Pseudotargeted MS Method for the Sensitive Analysis of Protein Phosphorylation in Protein Complexes

Area of Science:

• Proteomics
• Biochemistry
• Molecular Biology

Background:

• Protein phosphorylation is a critical post-translational modification regulating cellular processes.
• Analyzing phosphorylation in minute biological samples, like protein complexes, presents significant challenges due to low abundance.
• Existing methods often require extensive sample preparation, limiting analysis of small sample amounts.

Purpose of the Study:

• To develop a sensitive, enrichment-free method for analyzing protein phosphorylation in minute sample quantities.
• To enhance the identification of phosphopeptides using a pseudotargeted mass spectrometry (MS) approach.
• To quantitatively examine phosphopeptides in endogenous protein complexes.

Main Methods:

• Utilized parallel reaction monitoring (PRM) for sensitive phosphopeptide detection.
• Employed low-confidence phosphopeptides from data-dependent acquisition (DDA) to build a pseudotargeted list for PRM.
• Applied the method to affinity-purified endogenous Shc1 protein complexes without sample fractionation or enrichment.

Main Results:

• Successfully identified 82 phospho-sites in Shc1 protein complexes across four temporal stages of EGF signaling.
• Demonstrated high sensitivity for identifying low-abundance phosphopeptides.
• Achieved the highest number of identified phospho-sites from protein complexes to date.

Conclusions:

• The enrichment-free, pseudotargeted MS method is highly effective for sensitive phosphoproteomic analysis of minute samples.
• This approach facilitates the study of phosphorylation-regulated protein complex assembly.
• The method simplifies targeted analysis by using the same sample and LC system for discovery and targeted phases.