Fabrication of Raspberry-like Cytochrome C Surface-Imprinted Nanoparticles Based on MOF Composites for High-Performance Protein Separation

A general method to improve imprinting efficiency in surface protein imprinting by enhanced pre-assembly

Surface protein-imprinted nanoparticles may replace the expensive and unstable antibodies in biomedical applications but still suffers from a low imprinting efficiency. A main reason may be the insufficient pre-assembly between monomers and template protein in surface imprinting using the conventional surface graft polymerization method. Increasing monomer concentrations enhances pre-assembly, but leads to agglomeration of the particles. To solve the dilemma, here an initiating system consisting of surface-immobilized glucose oxidase and horseradish peroxidase, glucose and acetylacetone was used to synthesize the imprinted coatings. No agglomeration occurs even at high monomer concentrations because of the localized polymerization. When surface imprinting of lysozyme over silica nanoparticles, both adsorption capacity and imprinting factor increase with increasing monomer concentration, because of the enhanced pre-assembly. This strategy was further combined with the "shape-memorable imprint cavity" strategy in which the conventional crosslinker is replaced with a peptide crosslinker capable of undergoing pH-induced helix-coil transition. The resulting surface lysozyme-imprinted silica nanoparticles exhibit high adsorption capacity, high imprinting factor, high selectivity, good reusability, easy and complete template removal under mild conditions, and fast rebinding kinetics. Surface imprinting of other proteins with high imprinting efficiency were also successfully carried out, demonstrating the generality of the strategy. STATEMENT OF SIGNIFICANCE: Surface protein-imprinted nanoparticles have emerged as promising artificial antibodies, but still suffering from low imprinting efficiency, primarily due to insufficient pre-assembly between functional monomers and template proteins. Increasing monomer concentrations enhances pre-assembly but causes particle agglomeration. Here the dilemma was solved by using an initiating system consisting of surface-immobilized glucose oxidase/horseradish peroxidase, glucose, and acetylacetone to achieve localized polymerization. Imprinting efficiency was significantly improved because of enhanced pre-assembly. This strategy was further combined with the "shape-memorable imprint cavity" strategy. Lysozyme-imprinted nanoparticles with high capacity (146.4 mg g-1), high imprinting factor (13.94), reusability, and fast rebinding kinetics was synthesized. Surface imprinting of other proteins with high imprinting efficiency were also successfully carried out, demonstrating the generality of the strategy.

Unravelling the Potential of Zwitterionic Polymers in Molecular Imprinting

Molecularly imprinted polymers (MIPs) are a class of molecular receptors that are the closest imitation of biological receptors. They are often called "artificial enzymes". The capability of the MIPs to bind bioactive molecules under specific conditions creates molecular imprinting technology as having considerable potential for customized applications. Polymerization in the presence of a "template" molecule with the assistance of monomers, cross-linkers, and initiators leads to MIPs on extraction of the template molecule from the polymeric matrices. Conventionally neutral monomers were utilized for molecular imprinting. Recently, zwitterionic polymers, having innumerable advantages over nonionic polymers, were realized to be an advantageous choice as a polymeric matrix for imprinting. This review article presents an overview of sulfobetaine, carbobetaine, and phosphobetaine polymers as imprinting matrices for a range of template(s). Zwitterionic polymers are accomplished with biocompatibility, low cytotoxicity, negligible immunogenicity, systematic stability, and long circulation time, and can alleviate quick recognition by the immune system and delayed blood clearance from the body. They can be a fitting candidate for imprinting, especially of biomolecules. The molecular imprinting work on zwitterionic polymers is presented here, which will encourage researchers working in this area.

