Phospho-iTRAQ data article: Assessing isobaric labels for the large-scale study of phosphopeptide stoichiometry

Area of Science:

• Proteomics
• Biochemistry
• Mass Spectrometry

Background:

• Accurate quantitation of protein phosphorylation stoichiometry is crucial for understanding cellular signaling.
• Existing phosphoproteomics methods face challenges in ionization, fragmentation, and phospho-enrichment, limiting stoichiometric analysis.
• Distinguishing high and low stoichiometry phosphopeptides is essential for comprehensive discovery.

Purpose of the Study:

• To develop and validate a novel method, Phospho-iTRAQ, for precise quantitation of phosphopeptide stoichiometry.
• To overcome limitations of current phosphoproteomics techniques by focusing on unmodified peptide counterparts.
• To enable multiplexed and simultaneous proteome comparisons for robust phosphorylation analysis.

Main Methods:

• The Phospho-iTRAQ method utilizes differential labeling of peptide samples before phosphatase treatment.
• It quantifies stoichiometry by analyzing the unmodified counterparts of phosphorylated peptides.
• The technique was validated using internal standards in complex cell lysates and employed gel fractionation for extended proteome coverage.

Main Results:

• Phospho-iTRAQ successfully quantifies phosphopeptide stoichiometry, overcoming common analytical hurdles.
• The method demonstrated flexibility and robustness across multiple mass spectrometry platforms.
• Validation in control and EGF-stimulated HeLa cells confirmed its applicability in complex biological samples.

Conclusions:

• Phospho-iTRAQ offers a reliable approach for accurate phosphopeptide stoichiometry measurement.
• The method's focus on unmodified peptides circumvents common phosphoproteomics limitations.
• This technique enhances the discovery of true phosphorylation extents and supports stringent data analysis.