Magnetic guanidyl-functionalized covalent organic framework composite: a platform for specific capture and isolation of phosphopeptides and exosomes

Preparation of a titanium-functionalized polymeric material rich in hydrophilic groups for phosphoproteome and glycoproteome analyses in serum

The analysis of protein phosphorylation and glycosylation is critical for investigating disease development. In this work, 1,2-epoxy-5-hexene and N,N-methylenebisacrylamide were polymerized with vinyl phosphate to produce a polymer (denoted as PVME), which contained a variety of hydrophilic groups. The material's hydrophilicity was further enhanced by a ring-opening reaction with cysteine (the product was denoted as Cys-PVEM). Finally, titanium sulfate was combined with Cys-PVME to form titanium-rich polymers (Cys-PVME-Ti4+) for the enrichment of phosphopeptides and glycopeptides. Cys-PVME-Ti4+ has a good sensitivity (0.02 fmol) and selectivity (1 : 1000) with a loading capacity of 62 mg g-1, recyclability (9 cycles), and a good recovery rate (101.6 ± 0.60%) for phosphopeptides, and good sensitivity (0.01 fmol μL-1), selectivity (1 : 2000), a loading capacity of 62.5 mg g-1, recyclability (9 cycles), and a good recovery rate (98.7 ± 1.2%) for glycopeptides. In addition, after enrichment with this material, 27 phosphopeptides with 14 phosphoproteins and 223 glycopeptides associated with 88 glycoproteins were captured from the serum of colorectal cancer patients, while 27 phosphopeptides associated with 14 phosphoproteins and 210 glycopeptides associated with 111 glycoproteins were also captured from the serum of a normal control. Gene ontology (GO) analysis revealed that complement activation, extracellular region, extracellular space, blood coagulation, the IgG immunoglobulin complex, and heparin binding were different between normal control and colorectal cancer, implying that related pathways are likely involved in colorectal cancer pathogenesis.

Core-shell structures assembled from magnetic covalent organic frameworks as a Ti4+-fixed affinity substrate for the identification of phosphopeptides in colorectal cancer serum

When it comes to the early detection of colorectal cancer (CRC), the study of protein phosphorylation is crucial. This work used magnetic covalent organic framework (COF) materials as substrates. The magCOF@PM-Ti4+ composites were obtained by constructing the three-dimensional cross-linked structures and chelating them with Ti4+ in a green and economical way, which was utilized to identify the phosphopeptides. This material possesses magnetic properties that facilitate simplified experimental manipulation, has superior sensitivity (0.2 fmol), excellent selectivity (1000:1), and good reusability (10 cycles), and achieves outstanding recovery rates (103.4 ± 1.2%). In addition, magCOF@PM-Ti4+ was utilized to identify phosphopeptides in human serum. One hundred phosphopeptides were identified from three normal control serums, whereas 98 phosphopeptides were identified from three CRC serums. The results demonstrated that magCOF@PM-Ti4+ has great potential in efficiently identifying low-abundance phosphopeptides.

Exploitation of porphyrin-based titanium-rich porous organic polymers for targeted phosphopeptide enrichment from the serum of colorectal cancer individuals

A porphyrin-based titanium-rich porous organic polymer (Th-PPOPs@Ti4+) was designed based on immobilized metal ion affinity chromatography technique and successfully applied to phosphopeptide enrichment with 5,10,15,20-tetrakis(4-carboxyphenyl) porphine tetramethyl ester (TCPTE), 2,3-dihydroxyterephthalaldehyde (DHTA), and 2,3,4-trihydroxybenzaldehyde (THBA) as raw materials. Th-PPOPs@Ti4+ exhibited remarkable sensitivity (0.5 fmol), high selectivity (β-casein: BSA = 1:2000, molar ratio), outstanding recovery (95.0 ± 1.9%), reusability (10 times), and superior loading capacity (143 mg·g-1). In addition, Th-PPOPs@Ti4+ exhibited excellent ability to specifically capture phosphopeptides from the serum of colorectal cancer (CRC) individuals and normal subjects. Sixty phosphopeptides assigned to 35 phosphoproteins were obtained from the serum of CRC individuals, and 43 phosphopeptides allocated to 28 phosphoproteins were extracted in the serum of healthy individuals via nano-LC-MS/MS. Gene ontology assays revealed that the detected phosphoproteins may be inextricably tied to CRC-associated events, including response to estrogen, inflammatory response, and heparin binding, suggesting that it is possible that these correlative pathways may be implicated in the pathogenesis of CRC.

