scholarly journals Extensive non-canonical phosphorylation in human cells revealed using strong-anion exchange-mediated phosphoproteomics

2017 ◽  
Author(s):  
Gemma Hardman ◽  
Simon Perkins ◽  
Zheng Ruan ◽  
Natarajan Kannan ◽  
Philip Brownridge ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Protein Phosphorylation ◽  
Anion Exchange ◽  
Human Cell ◽  
Cell Biology ◽  
Human Cells ◽  
Phosphopeptide Enrichment ◽  
Cell Extracts ◽  
Strong Anion Exchange ◽  
Acid Labile

Protein phosphorylation is a ubiquitous post-translational modification (PTM) that regulates all aspects of life. To date, investigation of human cell signalling has focussed on canonical phosphorylation of serine (Ser), threonine (Thr) and tyrosine (Tyr) residues. However, mounting evidence suggests that phosphorylation of histidine also plays a central role in regulating cell biology. Phosphoproteomics workflows rely on acidic conditions for phosphopeptide enrichment, which are incompatible with the analysis of acid-labile phosphorylation such as histidine. Consequently, the extent of non-canonical phosphorylation is likely to be under-estimated. We report an Unbiased Phosphopeptide enrichment strategy based on Strong Anion Exchange (SAX) chromatography (UPAX), which permits enrichment of acid-labile phosphopeptides for characterisation by mass spectrometry. Using this approach, we identify extensive and positional phosphorylation patterns on histidine, arginine, lysine, aspartate and glutamate in human cell extracts, including 310 phosphohistidine and >1000 phospholysine sites of protein modification. Remarkably, the extent of phosphorylation on individual non-canonical residues vastly exceeds that of basal phosphotyrosine. Our study reveals the previously unappreciated diversity of protein phosphorylation in human cells, and opens up avenues for exploring roles of acid-labile phosphorylation in any proteome using mass spectrometry.

scholarly journals Identifying specific protein interaction partners using quantitative mass spectrometry and bead proteomes

2008 ◽  
Vol 183 (2) ◽  
pp. 223-239 ◽  
Author(s):  
Laura Trinkle-Mulcahy ◽  
Séverine Boulon ◽  
Yun Wah Lam ◽  
Roby Urcia ◽  
François-Michel Boisvert ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Protein Interaction ◽  
Cell Biology ◽  
Protein Complexes ◽  
Affinity Purification ◽  
Specific Protein ◽  
Protein Interaction Data ◽  
Quantitative Mass Spectrometry ◽  
Cell Extracts ◽  
Interaction Partners

The identification of interaction partners in protein complexes is a major goal in cell biology. Here we present a reliable affinity purification strategy to identify specific interactors that combines quantitative SILAC-based mass spectrometry with characterization of common contaminants binding to affinity matrices (bead proteomes). This strategy can be applied to affinity purification of either tagged fusion protein complexes or endogenous protein complexes, illustrated here using the well-characterized SMN complex as a model. GFP is used as the tag of choice because it shows minimal nonspecific binding to mammalian cell proteins, can be quantitatively depleted from cell extracts, and allows the integration of biochemical protein interaction data with in vivo measurements using fluorescence microscopy. Proteins binding nonspecifically to the most commonly used affinity matrices were determined using quantitative mass spectrometry, revealing important differences that affect experimental design. These data provide a specificity filter to distinguish specific protein binding partners in both quantitative and nonquantitative pull-down and immunoprecipitation experiments.

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