Current and prospective applications of metal ion-protein binding

Limits of Non-invasive Enzymatic Activation by Local Temperature Control

Enzymatic activity depends on and can therefore be regulated by temperature. Selective modulation of the activity of different enzymes in one reaction pot would require temperature control local to each type of enzyme. It has been suggested previously that immobilization of enzyme on magnetic nanoparticles and exposing them to alternating magnetic field can enhance the reaction rate. This enhancement has been explained as being mediated by temperature increase caused by dissipation of the absorbed field energy in the form of heat. However, the possibility of spatially limiting this temperature increase on the microscale has been questioned. Here, it is investigated whether an activity enhancement of the enzyme sucrose phosphorylase immobilized on magnetic beads can be achieved, how this effect is related to the increase in temperature, and whether temperature differences within one reaction pot could be generated in this way. It is found that alternating magnetic field stimulation leads to increased enzymatic activity fully attributable to the increase of bulk temperature. Both theoretical analysis and experimental data indicate that no local heating near the particle surface takes place. It is further concluded that relevant increase of surface temperature can be obtained only with macroscopic, millimeter-sized, magnetic particles.

Copper-Chelated Chitosan Microgels for the Selective Enrichment of Small Cationic Peptides

Copper-chelated chitosan microgels were investigated as an immobilized metal affinity chromatography (IMAC) phase for peptide separation. The copper-crosslinked chitosan beads were shown to strongly interact with a range of amino acids, in a wide range of pH and saline conditions. The beads exhibited an affinity that seemed to depend on the isoelectric point of the amino acid, with the extent of uptake increasing with decreasing isoelectric point. This selective interaction with anionic amino acids resulted in a significant relative enrichment of the supernatant solution in cationic amino acids. The beads were then studied as a novel fractionation system for complex milk hydrolysates. The copper chitosan beads selectively removed larger peptides from the hydrolysate aqueous solution, yielding a solution relatively enriched in medium and smaller peptides, which was characterized both quantitatively and qualitatively by size exclusion chromatography (SEC). Liquid chromatography-mass spectrometry (LCMS) work provided comprehensive data on a peptide sequence level and showed that a depletion of the anionic peptides by the beads resulted in a relative enrichment of the cationic peptides in the supernatant solution. It could be concluded that after fractionation a dramatic relative enrichment in respect to small- and medium-sized cationic peptides in the solution, characteristics that have been linked to bioactivities, such as anti-microbial and cell-penetrating properties. The results demonstrate the use of the chitosan copper gel bead system in lab scale fractionation of complex hydrolysate mixtures, with the potential to enhance milk hydrolysate bioactivity.

A High-Performance Food Package Material Prepared by the Synergistic Crosslinking of Gelatin with Polyphenol-Titanium Complexes

This study aims to enhance gelatin film performance in the food industry by incorporating polyphenol-titanium complexes (PTCs) as crosslinkers. PTCs introduce multiple linkages with gelatin, including coordination and hydrogen bonds, resulting in synergistic crosslinking effects. This leads to an increased hydrodynamic volume, particle size, and thermal stability of the gelatin films. Compared to films crosslinked solely by polyphenols or titanium, PTC-crosslinked gelatin films exhibit significant improvements. They show enhanced mechanical properties with a tensile strength that is 1.7 to 2.6 times higher than neat gelatin films. Moreover, these films effectively shield UV light (from 82% to 99%), providing better protection for light-sensitive food ingredients and preserving lutein content (from 74.2% to 78.1%) under light exposure. The incorporation of PTCs also improves film hydrophobicity, as indicated by water contact angles ranging from 115.3° to 131.9° and a water solubility ranging from 31.5% to 33.6%. Additionally, PTC-enhanced films demonstrate a superior antioxidant ability, with a prolonged polyphenol release (up to 18 days in immersed water) and a higher free radical scavenging ability (from 22% to 25.2%). Overall, the improved characteristics of gelatin films enabled by PTCs enhance their performance, making them suitable for various food packaging applications.

Isolation and molecular characterization of an FSK2-type dehydrin from Atriplex halimus

Dehydrins form the group II LEA protein family and are known to play multiple roles in plant stress tolerance and enzyme protection. They harbor a variable number of conserved lysine rich motifs (K-segments) and may also contain three additional conserved motifs (Y-, F- and S-segments). In this work, we report the isolation and characterization of an FSK₂-type dehydrin from the halophytic species Atriplex halimus, which we designate as AhDHN1. In silico analysis of the protein sequence revealed that AhDHN1 contains large number of hydrophilic residues, and is predicted to be intrinsically disordered. In addition, it has an FSK₂ architecture with one F-segment, one S-segment, and two K-segments. The expression analysis showed that the AhDHN1 transcript is induced by salt and water stress treatments in the leaves of Atriplex seedlings. Moreover, circular dichroism spectrum performed on recombinant AhDHN1 showed that the dehydrin lacks any secondary structure, confirming its intrinsic disorder nature. However, there is a gain of α-helicity in the presence of membrane-like SDS micelles. In vitro assays revealed that AhDHN1 is able to effectively protect enzymatic activity of the lactate dehydrogenase against cold, heat and dehydration stresses. Our findings strongly suggest that AhDHN1 can be involved in the adaptation mechanisms of halophytes to adverse environments.

