4 °C, whereas the free BoPAL3 protein retained 56% residual activity in the same storage conditions. Furthermore, the resistance of the immobilized BoPAL3 protein to chemical denaturants was greatly increased. Therefore, the BoPAL3 protein can be immobilized using the natural dextran polyaldehyde crosslinker in place of the conventional chemical crosslinker. Nanofibrous membranes made from polyvinyl alcohol (PVA), nylon 6, and chitosan (CS) are incredibly stable and useful for future industrial applications.

Preparation of combined cross-linked enzyme aggregates containing galactitol dehydrogenase and NADH oxidase for L-tagatose synthesis via in situ cofactor regeneration

The combined cross-linked enzyme aggregates (combi-CLEAs) containing galactitol dehydrogenase (Gdh) and NADH oxidase (Nox) were prepared for L-tagatose synthesis. To prevent the excess consumption of cofactor, Nox in the combi-CLEAs was used to in situ regenerate NAD⁺. In the immobilization process, ammonia sulfate and glutaraldehyde were used as the precipitant and cross-linking reagent, respectively. The preparation conditions were optimized as follows: 60% ammonium sulfate, 1:1 (molar ratio) of Gdh to Nox, 20:1 (molar ratio) of protein to glutaraldehyde, and 6 h of cross-linking time at 35 °C. Under these conditions, the activity of the combi-CLEAs was 210 U g^-1. The combi-CLEAs exhibited higher thermostability and preserved 51.5% of the original activity after eight cycles of reuses at 45 °C. The combi-CLEAs were utilized for the preparation of L-tagatose without by-products. Therefore, the combi-CLEAs have the industrial potential for the bioconversion of galactitol to L-tagatose.

Phenylalanine, Tyrosine, and DOPA Are bona fide Substrates for Bambusa oldhamii BoPAL4

Phenylalanine ammonia-lyase (PAL) links the plant primary and secondary metabolisms, and its product, trans-cinnamic acid, is derived into thousands of diverse phenylpropanoids. Bambusa oldhamii BoPAL4 has broad substrate specificity using L-phenylalanine, L-tyrosine, and L-3,4-dihydroxy phenylalanine (L-DOPA) as substrates to yield trans-cinnamic acid, p-coumaric acid, and caffeic acid, respectively. The optimum reaction pH of BoPAL4 for three substrates was measured at 9.0, 8.5, and 9.0, respectively. The optimum reaction temperatures of BoPAL4 for three substrates were obtained at 50, 60, and 40 °C, respectively. The Km values of BoPAL4 for three substrates were 2084, 98, and 956 μM, respectively. The kcat values of BoPAL4 for three substrates were 1.44, 0.18, and 0.06 σ−1, respectively. The major substrate specificity site mutant, BoPAL4-H123F, showed better affinity toward L-phenylalanine by decreasing its Km value to 640 μM and increasing its kcat value to 1.87 s−1. In comparison to wild-type BoPAL4, the specific activities of BoPAL4-H123F using L-tyrosine and L-DOPA as substrates retained 5.4% and 17.8% residual activities. Therefore, L-phenylalanine, L-tyrosine, and L-DOPA are bona fide substrates for BoPAL4.

Production of Trans-Cinnamic Acid by Immobilization of the Bambusa oldhamii BoPAL1 and BoPAL2 Phenylalanine Ammonia-Lyases on Electrospun Nanofibers

Phenylalanine ammonia-lyase (PAL) catalyzes the nonoxidative deamination of phenylalanine to yield trans-cinnamic acid and ammonia. Recombinant Bambusa oldhamii BoPAL1/2 proteins were immobilized onto electrospun nanofibers by dextran polyaldehyde as a cross-linking agent. A central composite design (CCD)-response surface methodology (RSM) was utilized to optimize the electrospinning parameters. Escherichia coli expressed eBoPAL2 exhibited the highest catalytic efficiency among four enzymes. The optimum conditions for fabricating nanofibers were determined as follows: flow rate of 0.10 mL/h, voltage of 13.8 kV, and distance of 13 cm. The response surface models were used to obtain the smaller the fiber diameters as well as the highest PAL activity in the enzyme immobilization. Compared with free BoPALs, immobilized BoPALs can be reused for at least 6 consecutive cycles. The remained activity of the immobilized BoPAL proteins after storage at 4 °C for 30 days were between 75 and 83%. In addition, the tolerance against denaturants of the immobilized BoPAL proteins were significantly enhanced. As a result, the dextran polyaldehyde natural cross-linking agent can effectively replace traditional chemical cross-linking agents for the immobilization of the BoPAL enzymes. The PAL/nylon 6/polyvinyl alcohol (PVA)/chitosan (CS) nanofibers made are extremely stable and are practical for industrial applications in the future.

