Facile "one-pot" preparation of phosphonate functional polythiophene based microsphere via Friedel-Crafts reaction for selective enrichment of phosphopeptides from milk

Advanced functional materials as reliable tools for capturing food-derived peptides to optimize the peptidomics pre-treatment enrichment workflow

Peptidomics strategies with high throughput, sensitivity, and reproducibility are key tools for comprehensively analyzing peptide composition and potential functional activities in foods. Nevertheless, complex signal interference, limited ionization efficiency, and low abundance have impeded food-derived peptides' progress in food detection and analysis. As a result, novel functional materials have been born at the right moment that could eliminate interference and perform efficient enrichment. Of note, few studies have focused on developing peptide enrichment materials for food sample analysis. This work summarizes the development of endogenous peptide, phosphopeptide, and glycopeptide enrichment utilizing materials that have been employed extensively recently: organic framework materials, carbon-based nanomaterials, bio-based materials, magnetic materials, and molecularly imprinted polymers. It focuses on the limitations, potential solutions, and future prospects for application in food peptidomics of various advanced functional materials. The size-exclusion effect of adjustable aperture and the modification of magnetic material enhanced the sensitivity and selectivity of endogenous peptide enrichment and aided in streamlining the enrichment process and cutting down on enrichment time. Not only that, the immobilization of metal ions such as Ti4+ and Nb5+ enhanced the capture of phosphopeptides, and the introduction of hydrophilic groups such as arginine, L-cysteine, and glutathione into bio-based materials effectively optimized the hydrophilic enrichment of glycopeptides. Although a portion of the carefully constructed functional materials currently only exhibit promising applications in the field of peptide enrichment for analytical chemistry, there is reason to believe that they will further advance the field of food peptidomics through improved pre-treatment steps.

Preparation of high-efficiency titanium ion immobilized magnetic graphite nitride nanocomposite for phosphopeptide enrichment

BACKGROUND

Protein phosphorylation has been implicated in life processes including molecular interaction, protein structure transformation, and malignant disease. An in-depth study of protein phosphorylation may provide vital information for the discovery of early biomarkers. Mass spectrometry (MS)-based techniques have become an important method for phosphopeptide identification. Nevertheless, direct detection remains challenging because of the low ionization efficiency of phosphopeptides and serious interference from non-phosphopeptides. There is a great need for an efficient enrichment strategy to analyze protein phosphorylation prior to MS analysis.

RESULTS

In this study, a novel nanocomposite was prepared by introducing titanium ions into two-dimensional magnetic graphite nitride. The nanocomposite was combined with immobilized metal ion affinity chromatography (IMAC) and anion-exchange chromatography mechanisms for phosphoproteome research. The nanocomposite had the advantages of a large specific surface (412.9 m2 g-1), positive electricity (175.44 mV), and excellent magnetic property (35.7 emu g-1). Moreover, it presented satisfactory selectivity (α-casein:β-casein:bovine serum albumin = 1:1:5000), a low detection limit (0.02 fmol), great recyclability (10 cycles), and high recovery (92.8%). The nanocomposite demonstrated great practicability for phosphopeptides from non-fat milk, human serum, and saliva. Further, the nanocomposite was applied to enrich phosphopeptides from a more complicated specimen, A549 cell lysate. A total of 890 phosphopeptides mapping to 564 phosphoproteins were successfully detected with nano LC-MS.

SIGNIFICANCE

We successfully designed and developed an efficient analysis platform for phosphopeptides, which includes protein digestion, phosphopeptide enrichment, and MS detection. The MS-based enrichment platform was further used to analyze phosphopeptides from complicated bio-samples. This work paves the way for the design and preparation of graphite nitride-based IMAC materials for phosphoproteome analysis.

Cerium ions immobilized magnetic graphite nitride decorated with L-Alanyl-L-Glutamine as new chelator for enrichment of phosphopeptides

Cerium ions immobilized magnetic graphite nitride material have been prepared using L-Alanyl-L-Glutamine as the new chelator. The resulting Fe3O4/g-C3N4-L-Ala-L-Gln-Ce4+, as an immobilized metal ion affinity chromatography (IMAC) sorbent, was reusable. This is due to the strong coordination interaction between L-Alanyl-L-Glutamine and cerium ions. After a series of characterizations, the magnetic nanocomposite showed high surface area, good hydrophilicity, positive electricity, and magnetic response. Fe3O4/g-C3N4-L-Ala-L-Gln-Ce4+ had high sensitivity (0.1 fmol), selectivity (α-/β-casein/bovine serum albumin, 1:1:5000), and good recyclability (10 cycles). A total of 647 unique phosphopeptides mapped to 491 phosphoproteins were identified from A549 cell lysate by nano LC-MS analysis.