The choice of chromatographic resin for the purification of recombinant lysostaphin affects its activity

Lysostaphin is a zinc-dependent endopeptidase that is effective against both antibiotic-sensitive and antibiotic-resistant strains of Staphylococcus aureus. Lysostaphin is typically purified on cation-exchange or metal-chelate affinity resins, and there are data indicating potential influence of the chromatographic resin on the lysostaphin activity. In this study, we systematically investigated the impact of the resin used to purify the recombinant lysostaphin on its activity. To this end, recombinant lysostaphin with an additional histidine tag at the C-terminus was purified using a cation-exchange resin, three types of nickel-chelate resins with different strength of metal ion binding, or a zinc-chelate resin. Lysostaphin samples purified on the cation-exchange resin (WorkBeads 40S), the nickel-chelate resin with the strong nickel ion binding (WorkBeads NiMAC), and the zinc-chelate resin (WorkBeads NTA with immobilized zinc ions) had equal activity. On the contrary, the activity of lysostaphin preparations purified on nickel-chelate resins with medium (WorkBeads Ni-NTA) and relatively weak (WorkBeads Ni-IDA) nickel ion binding was significantly reduced. The decrease in activity can be explained by the interaction of lysostaphin with the nickel ions leached from the resin and is caused by either the exchange of the zinc ion in the lysostaphin active center with a nickel ion from the resin, or binding of an additional ion that inhibits the enzymatic activity. Removal of metal ions from the active site of lysostaphin and subsequent incorporation of the native zinc ions lead to complete restoration of the activity of the enzyme.

Magnetic metal-organic frameworks immobilized enzyme-based nano-biocatalytic systems for sustainable biotechnology

Nanobiocatalysts, in which enzyme molecules are integrated into/onto multifunctional materials, such as metal-organic frameworks (MOFs), have been fascinating and appeared as a new interface of nanobiocatalysis with multi-oriented applications. Among various nano-support matrices, functionalized MOFs with magnetic attributes have gained supreme interest as versatile nano-biocatalytic systems for organic bio-transformations. From the design (fabrication) to deployment (application), magnetic MOFs have manifested notable efficacy in manipulating the enzyme microenvironment for robust biocatalysis and thus assure requisite applications in several areas of enzyme engineering at large and nano-biocatalytic transformations, in particular. Magnetic MOFs-linked enzyme-based nano-biocatalytic systems offer chemo-regio- and stereo-selectivities, specificities, and resistivities under fine-tuned enzyme microenvironments. Considering the current sustainable bioprocesses demands and green chemistry needs, we reviewed synthesis chemistry and application prospects of magnetic MOFs-immobilized enzyme-based nano-biocatalytic systems for exploitability in different industrial and biotechnological sectors. More specifically, following a thorough introductory background, the first half of the review discusses various approaches to effectively developed magnetic MOFs. The second half mainly focuses on MOFs-assisted biocatalytic transformation applications, including biodegradation of phenolic compounds, removal of endocrine disrupting compounds, dye decolorization, green biosynthesis of sweeteners, biodiesel production, detection of herbicides and screening of ligands and inhibitors.

Histidine-based coordinative polymers for efficient intracellular protein delivery via enhanced protein binding, cellular uptake, and endosomal escape

Polymers are one of the most promising protein delivery carriers; however, their applications are hindered by low delivery efficacy owing to their undesirable performance in protein binding, cellular uptake and endosomal escape. Here, we designed a series of histidine-based coordinative polymers for efficient intracellular protein delivery. Coordination of metal ions such as Ni²⁺, Zn²⁺, and Cu²⁺ with histidine residues on a polymer greatly improved its performance in protein binding, complex stability, cellular uptake and endosomal escape, therefore achieving highly improved protein delivery efficacy. Among the coordinative polymers, the Zn²⁺-coordinated one exhibited the highest cellular uptake, while the Cu²⁺-coordinated one exhibited the highest endosomal escape. The Ni²⁺-coordinated polymer formed large-sized aggregates with cargo proteins and showed insufficient protein release after endocytosis. The results obtained in this study provided new insight into the development of coordinative polymer-based protein delivery systems.

Preparation of Polyacrylonitrile-Based Immobilized Copper-Ion Affinity Membranes for Protein Adsorption

A polyacrylonitrile (PAN)-based immobilized metal-ion affinity membrane (IMAM) was prepared with a high capacity for protein adsorption. PAN was selected as the substrate due to its excellent thermal and chemical stability. The cyano groups on the PAN membrane were substituted with carboxyl groups, followed by reactions with ethylenediamine (EDA) and ethylene glycol diglycidyl ether (EGDGE) to produce the terminal epoxy groups. The chelating agent iminodiacetic acid (IDA) was then bound to the modified PAN membrane and further chelated with copper ions. The immobilized copper ion amount of membrane was analyzed to obtain the optimal reaction conditions, which were 60 °C/3 h for EDA coupling and 60 °C/4 h for EGDGE grafting. Furthermore, under the use of minor IDA and copper ion concentrations, the immobilized copper ion capacity of the IMAM was 4.8 μmol/cm² (253.4 µmol/mL, or 1.47 μmol/mg). At a neutral pH, the cationic lysozyme exhibited a large adsorption capacity with the IMAM (1.96 μmol/mL), which was most likely multilayer binding, whereas the adsorption capacity for bovine serum albumin (BSA) and histidine-tagged green fluorescent protein (GFP-His₆) was 0.053 μmol/mL and 0.135 μmol/mL, respectively, with a monolayer adsorption arrangement. The protein desorption efficiency was greater than 95%, implying that the prepared IMAM could be reused for protein adsorption.