Fabricating Polymeric Micelles with Enrichment and Cavity Effect for In Situ Enzyme Imobilization from Natural Biosystems

Metal-organic frameworks and hydrogen-organic frameworks (MOFs and HOFs) are attractive hosts for enzyme immobilization, but they are limited to immobilizing the purified enzymes, making industrial upscaling unattractive. Herein, aptamer-modified dual thermoresponsive polymeric micelles with switchable self-assembly and core-shell structure are constructed, which enable selective immobilization of trypsin directly from complex biological systems through a cascade operation of separation and immobilization. Their steric self-assembly provides a large amount of adsorption sites on the soluble micellar shell, resulting in high adsorption capacity and excellent selectivity. Meanwhile, their aptamer affinity ligand and cavity maintain the native conformations of trypsin and offer protective effects even in harsh conditions. The maximum adsorption capacity of the polymeric micelles for trypsin was determined to be 197 mg/g at 60 min, superior to those of MOFs and HOFs. 67.2 and 86.6% of its original activity was retained for trypsin immobilized in the cavity under strong alkaline and acidic conditions, respectively.

Recombinant streptococcal protein G-modified metal-organic framework ZIF-8 for the highly selective purification of immunoglobulin G from human serum

A novel solid phase extractant His-rSPG@ZIF-8 was prepared by covalently coupling recombinant streptococcal protein G (His-rSPG) with ZIF-8. The His-rSPG@ZIF-8 composite was characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Due to the specific binding between the immunoglobulin binding region of His-rSPG and the Fc region of immunoglobulin G (IgG), the His-rSPG@ZIF-8 composite demonstrated exceptional selectivity in adsorbing IgG. In Britton-Robinson buffer (BR buffer) with a salt concentration of 500 mmol L-1 (0.04 mol L-1, pH 8.0), the His-rSPG@ZIF-8 composite exhibited a remarkable adsorption efficiency of 99.8 % for 0.05 mg of the composite on 200 μL of IgG solution (100 μg mL-1). The adsorption behavior of the His-rSPG@ZIF-8 composite aligns with the Langmuir adsorption model, and the theoretical maximum adsorption capacity is 1428.6 mg g-1. The adsorbed IgG molecules were successfully eluted using a SDS solution (0.5 %, m/m), resulting in a recovery rate of 91.2 %. Indeed, the His-rSPG@ZIF-8 composite was successfully utilized for the isolation and purification of IgG from human serum samples. The obtained IgG exhibited high purity, as confirmed by SDS-PAGE analysis. Additionally, LC-MS/MS analysis was employed to identify the human serum proteins following the adsorption and elution process using the His-rSPG@ZIF-8 composite material. The results revealed that the recovered solution contained an impressive content of immunoglobulin, accounting for 62.4 % of the total protein content. Furthermore, this process also led to the significant enrichment of low abundance proteins such as Serpin B4 and Cofilin-1. Consequently, the His-rSPG@ZIF-8 composite holds great promise for applications such as IgG purification and immunoassays. At the same time, it expands the application of metal-organic frameworks in the field of proteomics.

Preparation of lysozyme-imprinted mesoporous Zr-based metal-organic frameworks with remarkable specific recognition

The development of high-performance protein-imprinted materials remains challenging due to defects concerning high mass transfer resistance and non-specific binding, which are crucial for protein purification and enrichment. In this paper, lysozyme-imprinted mesoporous Zr-based MOF (mesoUiO-66-NH2@MIPs) with specific and selective recognition of lysozyme (Lyz) were prepared by surface imprinting technology. In particular, the excellent hydrophilicity mesoporous MOFs (mesoUiO-66-NH2) with a pore size of 10 nm was prepared as a carrier for Lyz immobilization by an auxiliary modulation strategy to regulate the microporous structure of UiO-66-NH2 with the propionic acid solution, enabling massive loading of the macromolecular protein Lyz. The mesoUiO-66-NH2@MIPs reached a maximum saturation adsorption of 206.54 mg g-1 on Lyz in 20 min at 25 °C with an imprinting factor of 2.57 and selection factors of 2.02, 2.34, and 2.45 for cytochrome c (Cyt c), bovine serum albumin (BSA) and bovine hemoglobin (BHb), respectively. More importantly, the mesoUiO-66-NH2@MIPs could specifically recognize Lyz from the mixed protein system. The adsorption capacity of Lyz could still reach 78.55% after 5 cycles with good cyclic regeneration performance. This provides a new research option for developing and applying novel porous MOF in biomolecule imprinting technology and the specific separation of biomolecules.

