ATP-Coated Dual-Functionalized Titanium(IV) IMAC Material for Simultaneous Enrichment and Separation of Glycopeptides and Phosphopeptides

Comprehensive PTM profiling with SCASP-PTM uncovers mechanisms of p62 degradation and ALDOA-mediated tumor progression

Multiple post-translational modification (PTM) proteomics typically combines PTM enrichment with multiplex isobaric labeling and peptide fractionation. However, effective methods for sequentially enriching multiple PTMs from a single sample for data-independent acquisition mass spectrometry (DIA-MS) remain lacking. We present SDS-cyclodextrin-assisted sample preparation (SCASP)-PTM, an approach that enables desalting-free enrichment of diverse PTMs, including phosphopeptides, ubiquitinated peptides, acetylated peptides, glycopeptides, and biotinylated peptides. SCASP-PTM uses SDS for protein denaturation, which is sequestered by cyclodextrins before trypsin digestion, facilitating sequential PTM enrichment without additional purification steps. Combined with DIA-MS, SCASP-PTM quantifies the proteome, ubiquitinome, phosphoproteome, and glycoproteome in HeLa-S3 cell samples, identifying serine 28 phosphorylation as a key driver of poly(I:C)-induced p62 degradation. This method also quantifies PTMs in clinical tissue samples, revealing the critical role of ALDOA K330 ubiquitination/acetylation in tumor progression. SCASP-PTM offers a streamlined workflow for comprehensive PTM analysis in both basic research and clinical applications.

Immobilized metal ion affinity chromatography: waltz of metal ions and biomacromolecules

INTRODUCTION

Immobilized metal ion affinity chromatography (IMAC) is an effective method developed in the 1980s for the separation and purification of proteins. The system consists of a solid-phase matrix, a linking ligand, and a metal ion. The method is based on the ability of metal ions to bind specifically to certain specific amino acid residues of proteins, thereby selectively enriching and purifying proteins.

AREAS COVERED

This review aims to describe current knowledge of fundamental principle of IMAC and summarize the supports, chelating ligands, and metal ions of IMAC. In addition, how IMAC technology is used in proteomics and DNA research are highlighted.

EXPERT OPINION

Over the past decades, IMAC has been extensively utilized as a predominant technique for protein enrichment in a variety of biological and medical research, such as disease diagnosis, tumor biomarker identification, protein purification, and nucleic acid research. In the future, IMAC should be integrated with other proteomics technologies to promote the applications of metalloproteomes in disease diagnosis, metallodrug development and clinical translation.

Metal ion-enhanced ZIC-cHILIC StageTip for N-Glycoproteomic and Phosphoproteomic Profiling in EGFR-mutated Lung Cancer Cells

Surface glycosylation and intracellular phosphorylation regulates the cell-cell communication and signaling cascades. Due to complex glycosylation and dynamic phosphorylation, exploring their interplay remains technically challenging. In this study, we reported a tandem ZIC-cHILIC StageTip strategy for streamlined and simultaneous (sialo)glycoproteomic and phosphoproteomic profiling. We first demonstrated that Fe ions expand the utility of ZIC-cHILIC strategy to phosphoproteomic analysis with greatly enhanced >4-fold coverage and high specificity for mono-phosphopeptides (95%). The Fe-ZIC-cHILIC tandem tips, leveraging stepwise fractionation, enable large-scale coverage of 10,536 glycopeptides, including highly confident 4,285 sialoglycopeptpides, and 11,329 phosphopeptides in a single cell type. To study the mechanism underlying the tyrosine kinase inhibitor (TKI) resistance in non-small cell lung cancer (NSCLC), application of the strategy to 4 NSCLC cells harboring different EGFR mutations reveals significantly differential 1,559 glycopeptides and 1,949 phosphopeptides either in EGFR mutation or TKI resistant cells. Without protein immunoprecipitation, the approach identified FDA-approved drug targets, such as EGFR, ERBB2, MET, and integrin family members. Most prominent alterations were observed in EGFR (auto-phosphorylation Y1197 and 10 bi- and triantennary fucosyl-sialo glycans at N603), downstream PI3K-Akt pathway (ERBB2-T1240, MET-S990/T992, AKT-S124/S126) and integrin family (sialo-fucosyl glycans), suggesting site-specific alteration between N-glycosylation and phosphorylation interplay in the TKI resistant L858R-T790M mutant NSCLC cells. The glycoproteomic and phosphoproteomic landscape may help to unravel the complex modification alterations underlying the resistant mechanism, offering insights for improving therapeutic strategies and patient outcomes.

Standards-Free Absolute Quantitation of Oxidizable Glycopeptides by Coulometric Mass Spectrometry

Currently, glycopeptide quantitation is mainly based on relative quantitation due to absolute quantitation requiring isotope-labeled or standard glycopeptides which may not be commercially available or are very costly and time consuming to synthesize. To address this grand challenge, coulometric mass spectrometry (CMS), based on the combination of electrochemistry (EC) and mass spectrometry (MS), was utilized to quantify electrochemically active glycopeptides without the need of using standard materials. In this study, we studied tyrosine-containing glycopeptides, NYIVGQPSS(β-GlcNAc)TGNL-OH and NYSVPSS(β-GlcNAc)TGNL-OH, and successfully quantified them directly with CMS with a discrepancy of less than 5% between the CMS measured amount and the theoretical amount. Taking one step further, we applied this approach to quantify glycopeptides generated from the digestion of NIST mAb, a monoclonal antibody reference material. Through HILIC column separation, five N297 glycopeptides resulting from NIST mAb tryptic digestion were successfully separated and quantified by CMS for an absolute amount without the use of any standard materials. This study indicates the potential utility of CMS for quantitative proteomics research.