Collagen and Silk Fibroin as Promising Candidates for Constructing Catalysts

A catalyst determines the mechanism of an organic chemical reaction, thus enabling the commercially viable formation of desired material products. Biopolymers offer new opportunities for the construction of catalysts by virtue of their biocompatibility, environmental benignity, and sustainability, as well as their low cost. Biopolymers are especially useful as carriers and precursors in catalysis application. The employment of biocompatible and biosustainable collagen and silk fibroin materials will revolutionize state-of-the-art electronic devices and systems that currently rely on conventional technologies. In this review, we first consider the ordered hierarchical structure, origin, and processing methods of collagen and silk fibroin. Then, the unique advantages and applicability of collagen and silk fibroin for constructing catalysts are summarized. Moreover, a summary of the state-of-the-art design, fabrication, and application of collagen- and silk fibroin-based catalysts, as well as the application of collagen- and silk-based catalysts, is presented by focusing on their roles as carriers and precursors, respectively. Finally, challenges and prospects are assessed for the construction and development of collagen and silk fibroin-based catalysts.

Tagging Recombinant Proteins to Enhance Solubility and Aid Purification

Protein fusion technology has had a major impact on the efficient production and purification of individual recombinant proteins. The use of genetically engineered affinity and solubility-enhancing polypeptide "tags" has a long history, and there is a considerable repertoire of these that can be used to address issues related to the expression, stability, solubility, folding, and purification of their fusion partner. In the case of large-scale proteomic studies, the development of purification procedures tailored to individual proteins is not practicable, and affinity tags have become indispensable tools for structural and functional proteomic initiatives that involve the expression of many proteins in parallel. In this chapter, the rationale and applications of a range of established and more recently developed solubility-enhancing and affinity tags is described.

Metal-Chelating Peptides Separation Using Immobilized Metal Ion Affinity Chromatography: Experimental Methodology and Simulation

Metal-Chelating Peptides (MCPs), obtained from protein hydrolysates, present various applications in the field of nutrition, pharmacy, cosmetic etc. The separation of MCPs from hydrolysates mixture is challenging, yet, techniques based on peptide-metal ion interactions such as Immobilized Metal Ion Affinity Chromatography (IMAC) seem to be efficient. However, separation processes are time consuming and expensive, therefore separation prediction using chromatography modelling and simulation should be necessary. Meanwhile, the obtention of sorption isotherm for chromatography modelling is a crucial step. Thus, Surface Plasmon Resonance (SPR), a biosensor method efficient to screen MCPs in hydrolysates and with similarities to IMAC might be a good option to acquire sorption isotherm. This review highlights IMAC experimental methodology to separate MCPs and how, IMAC chromatography can be modelled using transport dispersive model and input data obtained from SPR for peptides separation simulation.

Augmenting apoptosis-mediated anticancer activity of lactoperoxidase and lactoferrin by nanocombination with copper and iron hybrid nanometals

There is an urgent need in the medicinal fields to discover biocompatible nanoformulations with low cytotoxicity, which provide new strategies for promising therapies for several types of tumors. Bovine lactoperoxidase (LP) and lactoferrin (LF) have recently attracted attention in medicine for their antitumor activities with recognized safety pattern. Both LP and LF are suitable proteins to be coated or adsorbed to Cu and Fe nanometals for developing stable nanoformulations that boost immunity and strong anticancer effects. New nanometals of Cu and Fe NPs embedded in LP and LF forming novel nanocombinations of LP-CNPs and LF-FNPs had a spherical shape with an average nanosize of about 21 nm. The combination of LP-CNPs and LF-FNPs significantly exhibited the highest growth inhibitory efficacy, in terms of effectively lowering the half-maximal inhibitory concentration (IC₅₀) values, against Caco-2, HepG2 and MCF7 cells comparing to nanometals, LP, LF and individual nanoproteins (LP-CNPs or LF-FNPs). The highest apoptotic effect of this nanocombination (LP-CNPs and LF-FNPs) was confirmed by the highest percentages of annexin-stained apoptotic cells and G0 population with the strongest alteration in the expression of two well-characterized apoptosis guards (p53 and Bcl-2) and the maximum suppression in the proliferation marker (Ki-67). Also, the in silico analysis predicted that LP-CNPs and LF-FNPs enhanced AMP-activated protein kinase (AMPK, p53 activator) activity and inhibited cancer migration-related proteases (cathepsin B and matrix metalloproteinase (MMP)-9). Our results offer for the first time that these novel nanocombinations of LP and LF were superior in their selectivity and apoptosis-mediating anticancer activity to Cu and Fe nanometals as well as the free form of these proteins or their individual nanoforms.

Cu2+-Chelating Mesoporous Silica Nanoparticles for Synergistic Chemotherapy/Chemodynamic Therapy

In this study, a pH-responsive controlled-release mesoporous silica nanoparticle (MSN) formulation was developed. The MSNs were functionalized with a histidine (His)-tagged targeting peptide (B3int) through an amide bond, and loaded with an anticancer drug (cisplatin (CP)) and a lysosomal destabilization mediator (chloroquine (CQ)). Cu²⁺ was then used to seal the pores of the MSNs via chelation with the His-tag. The resultant nanoparticles showed pH-responsive drug release, and could effectively target tumor cells via the targeting effect of B3int. The presence of CP and Cu²⁺ permits reactive oxygen species to be generated inside cells; thus, the chemotherapeutic effect of CP is augmented by chemodynamic therapy. In vitro and in vivo experiments showed that the nanoparticles are able to effectively kill tumor cells. An in vivo cancer model revealed that the nanoparticles increase apoptosis in tumor cells, and thereby diminish the tumor volume. No off-target toxicity was noted. It thus appears that the functionalized MSNs developed in this work have great potential for targeted, synergistic anticancer therapies.