Progress in Core-Shell Magnetic Mesoporous Materials for Enriching Post-Translationally Modified Peptides

Endogenous peptides, particularly those with post-translational modifications, are increasingly being studied as biomarkers for diagnosing various diseases. However, they are weakly ionizable, have a low abundance in biological samples, and may be interfered with by high levels of proteins, peptides, and other macromolecular impurities, resulting in a high limit of detection and insufficient amounts of post-translationally modified peptides in real biological samples to be examined. Therefore, separation and enrichment are necessary before analyzing these biomarkers using mass spectrometry. Mesoporous materials have regular adjustable pores that can eliminate large proteins and impurities, and their large specific surface area can bind more target peptides, but this may result in the partial loss or destruction of target peptides during centrifugal separation. On the other hand, magnetic mesoporous materials can be used to separate the target using an external magnetic field, which improves the separation efficiency and yield. Core-shell magnetic mesoporous materials are widely utilized for peptide separation and enrichment due to their biocompatibility, efficient enrichment capability, and excellent recoverability. This paper provides a review of the latest progress in core-shell magnetic mesoporous materials for enriching glycopeptides and phosphopeptides and compares their enrichment performance with different types of functionalization methods.

An amino-rich polymer-coated magnetic nanomaterial for ultra-rapid separation of phosphorylated peptides in the serum of Parkinson's disease patients

The elucidation of disease pathogenesis can be achieved by analyzing the low-abundance phosphopeptides in organisms. Herein, we developed a novel and easy-to-prepare polymer-coated nanomaterial. By improving the hydrophilicity and spatial conformation of the material, we effectively enhanced the adsorption of phosphopeptides and demonstrated excellent enrichment properties. The material was able to successfully enrich the phosphopeptides in only 1 min. Meanwhile, the material has high selectivity (1:2000), good loading capacity (100 μg/mg), excellent sensitivity (0.5 fmol), and great acid and alkali resistance. In addition, the material was applied to real samples, and 70 phosphopeptides were enriched from the serum of Parkinson's disease (PD) patients and 67 phosphopeptides were enriched from the serum of normal controls. Sequences Logo showed that PD is probably associated with threonine, glutamate, serine, and glutamine. Finally, gene ontology (GO) analysis was performed on phosphopeptides enriched in PD patients' serum. The results showed that PD patients expressed abnormal expression of the cholesterol metabolic process and cell-matrix adhesion in the biological process (BP), endoplasmic reticulum and lipoprotein in the cellular component (CC), and heparin-binding, lipid-binding, and receptor-binding in the molecular function (MF) as compared with normal individuals. All the experiments indicate that the nanomaterials have great potential in proteomics studies.

Increasing the sensitivity and accuracy of detecting exosomes as biomarkers for cancer monitoring using optical nanobiosensors