Surface ligand-assisted synthesis and biomedical applications of metal-organic framework nanocomposites

Metal-organic framework (MOF) nanocomposites have recently gained intensive attention for biosensing and disease therapy applications owing to their outstanding physiochemical properties. However, the direct growth of MOF nanocomposites is usually hindered by the mismatched lattice in the interface between the MOF and other nanocomponents. Surface ligands, molecules with surfactant-like properties, are demonstrated to exhibit the robust capability to modify the interfacial properties of nanomaterials and can be utilized as a powerful strategy for the synthesis of MOF nanocomposites. Besides this, surface ligands also exhibit significant functions in the morphological control and functionalization of MOF nanocomposites, thus greatly enhancing their performance in biomedical applications. In this review, the surface ligand-assisted synthesis and biomedical applications of MOF nanocomposites are comprehensively reviewed. Firstly, the synthesis of MOF nanocomposites is discussed according to the diverse roles of surface ligands. Then, MOF nanocomposites with different properties are listed with their applications in biosensing and disease therapy. Finally, current challenges and further directions of MOF nanocomposites are presented to motivate the development of MOF nanocomposites with elaborate structures, enriched functions, and excellent application prospects.

Anchoring of Polymer Loops on Enzyme-Immobilized Mesoporous ZIF-8 Enhances the Recognition Selectivity of Angiotensin-Converting Enzyme Inhibitory Peptides

Immobilized angiotensin-converting enzyme (ACE) is a promising material for the rapid screening of antihypertensive drugs, but the nonspecific adsorption is a serious problem in separation processes involving complex biological products. In this study, triblock copolymers with dopamine (DA) block as anchors and PEG block as the main body (DA-PEGx-DA) were attached to an immobilized ACE (ACE@mZIF-8/PDA, AmZP) surface via the “grafting to” strategy which endowed them with anti-nonspecific adsorption. The influence of DA-PEGx-DA chain length on nonspecific adsorption was confirmed. The excellent specificity and reusability of the obtained ACE@mZIF-8/PDA/DA-PEG5000-DA (AmZPP5000) was validated by screening two known ACE inhibitory peptides Val-Pro-Pro (VPP, competitive inhibitory peptides of ACE) and Gly-Met-Lys-Cys-Ala-Phe (GF-6, noncompetitive inhibitory peptides of ACE) from a mixture containing active and inactive compounds. These results demonstrate that anchored polymer loops are effective for high-recognition selectivity and AmZPP5000 is a promising compound for the efficient separation of ACE inhibitors in biological samples.

Isolation of Cytochrome C for Proteomics with Lindqvist-type Polyiodate Modified Metal Organic Framework

Separation and purification of Cytochrome C (Cyt-C) is important for proteomic. High efficient and selective pretreatment method for Cyt-C in real samples are always needed. Herein, polyniobate (K₇H[Nb₆O₁₉]·13H₂O, Nb₆O₁₉) is modified on a metal-organic framework MIL-125(Ti) through intermolecular hydrogen bonds and an aqueous-stable composite Nb₆O₁₉/MIL-125(Ti) is successfully prepared to pretreat complex protein sample. Protein adsorption studies have shown that Nb₆O₁₉/MIL-125(Ti) can promote the selective adsorption of Cyt-C due to the synergistic effect of electrostatic and hydrogen-bond interactions. At pH=10.0 (Britton-Robinson buffer), the adsorption efficiency of 300 μL 100 μg·mL^-1 Cyt-C onto 1.0 mg Nb₆O₁₉/MIL-125(Ti) can reach 99.5%. The adsorption behavior of Cyt-C fits well with the Langmuir adsorption model, corresponding to a maximum theoretical adsorption capacity of 168.35 mg·g^-1. Using 3 mol·L^-1 NaCl as the eluent, a high elution efficiency of 92.19% is obtained. In addition, the results of the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis confirm that Nb₆O₁₉/MIL-125(Ti) efficiently adsorbed Cyt-C from scrofa heart extraction. LC-MS/MS spectrometry results show that the purification of Cyt-C reduces the abundance from the 12th to the 154th place after Nb₆O₁₉/MIL-125(Ti) treatment. Moreover, low abundant proteins, e.g., Superoxide dismutase 1, IF rod domain-containing protein and Ubiquitin-60S ribosomal protein L40 were considerably enriched. These outcomes confirm the practicability of Nb₆O₁₉/MIL-125 (Ti) as a Cyt-C extractant has potential application value in scrofa heart proteomics.

