Glycocyamine functionalized magnetic layered double hydroxides with multiple affinity sites for trace phosphopeptides enrichment

Enrichment of phosphopeptides by arginine-functionalized magnetic chitosan nanoparticles

One of the most crucial and prevalent post-translational modifications is the phosphorylation of proteins. The study and examination of protein phosphorylation hold immense importance in comprehending disease mechanisms and discovering novel biomarkers. However, the inherent low abundance, low ionization efficiency, and coexistence with non phosphopeptides seriously affect the direct analysis of phosphopeptides by mass spectrometry. In order to tackle these problems, it is necessary to carry out selective enrichment of phosphopeptides prior to conducting mass spectrometry analysis. Herein, magnetic chitosan nanoparticles were developed by incorporating arginine, and were then utilized for phosphopeptide enrichment. A tryptic digest of β-casein was chosen as the standard substance. After enrichment, combined with matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS), the detection limit of the method was 0.4 fmol. The synthesized magnetic material demonstrated great potential in the detection of phosphopeptides in complex samples, as proven by its successful application in detecting phosphopeptides in skim milk and human saliva samples.

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

A guanidine-functionalized (GF) covalent organic framework (COF) nanocomposite has been developed by a post-synthetic approach for specific capture and separation of phosphopeptides and exosomes. The abundant binding sites on COF can immobilize a large number of gold nanoparticles (AuNPs), which can be used to react with amino groups to graft polyethyleneimine (PEI). Finally, Fe₃O₄@COF@Au@PEI-GF is obtained through the reaction of PEI and guanidyl group for phosphopeptides and exosomes detection. This composite shows a low detection limit (0.02 fmol), size exclusion effect (β-casein digests:Albumin from bovine serum protein = 1:10,000), good reusability (10 cycles), and high selectivity (β-casein digests:Albumin from bovine serum digests = 1:10,000). For complex biological sample, 4 phosphopeptides can be successfully identified from human serum. Furthermore, for the first time, we used guanidyl-functionalized probe to capture exosomes in human serum, providing a new method for enriching exosomes. The above experiments showed that Fe₃O₄@COF@Au@PEI-GF not only effectively enrich phosphopeptides and remove macromolecular proteins, but also successfully separate and capture exosomes. This demonstrates the great potential of this composite for the specific enrichment of phosphopeptides and isolation of exosomes.

Metal-organic framework-mediated synthesis of hierarchical layered double hydroxide for high-efficiency enrichment of phosphopeptides

When applied as adsorbents for phosphopeptides enrichment, two-dimensional (2D) layered double hydroxides (LDHs) are usually limited by the disadvantages of buried affinity sites and reduced specific surface area. Multifarious exfoliation strategies have been implemented to compensate for these deficiencies, but tedious exfoliation process cannot meet the requirements of LDHs as high-efficiency adsorbents. Incorporating LDHs with three-dimensional (3D) template can avoid tedious exfoliation and produce hierarchical LDHs with large specific surface area and massive affinity sites. Herein, a hierarchical LDH (denoted as Fe₃O₄@ZIF-8@Zn-Ga LDH) was prepared by metal-organic framework (MOF)-mediated synthesis strategy, and a magnetic solid-phase extraction (MSPE) platform was constructed and employed for phosphopeptides enrichment with high efficiency. The unique 3D structure and abundant metal nodes of MOF provide 3D template and metal sources for in-situ nucleation and generation of LDH. Large specific surface area and massive exposed Zn and Ga endow Fe₃O₄@ZIF-8@Zn-Ga LDH with high enrichment efficiency toward phosphopeptides from complicated biological samples. With the aid of mass spectrometry (MS) techniques, we profiled endogenous or global phosphopeptides from human saliva and serum, which proved the practical application value of this material.

Quantum confined peptide assemblies in a visual photoluminescent hydrogel platform and smartphone-assisted sample-to-answer analyzer for detecting trace pyrethroids

Quantum confinement (QC) effect-related materials have been extensively studied as photoluminescent probes for agricultural, food, and environmental analyses, with the advantage of simple-to-synthesize, reusable, nontoxic, and environmentally friendly. Herein, we propose a strategy to dimerize aromatic cyclo-dipeptides, namely cyclo-ditryptophan (cyclo-WW), cyclo-diphenylalanine (cyclo-FF), and cyclo-dihistidine (cyclo-HH), into quantum dots as basic building blocks for the self-assembly of QC supramolecular structures with excellent photoluminescent properties in aqueous solutions. In particular, through coordination with Zn(II), the bandgap can be tuned to change the photo-absorption and luminescence properties of the cyclo-dipeptide-based QC assemblies. The fluorescence quantum yield of cyclo-WW+Zn(II) was 16.9%. Such a good luminous effect makes it applicable to the detection of LC. A good linear relationship between fluorescence response of cyclo-WW+Zn(II) and LC concentration was observed in the range of 5-350 μg/L, with a low limit of detection of 2.9 μg/L and good spiked recovery of 90.72%-104.3%. A visual platform using the cyclo-WW+Zn(II)-based photoluminescent hydrogel and smartphone-assisted sample-to-answer analyzer were developed, which showed good responsiveness to LC. The developed fluorescence method, validated using traditional HPLC, is a biocompatible alternative for the rapid detection of trace pollutants with the advantages of portability and simple operation.

