Stable isotope labeling-based two-step derivatization strategy for analysis of Phosphopeptides

Area of Science:

• Biochemistry
• Analytical Chemistry
• Proteomics

Background:

• Site-specific protein phosphorylation analysis is challenging.
• Existing chemical derivatization methods for phosphopeptide identification have limitations, including incomplete conversion and high reagent costs.
• Accurate identification and quantification of phosphopeptides are crucial for understanding cellular processes.

Purpose of the Study:

• To develop and validate a cost-effective, two-step chemical derivatization method for accurate site-specific phosphopeptide identification.
• To improve the sensitivity and reliability of phosphopeptide analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS).
• To demonstrate the method's utility in identifying endogenous phosphopeptides in complex biological samples like human saliva.

Main Methods:

• A two-step chemical derivatization using methylamine and dimethylamine (including stable isotopes like dimethylamine-d6) was employed.
• Methylamine neutralizes carboxyl groups to reduce non-specific peptide adsorption.
• Dimethylamine facilitates stable isotope labeling of phosphorylation sites, generating distinct reporter ions (m/z 58.07 and 64.10) for identification and quantification.
• Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and parallel reaction monitoring (PRM) were utilized for peptide analysis.
• Proteomic software was used to screen reporter ions for phosphopeptide identification.

Main Results:

• The derivatization method significantly enhanced ionization and product ion formation of phosphopeptides.
• Stable isotope labeling with dimethylamine-d0 and dimethylamine-d6 enabled the generation of specific reporter ions.
• The method allowed for the distinction of isomeric phosphopeptides based on their phosphorylation sites.
• Using parallel reaction monitoring (PRM), 29 endogenous phosphopeptides were reliably identified in a small volume (10 μL) of human saliva.
• The method demonstrated high efficiency, cost-effectiveness, and improved sensitivity compared to existing techniques.

Conclusions:

• The developed two-step chemical derivatization strategy is highly effective for site-specific phosphopeptide identification.
• This method offers improved sensitivity, cost-effectiveness, and comprehensive product ion coverage for phosphoproteomics.
• The successful identification of endogenous phosphopeptides in human saliva highlights its potential for large-scale phosphoproteomics research.
• The strategy advances the field by providing a reliable tool for accurate phosphoprotein and phosphopeptide analysis.