A point-to-point "cap" strategy to construct a highly selective dual-function molecularly-imprinted sensor for the simultaneous detection of HAV and HBV

As an artificial biomimetic receptor, molecularly-imprinted polymer (MIP) has been widely used for the separation, enrichment and detection of various substances. However, due to the complexity of virus structure, huge volume and the existence of highly similar viruses, MIP shows unsatisfactory selectivity in virus detection. To overcome these issues, two kinds of virus nanoMIPs, just like a "cap", were synthesized by a solid-phase imprinting nanogel technique. The "cap" had no inner core and was much smaller than that of a conventional MIP, which was more favorable for mass transfer. Moreover, each "cap" could only combine with one target virus, which avoided the interference between large-volume virus molecules effectively. The two synthesized "caps" were mixed to construct a bifunctional MIP virus sensor for the simultaneous detection of Hepatitis A virus (HAV) and Hepatitis B virus (HBV). As expected, the selectivity factor (SF) for HBV detection reached 13.7, which was much higher than the reported virus MIP sensors (SF: 3-6), which was comparable to that of small molecular imprinting sensors. In addition, the high sensitivity toward HBV was 34.3 fM, and that of HAV was 27.1 pM. This method provides an idea for preparing high-selectivity biomacro-MIPs, as well as a method for the simultaneous detection of similar viruses with high sensitivity and selectivity. The recovery experiment of spiked serum showed that this method also has great practical application prospects.

Cytochrome c in cancer therapy and prognosis

Cytochrome c (cyt c) is an electron transporter of the mitochondrial respiratory chain. Upon permeabilization of the mitochondrial outer membrane, cyt c is released into the cytoplasm, where it triggers the intrinsic pathway of apoptosis. Cytoplasmic cyt c can further reach the bloodstream. Apoptosis inhibition is one of the hallmarks of cancer and its induction in tumors is a widely used therapeutic approach. Apoptosis inhibition and induction correlate with decreased and increased serum levels of cyt c, respectively. The quantification of cyt c in the serum is useful in the monitoring of patient response to chemotherapy, with potential prognosis value. Several highly sensitive biosensors have been developed for the quantification of cyt c levels in human serum. Moreover, the delivery of exogenous cyt c to the cytoplasm of cancer cells is an effective approach for inducing their apoptosis. Similarly, several protein-based and nanoparticle-based systems have been developed for the therapeutic delivery of cyt c to cancer cells. As such, cyt c is a human protein with promising value in cancer prognosis and therapy. In addition, its thermal stability can be extended through PEGylation and ionic liquid storage. These processes could contribute to enhancing its therapeutic exploitation in clinical facilities with limited refrigeration conditions. Here, I discuss these research lines and how their timely conjunction can advance cancer therapy and prognosis.

Ring -opening of polythiolactones to construct protein-imprinted nanospheres with high recognition and regulation capabilities

Developing and preparing novel protein-imprinted nanomaterials with high recognition ability remains challenging because it is difficult to controllably and orderly design and arrange functional groups on the imprinted polymer layers of protein-imprinted nanomaterials to improve their protein identification. Herein, we present a new technology using rationally designed polythiolactone-decorated magnetic nanospheres as the precursor of multifunctionalized imprinted materials. Moreover, the strategy of ring-opening the polythiolactione layers using primary amines with terminal alcohols, acids and pyrrolidines introduces abundant recognition sites, which enhance the recognition for template proteins through multiple hydrogen-bonding and hydrophobic interactions. Thiols generated in situ by the ring-opening reaction provide sufficient crosslinking sites proximate to each recognition site for the formation of imprinting cavities, endowing the imprinted nanospheres with promising regulation capabilities. Based on the rational design, the imprinted nanospheres can be prepared conveniently and present tunable rebinding capacity and specificity for bovine serum albumin (BSA). The maximum saturated rebinding capacity of imprinted materials for BSA is up to 285 ± 15 mg g^-1 and the highest imprinting factor reaches 5.79. The simple and versatile strategy demonstrated in this study shows promise for the design of other protein-imprinted materials with high recognition ability.