Layer-by-layer assembly of multilayered double hydroxides/polyoxometalate-coated magnetic nanoparticles for highly efficient phosphopeptide enrichment

A layer-by-layer (LbL) assembly strategy was developed to prepare multilayered double hydroxide/polyoxometalate shell-coated magnetic nanoparticles. The introduction of functional shells not only offered abundant affinity sites of metal oxide and metal ions but also increased the surface area for the contact with targets. By combining the enrichment strategies of immobilized metal ion affinity chromatography and metal oxide affinity chromatography, the nanomaterial can capture phosphopeptides via a synergistic effect. The method presented a low detection limit of 0.1 fmol in combination with matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis. The nanomaterial showed satisfactory selectivity (1:1:5000 M ratio of α-/β-casein/bovine serum albumin), good recovery (92.07%), high adsorption capacity (117.6 mg g^-1), and ten times reusability for capturing phosphopeptides.

Nanostructure stable hydrophilic hierarchical porous metal-organic frameworks for highly efficient enrichment of glycopeptides

Protein glycosylation plays a vital role in many physiological activities in organisms. Due to the low abundance of glycopeptides and the interference of numerous non-glycopeptides in biological samples, selective enrichment of glycopeptides is of great significance for their successful identification. Metal organic frameworks (MOFs) materials are appropriate for glycopeptides enrichment by virtue of their large specific surface area and outstanding hydrophilic properties. However, the instability of hydrophilic MOFs in acidic solutions have severely limited their applications. In this work, a rational facile strategy was established to synthesize a stable hydrophilic hierarchical porous MOF (denoted as HP-MOF-Arg@mSiO₂). This new material improved the selectivity and sensitivity of enrichment for glycopeptides via modification of arginine groups. More importantly, the mesoporous silica layer was introduced to enhance the stability of MOFs in aqueous solution and achieve the size exclusion effect of large-size proteins in complex samples. Overall, owing to the unique hierarchical porous and the hydrophilic modification, the synthesized HP-MOF-Arg@mSiO₂ materials showed excellent hydrophilicity and hydrolytic stability, resulting in outstanding specific separation capacity in glycopeptides enrichment. A total of 521 and 342 glycopeptides were respectively captured from 2 μL human serum digests and mouse testis tissue digests, revealing the potential of the materials in the study of glycoproteomics in complex biological samples.

Magnetic solid-phase extraction of high molecular weight peptides using stearic acid-functionalized magnetic hydroxyapatite nanocomposite: determination of some hypothalamic agents in biological samples

Therapeutic peptides have an important effect on physiological function and human health, so it is momentous to quantify and detect low levels of these biomolecules in biological samples for treatment and diagnostic purposes. In the present study, an efficient magnetic solid-phase extraction (MSPE) method was developed based on stearic acid-functionalized magnetic hydroxyapatite nanocomposite (MHAP/SA) as a novel and cost-effective adsorbent for extraction of five hypothalamic-related peptides (goserelin, octreotide, triptorelin, somatostatin, and cetrorelix) from biological samples. To characterize the morphology and physicochemical properties of MHAP/SA, Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDS), field emission scanning microscopy (FE-SEM), CHNS elemental analysis, Brunauer-Emmett-Teller (BET), and vibrating sample magnetometry (VSM) were applied. Under optimum conditions, the proposed method (MSPE-HPLC-UV) represented favorable linearity with R² ≥ 0.9987, suitable intra- and inter-day precisions (RSD ≤ 6.9% and RSD ≤ 8.1%, respectively, n = 3), and limits of detection and quantification in the range of 0.75-1.12 ng mL^-1 and 2.50-3.75 ng mL^-1, respectively. Eventually, the proposed method was used for the extraction and quantification of target therapeutic peptides in plasma and urine samples, and satisfactory relative recoveries were achieved in the range of 90.6-110.3%.

Comparative evaluation of MAX-Ti3AlC2 and MXene-Ti3C2 as affinity chromatographic materials for highly selective enrichment of phosphopeptides

MAX and MXene have received considerable attention owing to their outstanding performance in fields like battery and catalysis. However, their possible biomedical applications have rarely been considered, especially the affinity chromatographic applications in proteomics. In this work, considering the large number of exposed metal sites, small binding potential resistance and fast mass transfer speed, layered ternary carbides MAX-Ti₃AlC₂ and MXene-Ti₃C₂ with a two-dimensional nanostructure were successfully explored for the first time as affinity chromatography stationary phases for the specific capture of phosphopeptides from complex biological samples. Helium ion microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction spectra, X-ray photoelectron spectroscopy and zeta potential measurement results confirmed that the MXene-Ti₃C₂ was well exfoliated from the pristine MAX-Ti₃AlC₂. Ti₃AlC₂ showed better enrichment specificity than MXene-Ti₃C₂. The detection limit of Ti₃AlC₂ was as low as 5 fmol. Even when the molar ratio of BSA to β-casein tryptic digests increased to 1000 : 1, two characteristic phosphopeptides with a relatively clear background could be detected after enrichment. After five cycles of repeated use, the enrichment specificity of Ti₃AlC₂ still remains. Furthermore, 91 and 830 unique phosphopeptides from 23 and 525 phosphoproteins were identified from milk and BEL7402 cells, respectively. Among them, 27 and 170 phosphopeptides, 12 and 56 phosphoproteins identified from milk and BEL7402 cells were not detected with commercial TiO₂ after three independent replicates, which have great potential in providing complementary coverage of phosphoproteome. This work opens up new applications of Ti₃AlC₂ and MXene-Ti₃C₂, and will play more important role for phosphorylated proteomics in biomedicine.