In Silico Characterisation of the Late Embryogenesis Abundant (LEA) Protein Families and Their Role in Desiccation Tolerance in Ramonda serbica Panc

Ramonda serbica Panc. is an ancient resurrection plant able to survive a long desiccation period and recover metabolic functions upon watering. The accumulation of protective late embryogenesis abundant proteins (LEAPs) is a desiccation tolerance hallmark. To propose their role in R. serbica desiccation tolerance, we structurally characterised LEAPs and evaluated LEA gene expression levels in hydrated and desiccated leaves. By integrating de novo transcriptomics and homologues LEAP domains, 318 R. serbica LEAPs were identified and classified according to their conserved motifs and phylogeny. The in silico analysis revealed that hydrophilic LEA4 proteins exhibited an exceptionally high tendency to form amphipathic α-helices. The most abundant, atypical LEA2 group contained more hydrophobic proteins predicted to fold into the defined globular domains. Within the desiccation-upregulated LEA genes, the majority encoded highly disordered DEH1, LEA1, LEA4.2, and LEA4.3 proteins, while the greatest portion of downregulated genes encoded LEA2.3 and LEA2.5 proteins. While dehydrins might chelate metals and bind DNA under water deficit, other intrinsically disordered LEAPs might participate in forming intracellular proteinaceous condensates or adopt amphipathic α-helical conformation, enabling them to stabilise desiccation-sensitive proteins and membranes. This comprehensive LEAPs structural characterisation is essential to understanding their function and regulation during desiccation aiming at crop drought tolerance improvement.

Extracellular Secretion and Simple Purification of Bacterial Collagen from Escherichia coli

Because of structural similarities with type-I animal collagen, recombinant bacterial collagen-like proteins have been progressively used as a source of collagen for biomaterial applications. However, the intracellular expression combined with current costly and time-consuming chromatography methods for purification makes the large-scale production of recombinant bacterial collagen challenging. Here, we report the use of an adapted secretion pathway, used natively byEscherichia colito secrete curli fibers, for extracellular secretion of the bacterial collagen. We confirmed that a considerable fraction of expressed collagen (∼70%) is being secreted freely into the extracellular medium, with an initial purity of ∼50% in the crude culture supernatant. To simplify the purification of extracellular collagen, we avoided cell lysis and used cross-flow filtration or acid precipitation to concentrate the voluminous supernatant and separate the collagen from impurities. We confirmed that the secreted collagen forms triple helical structures, using Sirius Red staining and circular dichroism. We also detected collagen biomarkers via Raman spectroscopy, further supporting that the recombinant collagen forms a stable triple helical conformation. We further studied the effect of the isolation methods on the morphology and secondary structure, concluding that the final collagen structure is process-dependent. Overall, we show that the curli secretion system can be adapted for extracellular secretion of the bacterial collagen, eliminating the need for cell lysis, which simplifies the collagen isolation process and enables a simple cost-effective method with potential for scale-up.

Protein Nanoparticles: Uniting the Power of Proteins with Engineering Design Approaches

Protein nanoparticles, PNPs, have played a long-standing role in food and industrial applications. More recently, their potential in nanomedicine has been more widely pursued. This review summarizes recent trends related to the preparation, application, and chemical construction of nanoparticles that use proteins as major building blocks. A particular focus has been given to emerging trends related to applications in nanomedicine, an area of research where PNPs are poised for major breakthroughs as drug delivery carriers, particle-based therapeutics or for non-viral gene therapy.

Design and Synthesis of Porphyrin-Nitrilotriacetic Acid Dyads with Potential Applications in Peptide Labeling through Metallochelate Coupling

The need to detect and monitor biomolecules, especially within cells, has led to the emerging growth of fluorescent probes. One of the most commonly used labeling techniques for this purpose is reversible metallochelate coupling via a nitrilotriacetic acid (NTA) moiety. In this study, we focus on the synthesis and characterization of three new porphyrin-NTA dyads, TPP-Lys-NTA, TPP-CC-Lys-NTA, and Py ₃ P-Lys-NTA composed of a porphyrin derivative covalently connected with a modified nitrilotriacetic acid chelate ligand (NTA), for possible metallochelate coupling with Ni²⁺ ions and histidine sequences. Emission spectroscopy studies revealed that all of the probes are able to coordinate with Ni²⁺ ions and consequently can be applied as fluorophores in protein/peptide labeling applications. Using two different histidine-containing peptides as His₆-tag mimic, we demonstrated that the porphyrin-NTA hybrids are able to coordinate efficiently with the peptides through the metallochelate coupling process. Moving one step forward, we examined the ability of these porphyrin-peptide complexes to penetrate and accumulate in cancer cells, exploring the potential utilization of our system as anticancer agents.

Data-rich process development of immobilized biocatalysts in flow

The authors describe an automated, data-rich screening and process development method for rapid discovery, development, and optimization of immobilized enzymes, critical to many biocatalytic processes.

Engineered Stable 5-Hydroxymethylfurfural Oxidase (HMFO) from 8BxHMFO Variant of Methylovorus sp. MP688 through B-Factor Analysis

What is known as Furan-2,5-dicarboxylic acid (FDCA) is an attractive compound since it has similar properties to terephthalic acid. Further, 5-hydroxymethylfurfural oxidase (HMFO) is an enzyme, which could convert HMF to FDCA directly. Most wild types of HMFO have low activity on the oxidation of HMF to FDCA. The variant of 8BxHFMO from Methylovorus sp. MP688 was the only reported enzyme that was able to perform FDCA production. However, the stabilization of 8BxHMFO is still not that satisfactory, and further improvement is necessary for the industrial application of the enzyme. In this work, stability-enhanced HMFO from 8BxHFMO was engineered through employing B-factor analysis. The mutation libraries were created based on the NNK degeneracy of residues with the top ten highest B-factor value, and two of the effective mutants were screened out through the high throughput selection with the horseradish peroxidase (HRP)-Tyr assay. The mutants Q319K and N44G show a significantly increased yield of FDCA in the reaction temperature range of 30 to 40 °C. The mutant Q319K shows the best performance at 35 °C with a FDCA yield of 98% (the original 8BxHMFO was only 85%), and a half-life exceeding 72 h. Moreover, molecular dynamic simulation indicates that more hydrogen bonds are formed in the mutants, which improves the stability of the protein structure. The method could enhance the design of more stable biocatalysts; and provides potential for the further optimization and utilization of HMFO in biotechnological processes.