Fabrication of efficient protein imprinted materials based on pearl necklace-like MOFs bacterial cellulose composites

The acquisition of efficient protein isolation substances is vital for proteomic research, whereas it's still challenging nowadays. Herein, an elaborately designed protein imprinted material based on a bacterial cellulose@ZIF-67 composite carrier (BC@ZIF-67) is proposed for the first time. In particular, due to the ultrafine fiber diameter and abundant hydroxyl functional groups of the bacterial cellulose, BC@ZIF-67 presented a compact arrangement structure similar to a pearl necklace, which greatly promoted template immobilization and mass transfer resistance in protein imprinting technology. Therefore, the protein-imprinted material (BC@ZIF-67@MIPs) fabricated by surface imprinting technology and template immobilization strategy could exhibit ultrahigh adsorption capacity (1017.0 mg g^-1), excellent recognition (IF = 5.98) and rapid adsorption equilibrium time (50 min). In addition, based on the experiment outcomes, our team employed BC@ZIF-67@MIPs to enrich template protein in blended protein solutions and biosamples, identifying them as underlying candidates for isolating and purifying proteins.

Recent advances in protein-imprinted polymers: synthesis, applications and challenges

The molecular imprinting technique (MIT), also described as the "lock to key" method, has been demonstrated as an effective tool for the creation of synthetic polymers with antibody-like sites to specifically recognize target molecules. To date, most successful molecular imprinting researches were limited to small molecules (<1500 Da); biomacromolecule (especially protein) imprinting remains a serious challenge due to their large size, chemical and structural complexity, and environmental instability. Nevertheless, protein imprinting has achieved some significant breakthroughs in imprinting methods and applications over the past decade. Some special protein-imprinted materials with outstanding properties have been developed and exhibited excellent potential in several advanced fields such as separation and purification, proteomics, biomarker detection, bioimaging and therapy. In this review, we critically and comprehensively surveyed the recent advances in protein imprinting, particularly emphasizing the significant progress in imprinting methods and highlighted applications. Finally, we summarize the major challenges remaining in protein imprinting and propose its development direction in the near future.

Constructing High-Recognition Protein-Imprinted Materials Using "Specially Designed" Block Macromolecular Chains as Functional Monomers and Crosslinkers

The use of a macromolecularly functional monomer and crosslinker (MFM) to stabilize and imprint a template protein is a new method to construct high-recognition protein-imprinted materials. In this study, for the first time, a "specially designed" block MFM with both "functional capability" and "crosslinking capability" segments was synthesized via reversible addition-fragmentation chain-transfer polymerization and used to fabricate bovine serum albumin (BSA)-imprinted microspheres (SiO₂@MPS@MIPs-MFM) by the surface imprinting strategy. Results from circular dichroic spectrum experiments reflected that the block MFM could maintain the natural form of BSA, whereas its corresponding and equivalent micromolecularly functional monomer (MIM) seriously destroyed the secondary structure of proteins. Batch rebinding experiments showed that the maximum adsorption capacity and imprinting factor of SiO₂@MPS@MIPs-MFM reached 314.9 mg g^-1 and 4.02, which were significantly superior to that of MIM-based imprinted materials. In addition, since the crosslinking capability segments in block MFM involved zwitterionic functional groups with a protein-repelling effect, SiO₂@MPS@MIPs-MFM showed better specific rebinding ability than the imprinted material prepared by MFM without this component. Besides, scanning electron microscopy and transmission electron microscopy images showed that the shell thickness of SiO₂@MPS@MIPs-MFM was approximately 15 nm, and such a thin imprinted layer ensured its rapid adsorption equilibrium (120 min). As a result, SiO₂@MPS@MIPs-MFM revealed fantastic selectivity and recognition ability in a mixed protein solution and could efficiently extract BSA from biological samples of bovine calf serum. The proposal of block MFM enriched the options and designability of monomers in protein imprinting technology, thereby laying a foundation for developing high-performance protein-imprinted materials.