Current Status and Future Perspectives of Supports and Protocols for Enzyme Immobilization

The market for industrial enzymes has witnessed constant growth, which is currently around 7% a year, projected to reach $10.5 billion in 2024. Lipases are hydrolase enzymes naturally responsible for triglyceride hydrolysis. They are the most expansively used industrial biocatalysts, with wide application in a broad range of industries. However, these biocatalytic processes are usually limited by the low stability of the enzyme, the half-life time, and the processes required to solve these problems are complex and lack application feasibility at the industrial scale. Emerging technologies create new materials for enzyme carriers and sophisticate the well-known immobilization principles to produce more robust, eco-friendlier, and cheaper biocatalysts. Therefore, this review discusses the trending studies and industrial applications of the materials and protocols for lipase immobilization, analyzing their advantages and disadvantages. Finally, it summarizes the current challenges and potential alternatives for lipases at the industrial level.

Biopolymer-Based Multilayer Capsules and Beads Made via Templating: Advantages, Hurdles and Perspectives

One of the undeniable trends in modern bioengineering and nanotechnology is the use of various biomolecules, primarily of a polymeric nature, for the design and formulation of novel functional materials for controlled and targeted drug delivery, bioimaging and theranostics, tissue engineering, and other bioapplications. Biocompatibility, biodegradability, the possibility of replicating natural cellular microenvironments, and the minimal toxicity typical of biogenic polymers are features that have secured a growing interest in them as the building blocks for biomaterials of the fourth generation. Many recent studies showed the promise of the hard-templating approach for the fabrication of nano- and microparticles utilizing biopolymers. This review covers these studies, bringing together up-to-date knowledge on biopolymer-based multilayer capsules and beads, critically assessing the progress made in this field of research, and outlining the current challenges and perspectives of these architectures. According to the classification of the templates, the review sequentially considers biopolymer structures templated on non-porous particles, porous particles, and crystal drugs. Opportunities for the functionalization of biopolymer-based capsules to tailor them toward specific bioapplications is highlighted in a separate section.

Codon-Optimized Rhodotorula glutinis PAL Expressed in Escherichia coli With Enhanced Activities

PAL (phenylalanine ammonia lyase) is important for secondary metabolite production in plants and microorganisms. There is broad interest in engineering PAL for its biocatalytic applications in industry, agriculture, and medicine. The production of quantities of high-activity enzymes has been explored by gene cloning and heterogeneous expression of the corresponding protein. Here, we cloned the cDNA of Rhodotorula glutinis PAL (RgPAL) and introduced codon optimization to improve protein expression in Escherichia coli and enzyme activities in vitro. The RgPAL gene was cloned by reverse transcription and named pal-wt. It had a full-length of 2,121 bp and encoded a 706-amino-acid protein. The pal-wt was inefficiently expressed in E. coli, even when the expression host and physical conditions were optimized. Therefore, codon optimization was used to obtain the corresponding gene sequence, named pal-opt, in order to encode the same amino acid for the RgPAL protein. The recombinant protein encoded by pal-opt, named PAL-opt, was successfully expressed in E. coli and then purified to detect its enzymatic activity in vitro. Consequently, 55.33 ± 0.88 mg/L of PAL-opt protein with a specific activity of 1,219 ± 147 U/mg and K_m value of 609 μM for substrate L-phenylalanine was easily obtained. The enzyme protein also displayed tyrosine ammonia lyase (TAL)–specific activity of 80 ± 2 U/mg and K_m value of 13.3 μM for substrate L-tyrosine. The bifunctional enzyme RgPAL/TAL (PAL-opt) and its easy expression advantage will provide an important basis for further applications.

