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Mice primary T cell phosphotyrosine proteomics enabled by BOOST

ABSTRACT: Signal propagation mediating numerous cellular processed in T cells is orchestrated by tyrosine phosphorylation with a high degree of regulation1, 2. Because aberrant tyrosine phosphorylation can result in many diseases3, a method to systematically quantify this dynamic process can be helpful in understanding the mechanistic underpinnings of T cell functions. However, accurate quantitation of tyrosine phosphorylation is challenging due to its low abundance4. Mass spectrometry(MS) based phosphotyrosine proteomics has emerged to be an attractive solution for wide scale profiling of the tyrosine phosphoproteome5, 6. Many advances have been made in this field to improve the enrichment efficiency of phosphotyrosine(pTyr)-containing peptides to improve the coverage depth7-11. Separately, computational methods of Fourier transform-(FT)MS such as an Orbitrap analyzer have also made significantly progress in the quantitation of TMT samples. For example, the phase-constrained spectrum deconvolution method (ΦSDM) have been shown to substantially improve the spectral quality and speed of FT-MS instruments12. ΦSDM deconvolves FT spectra into frequency distributions to allow more efficient extraction of the harmonic components of the oscillating ions12. As a result, higher mass resolution and accuracy can be achieved with shorter transient times12. We recently developed the BOOST approach by coupling PV boost channel in a multiplexed TMT approach to significantly increase the quantitative depth of the tyrosine phosphoproteome13. While it has been shown to work in Jurkat cell line, it has not been demonstrated to work in scarce mice primary T cells. Here, we demonstrate the first phosphotyrosine proteomics performed in mice primary T cells using BOOST that enabled the identification of more than 6000 pTyr peptides using only 1 mg of protein. We further demonstrated the importance of ΦSDM, in which when disabled, enabled significantly deeper quantitation depth in low-abundance samples. Using samples with contrived ratios, disabling ΦSDM improved the precision of low-abundance peptides and allowed the quantitation of up to 2-fold more increase in statistically significant ratios.

INSTRUMENT(S): Orbitrap Eclipse

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Primary Cell, T Cell

SUBMITTER: Xien Yu Chua

LAB HEAD: Arthur Salomon

PROVIDER: PXD025853 | Pride | 2021-06-04

REPOSITORIES: Pride

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Project description:Dynamic tyrosine phosphorylation is fundamental to a myriad of cellular processes. However, the inherently low abundance of tyrosine phosphorylation in the proteome and the inefficient enrichment of phosphotyrosine(pTyr)-containing peptides has led to poor pTyr peptide identification and quantitation, critically hindering researchers’ ability to elucidate signaling pathways regulated by tyrosine phosphorylation in systems where cellular material is limited. The most popular approaches to wide-scale characterization of the tyrosine phosphoproteome use pTyr enrichment with pan-specific, anti-pTyr antibodies from a large amount of starting material. Methods that decrease the amount of starting material and increase the characterization depth of the tyrosine phosphoproteome while maintaining quantitative accuracy and precision would enable the discovery of tyrosine phosphorylation networks in rarer cell populations. To achieve these goals, a novel method leveraging the multiplexing capability of tandem mass tags (TMT) and the use of trigger channels – cells treated with the promiscuous tyrosine phosphatase inhibitor pervanadate (PV) – selectively increased the relative abundance of pTyr-containing peptides. After PV facilitated selective fragmentation of pTyr-containing peptides, TMT reporter ions delivered sensitive quantitation of each peptide for the experimental samples while the quantitation from PV trigger channels was ignored. This method yielded up to 6.3-fold boost in quantification depth of statistically significant data derived from contrived ratios, compared to TMT without trigger channels or intensity-based label-free (LF) quantitation while maintaining quantitative accuracy and precision, allowing quantitation of over 2300 unique pTyr peptides from only 1 mg of T cell receptor-stimulated Jurkat T cells. The trigger channel strategy can potentially be applied in analyses of other post-translational modifications where treatments that broadly boost the levels of those modifications across the proteome are available.

Project description:Albeit much less abundant than Ser/Thr phosphorylation (pSer/pThr), Tyr phosphorylation (pTyr) is considered a hallmark in cellular signal transduction. However, its analysis remains a challenge. The conventional immunopurification (IP) approach using antibodies pan-specific to pTyr sites is known to have low sensitivity, poor reproducibility and high cost. SH2 domain-derived pTyr-superbinder is a good replacement of pTyr antibody for the specific enrichment of pTyr peptides for phosphoproteomics analysis. In this study, we aim to optimize the approach using SH2 superbinder for tyrosine phosphoproteome analysis. The present work covalently immobilized SH2 superbinders to agrose beads, designed and evaluated four different SH2 superbinder based experimental workflows for phosphotyrosine analysis. After made a head to head comparison of them, we observed that the combined strategy employing Ti4+-IMAC and covalently immobilized SH2 superbinder enrichment in sequence generated the largest pTyr peptide dataset (3519) with the best selectivity (90%). Next the optimal method was applied for pTyr profiling from normal mouse tissues, and resulted in the identification of 197 pTyr sites (of which 73 were novel) from 5 mg protein digests, which validated its high sensitivity. An comparison with antibody 4G10 by isolating pTyr peptides from 5 mg unstimulated Jurkat cell digests were made, our optimal strategy identified 343 while the antibody 4G10 based method identified 242 pTyr sites, respectively, further confirmed the robustness of the method. Finally, the optimal strategy was applied for quantitative pTyr phosphorylation analysis of EGF stimulated/unstimulated HeLa cells, 261 pTyr sites were successfully quantified from 5 mg stable-isotope dimethyl labling protein digests. In general, the combination of Ti4+-IMAC and SH2 superbinder enrichment in sequence generated a facial and robust strategy for qualitative and quantitative analysis of pTyr proteome.

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Mice primary T cell phosphotyrosine proteomics enabled by BOOST

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