TIMAHAC: Streamlined Tandem IMAC-HILIC Workflow for Simultaneous and High-Throughput Plant Phosphoproteomics and N-glycoproteomics

Protein post-translational modifications (PTMs) are crucial in plant cellular processes, particularly in protein folding and signal transduction. N-glycosylation and phosphorylation are notably significant PTMs, playing essential roles in regulating plant responses to environmental stimuli. However, current sequential enrichment methods for simultaneous analysis of phosphoproteome and N-glycoproteome are labor-intensive and time-consuming, limiting their throughput. Addressing this challenge, this study introduces a novel tandem S-Trap-IMAC-HILIC (S-Trap: suspension trapping; IMAC: immobilized metal ion affinity chromatography; HILIC: hydrophilic interaction chromatography) strategy, termed TIMAHAC, for simultaneous analysis of plant phosphoproteomics and N-glycoproteomics. This approach integrates IMAC and HILIC into a tandem tip format, streamlining the enrichment process of phosphopeptides and N-glycopeptides. The key innovation lies in the use of a unified buffer system and an optimized enrichment sequence to enhance efficiency and reproducibility. The applicability of TIMAHAC was demonstrated by analyzing the Arabidopsis phosphoproteome and N-glycoproteome in response to abscisic acid (ABA) treatment. Up to 1954 N-glycopeptides and 11,255 phosphopeptides were identified from Arabidopsis, indicating its scalability for plant tissues. Notably, distinct perturbation patterns were observed in the phosphoproteome and N-glycoproteome, suggesting their unique contributions to ABA response. Our results reveal that TIMAHAC offers a comprehensive approach to studying complex regulatory mechanisms and PTM interplay in plant biology, paving the way for in-depth investigations into plant signaling networks.

An efficient strategy with a synergistic effect of hydrophilic and electrostatic interactions for simultaneous enrichment of N- and O-glycopeptides

N- and O-glycosylation modifications of proteins are closely linked to the onset and development of many diseases and have gained widespread attention as potential targets for therapy and diagnosis. However, the low abundance and low ionization efficiency of glycopeptides as well as the high heterogeneity make glycosylation analysis challenging. Here, an enrichment strategy, using Knoevenagel copolymers modified with polydopamine-adenosine (denoted as PDA-ADE@KCP), was firstly proposed for simultaneous enrichment of N- and O-glycopeptides through the synergistic effects of hydrophilic and electrostatic interactions. The adjustable charged surface and hydrophilic properties endow the material with the capability to achieve effective enrichment of intact N- and O-glycopeptides. The experimental results exhibited excellent selectivity (1 : 5000) and sensitivity (0.1 fmol μL-1) of the prepared material for N-glycopeptides from standard protein digest samples. Moreover, it was further applied to simultaneous capturing of N- and O-glycopeptides from mouse liver protein digests. Compared to the commercially available zwitterionic hydrophilic interaction liquid chromatography (ZIC-HILIC) material, the number of glycoproteins corresponding to all N- and O-glycopeptides enriched with PDA-ADE@KCP was much more than that with ZIC-HILIC. Furthermore, PDA-ADE@KCP captured more O-glycopeptides than ZIC-HILIC, revealing its superior performance in O-glycopeptide enrichment. All these results indicated that the strategy holds immense potential in characterizing N- and O-intact glycopeptides in the field of proteomics.

Cotton Ti-IMAC: Developing Phosphorylated Cotton as a Novel Platform for Phosphopeptide Enrichment

Protein phosphorylation is an important post-translational modification (PTM), which is involved in many important cellular functions. Understanding protein phosphorylation at the molecular level is critical to deciphering its relevant biological processes and signaling networks. Mass spectrometry (MS) has become a powerful tool for the comprehensive profiling of protein phosphorylation. Yet the low ionization efficiency and low abundance of phosphopeptides among complex biological samples make its MS analysis challenging; an enrichment strategy with high efficiency and selectivity is always necessary prior to MS analysis. In this study, we developed a phosphorylated cotton-fiber-based Ti(IV)-IMAC material (termed as Cotton Ti-IMAC) that can serve as a novel platform for phosphopeptide enrichment. The cotton fiber can be effectively grafted with phosphate groups covalently in a single step, where the titanium ions can then be immobilized to enable capturing phosphopeptides. The material can be prepared using cost-effective reagents within only 4 h. Benefiting from the flexibility and filterability of cotton fibers, the material can be easily packed as a spin-tip and make the enrichment process convenient. Cotton Ti-IMAC successfully enriched phosphopeptides from protein standard digests and exhibited a high selectivity (BSA/β-casein = 1000:1) and excellent sensitivity (0.1 fmol/μL). Moreover, 2354 phosphopeptides were profiled in one LC-MS/MS injection after enriching from only 100 μg of HeLa cell digests with an enrichment specificity of up to 97.51%. Taken together, we believe that Cotton Ti-IMAC can serve as a widely applicable and robust platform for achieving large-scale phosphopeptide enrichment and expanding our knowledge of phosphoproteomics in complex biological systems.