Metal-Coordinated Supramolecular Self-Assemblies for Cancer Theranostics

Metal-coordinated supramolecular nanoassemblies have recently attracted extensive attention as materials for cancer theranostics. Owing to their unique physicochemical properties, metal-coordinated supramolecular self-assemblies can bridge the boundary between traditional inorganic and organic materials. By tailoring the structural components of the metal ions and binding ligands, numerous multifunctional theranostic nanomedicines can be constructed. Metal-coordinated supramolecular nanoassemblies can modulate the tumor microenvironment (TME), thus facilitating the development of TME-responsive nanomedicines. More importantly, TME-responsive organic-inorganic hybrid nanomaterials can be constructed in vivo by exploiting the metal-coordinated self-assembly of a variety of functional ligands, which is a promising strategy for enhancing the tumor accumulation of theranostic molecules. In this review, recent advancements in the design and fabrication of metal-coordinated supramolecular nanomedicines for cancer theranostics are highlighted. These supramolecular compounds are classified according to the order in which the coordinated metal ions appear in the periodic table. Furthermore, the prospects and challenges of metal-coordinated supramolecular self-assemblies for both technical advances and clinical translation are discussed. In particular, the superiority of TME-responsive nanomedicines for in vivo coordinated self-assembly is elaborated, with an emphasis on strategies that enhance the accumulation of functional components in tumors for an ideal theranostic outcome.

Development of a Bio-Layer Interferometry-Based Protease Assay Using HIV-1 Protease as a Model

Proteolytic enzymes have great significance in medicine and the pharmaceutical industry and are applied in multiple fields of life sciences. Therefore, cost-efficient, reliable and sensitive real-time monitoring methods are highly desirable to measure protease activity. In this paper, we describe the development of a new experimental approach for investigation of proteolytic enzymes. The method was designed by the combination of recombinant fusion protein substrates and bio-layer interferometry (BLI). The protease (PR) of human immunodeficiency virus type 1 (HIV-1) was applied as model enzyme to set up and test the method. The principle of the assay is that the recombinant protein substrates immobilized to the surface of biosensor are specifically cleaved by the PR, and the substrate processing can be followed by measuring change in the layer thickness by optical measurement. We successfully used this method to detect the HIV-1 PR activity in real time, and the initial rate of the signal decrease was found to be proportional to the enzyme activity. Substrates representing wild-type and modified cleavage sites were designed to study HIV-1 PR's specificity, and the BLI-based measurements showed differential cleavage efficiency of the substrates, which was proven by enzyme kinetic measurements. We applied this BLI-based assay to experimentally confirm the existence of extended binding sites at the surface of HIV-1 PR. We found the measurements may be performed using lysates of cells expressing the fusion protein, without primary purification of the substrate. The designed BLI-based protease assay is high-throughput-compatible and enables real-time and small-volume measurements, thus providing a new and versatile approach to study proteolytic enzymes.

Design and Development of Antibody Functionalized Gold Nanoparticles for Biomedical Applications

Antibody-functionalized gold nanoparticle constitutes a powerful interface biosystem for biomedical applications where the properties of gold nanoparticles and the specificity of antibody-antigen interactions are combined. This study provides insight into the key factors for the development of antibody functionalized gold nanoparticles focusing on the immobilization of the antibody. Here, we address an oriented antibody immobilization procedure on gold nanoparticles. It comprises chelatemodified gold nanoparticles that are designed for oriented immobilization of IgG antibodies (end on spatial orientation) through the metal-chelation to histidine-rich metal binding site in the heavy chain (Fc) of the antibody.

Co-immobilized Alcohol Dehydrogenase and Glucose Dehydrogenase with Resin Extraction for Continuous Production of Chiral Diaryl Alcohol

Ni²⁺-functionalized porous ceramic/agarose composite beads (Ni-NTA Cerose) can be used as carrier materials to immobilize enzymes harboring a metal affinity tag. Here, a 6×His-tag fusion alcohol dehydrogenase Mu-S5 and glucose dehydrogenase from Bacillus megaterium (BmGDH) were co-immobilized on Ni-NTA Cerose to construct a packed bed reactor (PBR) for the continuous synthesis of the chiral intermediate (S)-(4-chlorophenyl)-(pyridin-2-yl) methanol ((S)-CPMA) NADPH recycling, and in situ product adsorption was achieved simultaneously by assembling a D101 macroporous resin column after the PBR. Using an optimum enzyme activity ratio of 2:1 (Mu-S5: BmGDH) and hydroxypropyl-β-cyclodextrin as co-solvent, a space-time yield of 1560 g/(L·d) could be achieved in the first three days at a flow rate of 5 mL/min and substrate concentration of 10 mM. With simplified selective adsorption and extraction procedures, (S)-CPMA was obtained in 84% isolated yield.