Paper-based biosensor based on phenylalnine ammonia lyase hybrid nanoflowers for urinary phenylalanine measurement

The Phenylketonuria (PKU) is an inborn defect of phenylalanine (Phe) metabolism, in which Phe accumulated in the blood causing alterations at the central nervous system. Therefore, the detection of PKU is very important for the early diagnosis of PKU patients. However, existing tests for PKU are time-consuming and require high-resource laboratories. In this study, a novel paper-based biosensor based on phenylalnine ammonia lyase (PAL) hybrid nanoflowers was constructed that provides a semi-quantitative output of the concentration of Phe from urine samples. PAL@Ca₃(PO₄)₂ hybrid nanoflowers (PAL@NF) were first prepared using PAL and Ca²⁺. Synthesis conditions of the PAL@NF on the formation of the PAL@NF were optimized. The PAL@NF exhibited 90% activity recovery under optimal condition. Compared with free PAL, the PAL@NF displayed good storage stability and increased tolerance to proteolysis. After five consecutive operating cycles, the PAL@NF still retained 73% of its initial activity, indicating excellent reusability. Furthermore, the paper-based biosensor was able to detect Phe concentration in urine samples, and exhibited good linearity to the Phe concentrations in the range from 60 to 2400 μM and the response time was only about 10 min. Therefore, the paper-based biosensor can be a promising candidate as a biosensor for the detection of PKU.

Biomedical applications of microbial phenylalanine ammonia lyase: Current status and future prospects

Phenylalanine ammonia lyase (PAL) has recently emerged as an important therapeutic enzyme with several biomedical applications. The enzyme catabolizes l-phenylalanine to trans-cinnamate and ammonia. PAL is widely distributed in higher plants, some algae, ferns, and microorganisms, but absent in animals. Although microbial PAL has been extensively exploited in the past for producing industrially important metabolites, its high substrate specificity and catalytic efficacy lately spurred interest in its biomedical applications. PEG-PAL drug named Palynziq™, isolated from Anabaena variabilis has been recently approved for the treatment of adult phenylketonuria (PKU) patients. Further, it has exhibited high potency in regressing tumors and treating tyrosine related metabolic abnormalities like tyrosinemia. Several therapeutically valuable metabolites have been biosynthesized via its catalytic action including dietary supplements, antimicrobial peptides, aspartame, amino-acids, and their derivatives. This review focuses on all the prospective biomedical applications of PAL. It also provides an overview of the structure, production parameters, and various strategies to improve the therapeutic potential of this enzyme. Engineered PAL with improved pharmacodynamic and pharmacokinetic properties will further establish this enzyme as a highly efficient biological drug.

Carrier-Free Immobilization of Rutin Degrading Enzyme Extracted From Fusarium spp

In this study, a strain with rutin degrading enzyme (RDE) activity was screened from moldy tartary buckwheat and subsequently identified as Fusarium spp. The structure and enzyme characteristics of CLEA-RDE formed by immobilization via cross-linking were then investigated. Further, the optimal catalysis conditions of CLEA-RDE in natural deep eutectic solvents (NADESs) serving as hydrolysis solvents were also investigated. The results of SEM and spectrum indicated that CLEA-RDE became more stable than free-RDE due to the cross-linking. Interestingly, CLEA-RDE showed a wider range of pH adaptation and higher tolerance to low temperatures (20 – 30°C) and hydrophobic environments. The results of orthogonal experiments revealed that the optimal condition for rutin hydrolysis was under pH 5.0 and 40^oC with the degradation rate of 10.65 mg min⁻¹ L⁻¹. The preparation of CLEA-RDE without a carrier-based immobilization method reduces the loss of enzyme activity, improves the stability of the enzyme and can be applied to the investigation of immobilization of various enzymes, thus providing a referred idea for the improvement of catalysts in industrial production.

Cross-linked enzyme aggregates of arylamidase from Cupriavidus oxalaticus ICTDB921: process optimization, characterization, and application for mitigation of acrylamide in industrial wastewater

Acrylamidase produced by Cupriavidus oxalaticus ICTDB921 was recovered directly from the fermentation broth by ammonium sulfate (40-50%) precipitation and then stabilized by cross-linking with glutaraldehyde. The optimum conditions for the preparation of cross-linked enzyme aggregates of acrylamidase (acrylamidase-CLEAs) were using 60 mM glutaraldehyde for 10 min at 35 °C and initial broth pH of 7.0. Acrylamidase-CLEAs were characterized by SDS-PAGE, FTIR, particle size analyzer and SEM. Cross-linking shifted the optimal temperature and pH from 70 to 50 °C and 5-7 to 6-8, respectively. It also altered the secondary structure fractions, pH and thermal stability along with the kinetic constants, K_m and V_max, respectively. A complete degradation of acrylamide ~ 1.75 g/L in industrial wastewater was achieved after 60 min in a batch process under optimum operating conditions, and the kinetics was best represented by Edward model (R² = 0.70). Acrylamidase-CLEAs retained ~ 40% of its initial activity after three cycles for both pure acrylamide and industrial wastewater, and were stable for 15 days at 4 °C, retaining ~ 25% of its original activity.