The advancement of nanoscience and material design in recent times has facilitated the creation of point-of-care devices for cancer diagnosis and biomolecule sensing. Exosomes (EXOs) facilitate the transfer of bioactive molecules between cancer cells and diverse cells in the local and distant microenvironments, thereby contributing to cancer progression and metastasis. Specifically, EXOs derived from cancer are likely to function as biomarkers for early cancer detection due to the genetic or signaling alterations they transport as payload within the cancer cells of origin. It has been verified that EXOs circulate steadily in bodily secretions and contain a variety of information that indicates the progression of the tumor. However, acquiring molecular information and interactions regarding EXOs has presented significant technical challenges due to their nanoscale nature and high heterogeneity. Colorimetry, surface plasmon resonance (SPR), fluorescence, and Raman scattering are examples of optical techniques utilized to quantify cancer exosomal biomarkers, including lipids, proteins, RNA, and DNA. Many optically active nanoparticles (NPs), predominantly carbon-based, inorganic, organic, and composite-based nanomaterials, have been employed in biosensing technology. The exceptional physical properties exhibited by nanomaterials, including carbon NPs, noble metal NPs, and magnetic NPs, have facilitated significant progress in the development of optical nanobiosensors intended for the detection of EXOs originating from tumors. Following a summary of the biogenesis, biological functions, and biomarker value of known EXOs, this article provides an update on the detection methodologies currently under investigation. In conclusion, we propose some potential enhancements to optical biosensors utilized in detecting EXO, utilizing various NP materials such as silicon NPs, graphene oxide (GO), metal NPs, and quantum dots (QDs).

Enrichment of Phosphopeptides Based on Zirconium Phthalocyanine-Modified Magnetic Nanoparticles

Highly selective extraction of phosphopeptides is necessary before mass spectrometry (MS) analysis. Herein, zirconium phthalocyanine-modified magnetic nanoparticles were prepared through a simple method. The Fe-O groups on Fe3O4 and the zirconium ions on phthalocyanine had a strong affinity for phosphopeptides based on immobilized metal ion affinity chromatography (IMAC). The enrichment platform exhibited low detection limit (0.01 fmol), high selectivity (α-/β-casein/bovine serum albumin, 1/1/5000), good reusability (10 circles), and recovery (91.1 ± 1.1%) toward phosphopeptides. Nonfat milk, human serum, saliva, and A549 cell lysate were employed as actual samples to assess the applicability of the enrichment protocol. Metallo-phthalocyanine will be a competitive compound for designing highly efficient adsorbents and offers a new approach to phosphopeptide analysis.

Facile synthesis of Fe3+ immobilized magnetic polydopamine-polyethyleneimine composites for phosphopeptide enrichment

As one of the most common post-translational modification of proteins, protein phosphorylation plays a vital role in many physiological processes. The enrichment of phosphopeptides is highly important before the mass spectrometry detection since phosphopeptides are susceptible to interferences from high-abundance non-phosphopeptides. In this study, we designed a novel magnetic composite (Fe3O4@PDA-PEI-Fe3+) for phosphopeptide enrichment with a facile protocol. The developed Fe3O4@PDA-PEI-Fe3+ is a marvelous material with multiple functional groups, and can effectively enrich phosphopeptides through the synergistic effect of three mechanisms, i.e., immobilized metal ion affinity chromatography raised form Fe3+, electrostatic interaction between amine and phosphate groups, and hydrogen bond between the hydrogen atoms of amine groups and oxygen atoms of phosphate groups. Combined with mass spectrometry, the material shows excellent enrichment performance, high sensitivity (0.4 fmol), good selectivity (β-casein:BSA= 1:500, w:w), and stable reusability (at least 5 cycles). In addition, the material was successfully applied to enrich phosphopeptides from skim milk and human saliva samples, implying that it is an ideal adsorbent for the phosphopeptide enrichment in complex biological samples and provides valuable insights into the field of phosphopeptide analysis.