Possible Action of Transition Divalent Metal Ions at the Inter-Pentameric Interface of Inactivated Foot-and-Mouth Disease Virus Provide A Simple but Effective Approach to Enhance Stability

The structural instability of inactivated foot-and-mouth disease virus (FMDV) hinders the development of vaccine industry. Here we found that some transition metal ions like Cu²⁺ and Ni²⁺ could specifically bind to FMDV capsids at capacities about 7089 and 3448 metal ions per capsid, respectively. These values are about 33- and 16-folds of the binding capacity of non-transition metal ion Ca²⁺ (about 214 per capsid). Further thermodynamic studies indicated that all these three metal ions bound to the capsids in spontaneous enthalpy driving manners (ΔG<0, ΔH<0, ΔS<0), and the Cu²⁺ binding had the highest affinity. The binding of Cu²⁺ and Ni²⁺ could enhance both the thermostability and acid-resistant stability of capsids, while the binding of Ca²⁺ was helpful only to the thermostability of the capsids. Animal experiments showed that the immunization of FMDV bound with Cu²⁺ induced the highest specific antibody titers in mice. Coincidently, the FMDV bound with Cu²⁺ exhibited significantly enhanced affinities to integrin β6 and heparin sulfate, both of which are important cell surface receptors for FMDV attaching. Finally, the specific interaction between capsids and Cu²⁺ or Ni²⁺ was applied to direct purification of FMDV from crude cell culture feedstock by the immobilized metal affinity chromatography. Based on our new findings and structural analysis of the FMDV capsid, a "transition metal ion bridges" mechanism that describes linkage between adjacent histidine and other amino acids at the inter-pentameric interface of the capsids by transition metal ions coordination action was proposed to explain their stabilizing effect imposed on the capsid.IMPORTANCE How to stabilize the inactivated FMDV without affecting virus infectivity and immunogenicity is a big challenge in vaccine industry. The electrostatic repulsion induced by protonation of a large amount of histidine residues at the inter-pentameric interface of viral capsids is one of the major mechanisms causing the dissociation of capsids. In the present work, this structural disadvantage inspired us to stabilize the capsids through coordinating transition metal ions with the adjacent histidine residues in FMDV capsid, instead of removing or substituting them. This approach was proved effective to enhance not only the stability of FMDV, but also enhance the specific antibody responses; thus, providing a new guideline for designing an easy-to-use strategy suitable for large-scale production of FMDV vaccine antigen.

Isolation and Sequencing of Cu-, Fe-, and Zn-Binding Whey Peptides for Potential Neuroprotective Applications as Multitargeted Compounds

This study aims to isolate metal-binding peptides and synthesize promising amino acid sequences to potentially act as neuroprotective compounds in the future, targeting different mechanisms. Fractions of whey metal-binding peptides (Cu, Fe, and Zn) isolated by immobilized metal affinity chromatography showed different amino acid profiles according to the metal. The Cu-binding peptides presented roughly twofold increase in the in vitro antioxidant, as assessed by oxygen radical absorbance capacity and anticholinesterase activities over the hydrolysate. This is probably because of the higher concentration of aromatic and basic residues, the latter being crucial for binding to the anionic sites of acetylcholinesterase. Six peptide sequences were synthesized based on the metal-binding sites, molecular mass, hydrophobicity, and bioactivity probability. Among the synthetic peptides, the VF dipeptide stood out both for its in vitro antioxidant and anticholinesterase activities. This peptide, as well as the fraction of Cu-binding peptides, should be further studied because it may act through different mechanisms related to neurodegenerative diseases, in addition to the chelation of the excess of metals in the central nervous system.

Smart Molecular Nanosheets for Advanced Preparation of Biological Samples in Electron Cryo-Microscopy

Transmission electron cryo-microscopy (cryoEM) of vitrified biological specimens is a powerful tool for structural biology. Current preparation of vitrified biological samples starts off with sample isolation and purification, followed by the fixation in a freestanding layer of amorphous ice. Here, we demonstrate that ultrathin (∼10 nm) smart molecular nanosheets having specific biorecognition sites embedded in a biorepulsive layer covalently bound to a mechanically stable carbon nanomembrane allow for a much simpler isolation and structural analysis. We characterize in detail the engineering of these nanosheets and their biorecognition properties employing complementary methods such as X-ray photoelectron and infrared spectroscopy, atomic force microscopy as well as surface plasmon resonance measurements. The desired functionality of the developed nanosheets is demonstrated by in situ selection of a His-tagged protein from a mixture and its subsequent structural analysis by cryoEM.

Role of carboxylic group pattern on protein surface in the recognition of iron oxide nanoparticles: A key for protein corona formation

The knowledge of protein-nanoparticle interplay is of crucial importance to predict the fate of nanomaterials in biological environments. Indeed, protein corona on nanomaterials is responsible for the physiological response of the organism, influencing cell processes, from transport to accumulation and toxicity. Herein, a comparison using four different proteins reveals the existence of patterned regions of carboxylic groups acting as recognition sites for naked iron oxide nanoparticles. Readily interacting proteins display a distinctive surface distribution of carboxylic groups, recalling the geometric shape of an ellipse. This is morphologically complementary to nanoparticles curvature and compatible with the topography of exposed Fe^III sites laying on the nanomaterial surface. The recognition site, absent in non-interacting proteins, promotes the nanoparticle harboring and allows the formation of functional protein coronas. The present work envisages the possibility of predicting the composition and the biological properties of protein corona on metal oxide nanoparticles.