Polymer brush grafted immobilized metal ion affinity adsorbent based on polydopamine/polyethyleneimine-coated magnetic graphene oxide for selective enrichment of cytokinins in plants

An immobilized metal affinity (IMAC) adsorbent was prepared for selective enrichment of adenine type CKs, via grafting polymer chain pendant with iminodiacetic acid (IDA) from polydopamine (PDA)/polyethyleneimine (PEI)-coated magnetic graphene oxide (magGO) via surface-initiated-atom transfer radical polymerization (SI-ATRP). The prepared IMAC sorbent exhibited remarkable adsorption performances and good selectivity for adenine-type CKs and was utilized as a sorbent of magnetic solid-phase extraction (MSPE) for effective enrichment of four adenine-type CKs in bean sprouts. Under the optimized extraction conditions, an analytical method for four adenine type CKs in bean sprouts was established by combining the MSPE combined with ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The recoveries of the analytes were between 80.4 ± 1.9% and 114.6 ± 1.5% (n = 3). The limits of detection (LODs) range from 0.63 to 2.30 pg⋅mL^-1. The relative standard deviations of intra-day and inter-day were less than 12.6%. The established method was successfully applied to the selective extraction and sensitive detection of trace adenine-type CKs in plant samples.

Monodisperse Ti4+-immobilized macroporous adsorbent resins with polymer brush for improved multi-phosphopeptides enrichment in milk

Enrichment of phosphopeptides before mass spectrometry (MS) analysis is essential due to the limitations of low abundance and poor ionization efficiency in complex biological samples. Immobilized metal affinity chromatography (IMAC), especially titanium ion (Ti⁴⁺)-IMAC, has become a popular strategy for enrichment of phosphopeptides due to high selectivity and sensitivity. Conventional Ti⁴⁺-immobilized macroporous adsorption resin (MAR) fabricated by monolayer modification can preferentially capture mono-phosphopeptide over multi-phosphopeptides, which takes on more functions in the regulation of cell behaviors of organism. In this paper, a kind of monodisperse MAR microsphere with functional polymer brush (Ti⁴⁺-Brush@MAR) was prepared and modified via surface-initiated atom transfer radical polymerization (SI-ATRP). Compared with common Ti⁴⁺-MAR without polymer brush, Ti⁴⁺-Brush@MAR exhibited high enrichment specificity not only for mono-phosphopeptides but also for multi-phosphopeptides in β-casein or milk digest samples. As a result, a total of 93 unique phosphopeptides mapped to 18 phosphoproteins were identified from 5 μL milk, and the limit of detection is 10 fmol. It is expected that Ti⁴⁺-Brush@MAR would be utilized to enrich both multi-phosphopeptides and mono-phosphopeptides in additional biological or food samples.

Interface-Engineered Hollow Nanospheres with Titanium(IV) Binding Sites and Microwindows as Affinity Probes for Ultrafast and Enhanced Phosphopeptides Enrichment

Enrichment and identification of phosphopeptides in real biological samples are of great significance in many aspects. Herein, Ti⁴⁺-immobilized silica hollow nanospheres were tailored via chelating with phosphonic acid groups produced from dealkylation of phosphonate ester functionalized silica hollow nanospheres, which were synthesized through a single micelle templated method with diethylphosphatoethyltriethoxysilane (DPTES) and tetramethoxysilane (TMOS) as silane precursors under neutral conditions. The characterization results of transmission electron microscopy (TEM), nitrogen sorption isotherms, FT-IR, and energy-dispersive X-ray (EDX) spectroscopy confirmed the successful preparation of Ti⁴⁺-immobilized silica hollow nanospheres (SHS-Ti; approximately 17 nm particle size), which possessed a 10 nm hollow cavity with 1.6 nm micropores on the thin shell (about 3.5 nm). Attributed to the immobilized Ti⁴⁺ and high specific area (396 m²/g), SHS-Ti was applied as a Ti⁴⁺-immobilized metal affinity chromatography (Ti-IMAC) material and showed good specificity, a low limit of detection (5 fmol), high selectivity (tryptic digestion mixture of bovine serum albumin/β-casein, 1000:1 molar ratio), high binding capacity (120 mg/g for pyridoxal 5'-phosphate), and a high binding constant (1.30 × 10³ L/mg). Particularly, benefiting from the unique hollow structure with microwindows on the thin shell, a short transport path, and small mass transfer resistance, SHS-Ti exhibited excellent enrichment speed in which both phosphopeptide loading and elution could be completed in 1 min. The 5298 unique phosphopeptides from 1618 unique phosphoproteins were identified after enrichment by SHS-Ti from 100 μg Jurkat cell lysates within three independent replicates. The results showed that SHS-Ti could be utilized as a novel and promising enrichment probe for phosphopeptide characterization in MS-based phosphoproteomics and related fields.