Combination of click chemistry and Schiff base reaction: Post-synthesis of covalent organic frameworks as an immobilized metal ion affinity chromatography platform for efficient capture of global phosphopeptides in serum with chronic obstructive pulmonary disease

Reasonable design and construction of functionalized materials are of great importance for the enrichment of global phosphopeptides. In this work, Ti4+ functionalized hydrophilic covalent organic frameworks by introducing glutathione (GSH) and 2,3,4-trihydroxy benzaldehyde (THBA) via click chemistry and Schiff base reaction (COF-V@GSH-THBA-Ti4+ ) was constructed and applied for selective enrichment of phosphopeptides in serum. Benefit from the high surface area, excellent hydrophilicity as well as regular mesoporous structure, COF-V@GSH-THBA-Ti4+ displayed high selectivity (molar ratio of 2000:1), low limit of detection (0.5 fmol), high load capacity (100.0 mg/g) and excellent size-exclusion effect (1:10000) for enrichment of phosphopeptides. For actual bio-sample analysis, 15 phosphopeptides assigned to 10 phosphoproteins with 16 phosphorylated sites and 33 phosphopeptides assigned to 25 phosphoproteins with 34 phosphorylated sites were detected from the serum of patients with chronic obstructive pulmonary disease (COPD), and normal controls. Biological processes and molecular functions analysis further disclosed the difference of serums with phosphoproteomics between COPD and normal controls.

A novel carbon-based material with titanium and zirconium ions etched on hollow mesoporous carbon tubes for specific capture of phosphopeptides and exosomes

The analysis of low abundance phosphopeptides in organisms and specific capture exosomes are crucial for unraveling the pathogenesis of diseases. For this reason, titanium-zirconium ions and highly biocompatible dopamine and polyimide tubes (PITs) were introduced, and a novel carbon-based material with titanium and zirconium ions etched on hollow mesoporous carbon tubes (HMCT), denoted as G@C@Ti-Zr-HMCT, comes into being after high-temperature calcination. Attributing to the tightly bound titanium and zirconium ions to HMCT and the high carbon content of the polydopamine carbonaceous layer, G@C@Ti-Zr-HMCT displays satisfactory capability of enriching phosphopeptides with satisfactory detection limit (0.2 fmol), extraordinary selectivity (1:2000), and good loading capacity (100 μg/mg). In addition, 25 phosphopeptides related to 25 phosphoproteins from the serum of Parkinson's disease (PD) patients and 30 phosphopeptides attributed to 26 phosphoproteins from the serum of healthy individuals were enriched by G@C@Ti-Zr-HMCT, respectively. In addition, bioinformatics analysis of the above results revealed that PD were associated with serine, threonine, and leucine of high frequency, blood coagulation in BP, Golgi apparatus and mitochondrial outer membrane in CC, and heparin binding in MF. Moreover, the phospholipid bilayer of exosomes and metallic titanium and zirconium ions interact to produce the following results: this highly biocompatible carbon-based material was successfully applied to capture exosomes, which offers a promising platform for isolating exosomes. To sum up, these delightful results confirmed without doubt that G@C@Ti-Zr-HMCT has enjoyed a splendiferous future in the specific capture of phosphopeptides and exosomes isolation.

In situ grown magnetic COF@MOF with a phosphoserine anchor for in-depth N-glycopeptide analysis in serum

A hydrophilic phosphoserine-functionalized magnetic organic framework composite (termed Fe3O4@COF@MOF-PS) was synthesized by an in situ growth strategy for effective capture of N-glycopeptides. Fe3O4@COF@MOF-PS exhibited high sensitivity (0.2 fmol μL-1), outstanding exclusion of size capability (1 : 10 000), good selectivity (1 : 2000), and reusability (at least 10 times). It also exhibited remarkable performance in the N-glycopeptide analysis in complex biological samples. Via nano-LC-MS/MS analysis, a total of 223 N-glycopeptides with 161 glycosylation sites assigned to 91 glycoproteins and 331 N-glycopeptides with 243 glycosylation sites assigned to 134 glycoproteins were identified in sera from cervical cancer patients and normal controls, respectively. Biological processes and molecular functional analyses indicate that the captured glycoproteins are of significant relevance to cervical cancer, for example, gene coverage or expression of cell adhesion and extracellular matrix structural constituents. Thus, Fe3O4@COF@MOF-PS not only efficiently captures N-glycopeptides, but also has the possibility of screening potential disease markers and elucidating the process of cervical cancer development.