A Novel Particulate Delivery System Based on Antigen-Zn2+ Coordination Interactions Enhances Stability and Cellular Immune Response of Inactivated Foot and Mouth Disease Virus

The interactions between antigen and adjuvant were among the most significant factors influencing the immunogenicity of vaccines, especially for unstable antigens like inactivated foot and mouth disease virus (iFMDV). Here we propose a novel antigen delivery pattern based on the coordination interaction between transition metal ions Zn²⁺ chelated to chitosan nanoparticles and iFMDV, which is known to be rich in histidine. The zinc chelated chitosan particles (CP-PEI-Zn) were prepared by cross-linking chitosan particles (CP) with sodium tripolyphosphate (TPP), modifying with metal chelator polyethylenimine (PEI), and subsequent chelating of Zn²⁺. The coordination interaction was confirmed by analyzing the adsorption and desorption behavior of iFMDV on CP-PEI-Zn by high-performance size exclusion chromatography (HPSEC), while the CP-PEI without chelating Zn²⁺ loads iFMDV mainly through electrostatic interactions. The iFMDV loaded on CP-PEI-Zn showed better thermal stability than that on CP-PEI, as revealed by a slightly higher transition temperature (T_m) related to iFMDV dissociation. After subcutaneous immunization in female Balb/C mice, antigens loaded on CP-PEI and CP-PEI-Zn all induced higher specific antibody titers, better activation of B lymphocytes, and more effector-memory T cells proliferation than the free antigen and iFMDV adjuvanted with ISA 206 emulsion did. Moreover, CP-PEI-Zn showed superior efficacy to CP-PEI in promoting the proliferation of effector-memory T cells and secretion of cytokines, indicating a more potent cellular immune response. In summary, the CP-PEI-Zn stabilized the iFMDV after loading and promoted both humoral and cellular immune responses, thus reflecting its potential to be a promising adjuvant for the iFMDV vaccine and other unstable viral antigens.

Alcalase Microarray Base on Metal Ion Modified Hollow Mesoporous Silica Spheres as a Sustainable and Efficient Catalysis Platform for Proteolysis

The industrial exploitation of protease is limited owing to its sensitivity to environmental factors and autolysis during biocatalytic processes. In the present study, the alcalase microarray (Bacillus licheniformis, alcalase@HMSS-NH₂-Metal) based on different metal ions modified hollow mesoporous silica spheres (HMSS-NH₂-Metal) was successfully developed via a facile approach. Among the alcalase@HMSS-NH₂-Metal (Ca²⁺, Zn²⁺, Fe³⁺, Cu²⁺), the alcalase@HMSS-NH₂-Fe³⁺ revealed the best immobilization efficiency and enzymatic properties. This tailor-made nanocomposite immobilized alcalase on a surface-bound network of amino-metal complex bearing protein-modifiable sites via metal-protein affinity. The coordination interaction between metal ion and alcalase advantageously changed the secondary structure of enzyme, thus significantly enhanced the bioactivities and thermostability of alcalase. The as-prepared alcalase@HMSS-NH₂-Fe³⁺ exhibited excellent loading capacity (227.8 ± 23.7 mg/g) and proteolytic activity. Compared to free form, the amidase activity of alcalase microarray increased by 5.3-fold, the apparent kinetic constant V_max/K_m of alcalase@HMSS-NH₂-Fe³⁺ (15.6 min⁻¹) was 1.9-fold higher than that of free alcalase, and the biocatalysis efficiency increased by 2.1-fold for bovine serum albumin (BSA) digestion. Moreover, this particular immobilization strategy efficiently reduced the bioactivities losses of alcalase caused by enzyme leaking and autolysis during the catalytic process. The alcalase microarray still retained 70.7 ± 3.7% of the initial activity after 10 cycles of successive reuse. Overall, this study established a promising strategy to overcome disadvantages posed by free alcalase, which provided new expectations for the application of alcalase in sustainable and efficient proteolysis.

Peptide-metal complexes: obtention and role in increasing bioavailability and decreasing the pro-oxidant effect of minerals

Bioactive peptides derived from food protein sources have been widely studied in the last years, and scientific researchers have been proving their role in human health, beyond their nutritional value. Several bioactivities have been attributed to these peptides, such as immunomodulatory, antimicrobial, antioxidant, antihypertensive, and opioid. Among them, metal-binding capacity has gained prominence. Mineral chelating peptides have shown potential to be applied in food products so as to decrease mineral deficiencies since peptide-metal complexes could enhance their bioavailability. Furthermore, many studies have been investigating their potential to decrease the Fe pro-oxidant effect by forming a stable structure with the metal and avoiding its interaction with other food constituents. These complexes can be formed during gastrointestinal digestion or can be synthesized prior to intake, with the aim to protect the mineral through the gastrointestinal tract. This review addresses: (i) the amino acid residues for metal-binding peptides and their main protein sources, (ii) peptide-metal complexation prior to or during gastrointestinal digestion, (iii) the function of metal (especially Fe, Ca, and Zn)-binding peptides on the metal bioavailability and (iv) their reactivity and possible pro-oxidant and side effects.