Synthesis and properties of porous CLEAs lipase by the calcium carbonate template method and its application in biodiesel production

In this work, porous cross-linked enzyme aggregates (p-CLEAs) were synthesized by the in situ co-precipitation method using CaCO₃ microparticles as templates. The preparation procedure involved the immobilization of crude lipase as CLEAs via precipitation with ammonium sulfate and entrapping these lipase molecules into the CaCO₃ templates, followed by DTT (dithiothreitol)-induced assembly of lipase molecules to form lipase microparticles (lipase molecules were assembled into microparticles internally using disulfide bonds within the lipase molecules as the molecular linkers and stimulated by dithiothreitol); finally, the removal of CaCO₃ templates was performed by EDTA to form pores in CLEAs. The scanning electron microscopy analysis of p-CLEAs showed a porous structure. p-CLEAs showed obvious improvement in thermal stability (after incubation at 65 °C, p-CLEAs lipase retained 86% relative activity, while free lipase retained only 33.67%) and pH stability (p-CLEAs relative activity was over 90% while for free lipase, the relative activity ranged from 72% to 89% from pH 6 to 9) than free lipase and could hold relatively high activity retention without activity loss at 4 °C for more than six months. The application of p-CLEAs in producing biodiesel showed a higher degree of conversion. The conversion of fatty acid methyl ester (FAME) was 89.7%; this value was higher by approximately 7.4% compared to that of the conventional CLEAs under the optimized conditions of a methanol–oil molar ratio of 6 : 1, with a p-CLEAs lipase dose of 20% and water content of 3% at 45 °C for 24 h. The FAME conversion remained greater than 70% even after reusing the p-CLEAs lipase for 8 reactions. The results demonstrated that the p-CLEAs lipase is suitable for applications in the preparation of biodiesel.

Porous cross-linked enzyme aggregates (p-CLEAs) were synthesized. This p-CLEAs presented a complete structure with abundant channels, large specific surface and more efficient catalytic effect compared with conventional CLEAs.

The mechanism of catalase loading into porous vaterite CaCO3 crystals by co-synthesis

The mechanism of catalase loading into vaterite CaCO₃ crystals through co-synthesis is deciphered showing the crucial role of Ca²⁺-induced catalase aggregation.

Co-immobilization of glucose oxidase and catalase in silica inverse opals for glucose removal from commercial isomaltooligosaccharide

In this work, glucose oxidase (GOD) and catalase (CAT) were co-immobilized on novel silica inverse opals (IO-SiO₂) through sol-gel process. The immobilized bi-enzyme system named GOD/CAT@IO-SiO₂ was successfully fabricated and characterized. Morphology characterization indicated that GOD/CAT@IO-SiO₂ had hierarchical porous structure, and the pore diameter of macroporous and mesoporous were 500±50nm and 6.8nm, respectively. The macrospores were connected through windows of 100±30nm. The results of stability tests indicated that both acid (or base) resistance and thermal tolerance of GOD/CAT@IO-SiO₂ were improved. When GOD/CAT@IO-SiO₂ was used to remove glucose from commercial isomaltooligosaccharide (IMO), the immobilized bi-enzyme system exhibited the good performance. The removal efficiency of glucose reached up to 98.97% under the conditions of GOD/CAT activity ratio of 1:30, the amount of enzyme of 68.8mg, reaction time of 9.39h, reaction temperature of 35.2°C and pH of 7.05. After reused 6 times, 79.19% of removal efficiency could be still retained. The present work demonstrates that the immobilized bi-enzyme (GOD/CAT@IO-SiO₂) is not only a very promising system for glucose removal but also has great potential for applications in production of gluconic acid, preparation of biosensors, enzyme bioreactors, etc.