Post-synthesis of a titanium-rich magnetic COF nanocomposite with flexible branched polymers for efficient enrichment of phosphopeptides from human saliva and serum

A Ti4+-functionalized magnetic covalent organic framework material with flexible branched polymers (mCOF@ε-PL@THBA-Ti4+) built via an immobilized metal ion affinity chromatography (IMAC) enrichment strategy was proposed through post-synthesis modification. Hydrophilic ε-poly-L-lysine (ε-PL) rich in amino active groups was first introduced in the fabrication of the phosphopeptide enrichment material to increase the hydrophilicity while providing more functional modification pathways of the material. 2,3,4-Trihydroxy-benzaldehyde (THBA) provides abundant binding sites for the immobilization of numerous Ti4+, which is advantageous for the subsequent efficient phosphopeptide enrichment. The magnetic nanocomposite exhibited outstanding performance of phosphopeptide enrichment with good selectivity (1 : 5000), a low detection limit (2 fmol), and relatively high loading capacity (66.7 mg g-1). What's more, after treatment with mCOF@ε-PL@THBA-Ti4+, 16 endogenous phosphopeptides from fresh saliva of healthy people were recognized by MALDI-TOF MS, and 50 phosphopeptides belonging to 35 phosphoproteins from the serum of uremia patients were detected by nano-LC-MS/MS. Proteomics data analysis for the differential protein selection between uremia and normal controls was conducted using R software, and four down-regulated and three up-regulated proteins were obtained. The results suggested that the prepared material has potential applications in biomarker discovery.

Ti4+ functionalized β-cyclodextrin covalent organic framework as a new immobilized metal ion affinity chromatography platform for selective capture of phosphorylated peptides and exosomes

A Ti4+ functionalized β-cyclodextrin covalent organic framework nanoparticle (named as β-CD-COF@Ti4+) was synthesized using a one-pot method successfully realizing the enrichment of phosphorylated peptides and exosomes based on the immobilized metal ion affinity chromatography strategy. The functionalized β-CD-COF@Ti4+ exhibited superior performance on the enrichment of phosphopeptides, including high selectivity (1:1000), low detection limit (0.5 fmol), and loading capacity for phosphopeptides (100 mg·g-1). After treatment with β-CD-COF@Ti4+, 9 phosphopeptides from defatted milk, 29 phosphopeptides related to 23 phosphoproteins from normal group serum, and 24 phosphopeptides related to 22 phosphoproteins from the serum of uremia patients were captured. Through the analysis of Gene Ontology, the captured phosphoprotein is closely related to kidney disease, including lipoprotein metabolism, very-low-density lipoprotein particle, high-density lipoprotein particle, and lipid binding activity process. Furthermore, western blot verification showed that this nanoparticle could successfully capture exosomes from human serum. This study demonstrates great prospects for the enrichment of phosphopeptides and exosomes from actual bio-samples.

Biogenesis, Isolation, and Detection of Exosomes and Their Potential in Therapeutics and Diagnostics

The increasing research and rapid developments in the field of exosomes provide insights into their role and significance in human health. Exosomes derived from various sources, such as mesenchymal stem cells, cardiac cells, and tumor cells, to name a few, can be potential therapeutic agents for the treatment of diseases and could also serve as biomarkers for the early detection of diseases. Cellular components of exosomes, several proteins, lipids, and miRNAs hold promise as novel biomarkers for the detection of various diseases. The structure of exosomes enables them as drug delivery vehicles. Since exosomes exhibit potential therapeutic applications, their efficient isolation from complex biological/clinical samples and precise real-time analysis becomes significant. With the advent of microfluidics, nano-biosensors are being designed to capture exosomes efficiently and rapidly. Herein, we have summarized the history, biogenesis, characteristics, functions, and applications of exosomes, along with the isolation, detection, and quantification techniques. The implications of surface modifications to enhance specificity have been outlined. The review also sheds light on the engineered nanoplatforms being developed for exosome detection and capture.