Expanding a Portfolio of (FO-) SPR Surface Chemistries with the Co(III)-NTA Oriented Immobilization of His6-Tagged Bioreceptors for Applications in Complex Matrices

Cobalt-nitrilotriacetic acid (Co(III)-NTA) chemistry is a recognized approach for oriented patterning of His₆-tagged bioreceptors. We have applied the matching strategy for the first time on a surface plasmon resonance (SPR) platform, namely, the commercialized fiber optic (FO)-SPR. To accomplish this, His₆-tagged bioreceptor (scFv-33H1F7) and its target PAI-1 were used as a model system, after scrutinizing the specificity of their interaction. When benchmarked to traditional carboxyl-based self-assembled monolayers (SAM), NTA allowed (1) more efficient FO-SPR surface coverage with bioreceptors compared with the former and (2) realization of thus far difficult-to-attain label-free bioassays on the FO-SPR platform in both buffer and 20-fold diluted human plasma. Moreover, Co(III)-NTA surface proved to be compatible with traditional gold nanoparticle-mediated signal amplification in the buffer as well as in 10-fold diluted human plasma, thus expanding the dynamic detection range to low ng/mL. Both types of bioassays revealed that scFv-33H1F7 immobilized on the FO-SPR surface using different concentrations (20, 10, or 5 μg/mL) had no impact on the bioassay sensitivity, accuracy, or reproducibility despite the lowest concentration effectively resulting in close to 20% fewer bioreceptors. Collectively, these results highlight the importance of Co(III)-NTA promoting the oriented patterning of bioreceptors on the FO-SPR sensor surface for securing robust and sensitive bioassays in complex matrices, both in label-free and labeled formats.

Ligand Fishing: An Approach for the Discovery of Inhibitors from Complex Biological Mixtures

Ligand fishing is a convenient bioanalytical screening method that is based on the affinity selection of a ligand from a complex biological sample by an immobilized receptor. It is a versatile affinity-based screening approach and it has found application in multiple interacting pairs such as enzyme-inhibitor/activator, antigen-antibody, receptor-ligand, and protein-protein. Important parameters that affect the successful operation of the method are the high specificity and strong binding affinity of the interacting pair (e.g., enzyme-ligand complex) and the elution of the bound ligand from the complex. This chapter provides protocols for the synthesis of affinity adsorbent and its application in off-line ligand-fishing procedure for a 6His-tagged glutathione transferase (GST).

Evaluation of Iminodiacetic Acid (IDA) as an Ionogenic Group for Adsorption of IgG1 Monoclonal Antibodies by Membrane Chromatography

Iminodiacetic acid (IDA) is one of the chelating ligands most frequently employed in immobilized metal-ion affinity chromatography (IMAC) due to its ability to act as electron-pair donor, forming stable complexes with intermediate and borderline Lewis metal ions (electron acceptor). Thus, IDA can also be employed in ion exchange chromatography to purify positively charged proteins at neutral pH values. This study aimed to evaluate IDA as an ionogenic group (ion exchanger) immobilized on poly (ethylene vinyl alcohol) (PEVA) hollow fiber membranes for immunoglobulin G₁ (IgG₁) monoclonal antibody (MAb) purification. IDA-PEVA membranes showed considerable promise for MAb purification, since IgG₁ was recovered in eluted fractions with traces of contaminants as confirmed by Western blotting and ELISA analysis. Quantification of IgG₁ showed that a purity of 94.2% was reached in the elution step. Breakthrough curve and batch adsorption experiments showed that the MAb dynamic binding capacity (DBC) of 3.10 mg g^-1 and the maximum adsorption capacity of 70 mg g^-1 were of the same order of magnitude as those found in the literature. The results obtained showed that the IDA-PEVA hollow fiber membrane could be a powerful adsorbent for integrating large-scale processes for purification of MAb from cell culture supernatant.

Tris-(Nitrilotriacetic Acid)-Decorated Polymer Conjugates as Tools for Immobilization and Visualization of His-Tagged Proteins

Recombinant proteins are commonly expressed with artificial affinity tags for purification, immobilization and characterization. The most frequently used tag, His-tag, is a sequence of consecutive histidine residues fused to the protein of interest. Specialized small molecules that bind His-tag are primarily used for purification, while antibodies are used for protein analysis. However, various issues may be encountered with the use of antibodies. Low inherent stability, the difficulty of introducing chemical modifications, and often-unreliable batch-to-batch consistency are among the limiting factors that call for better alternatives. Recently described polymer conjugates of N-(2-hydroxypropyl) methacrylamide and low-molecular-weight functional ligands, so-called iBodies, are antibody mimetics capable of replacing antibodies in biochemical applications. We tailored this system for methods utilizing His-tag by accessorizing the polymer carrier with tris-nitrilotriacetic acid targeting ligands. These anti-polyHis iBodies are additionally accessorized with fluorophores, enabling detection, and biotin ligands, enabling immobilization. Here, we characterized anti-polyHis iBodies and explored their use as antibody mimetics. We tested their stability, as well as the influence of different metal mediators and His-tag lengths on binding. With high affinity and stability, iBodies represent a new alternative for immobilization and visualization of His-tagged proteins.

Purification and Partial Characterization of Peroxidases from Three Food Waste By-Products: Broad Bean Pods, Pea Pods, and Artichoke Stems

In this study, peroxidases (PODs) from three waste by-products: broad bean pods (BBP), pea pods (PP), and artichoke stems (ARS) were purified and their optimal conditions were determined for the first time. The purification process resulted in 4.32, 7.21, and 8.9% of POD recoveries for PP, ARS, and BBP, respectively. They were purified 2.12-, 32.97-, and 10-fold with specific activities of 27.26, 266.43, and 27 U/mg of protein, respectively. Analysis of their optimal conditions showed that POD purified from BBP and PP exhibited the highest activity at 60 °C temperature and pH 6 and 8 with strong affinity with catechol substrate (Km of 0.356 and 0.189 mM; Vmax of 0.08 and 0.041 μM/min for BBP and PP, respectively). The highest activity of ARS POD was obtained under the following conditions: temperature at 50 °C, pH from 6 to 8, and guaiacol as substrate (Km 0.375 mM; Vmax 0.012 μM/min). Apart from giving the opportunity for recycling the food industry wastes, the studied waste by-products could represent an alternative source of PODs that could find several applications in the biotechnological, chemical, and food industries.