Isobaric Stable Isotope N‐Phosphorylation Labeling (iSIPL) for Ultrasensitive Proteome Quantification.

Stable isotope chemical labeling methods have been widely used for high‐throughput mass spectrometry (MS)‐based quantitative proteomics in biological and clinical applications. However, the existing methods are far from meeting the requirements for high sensitivity detection. In the present study, a novel isobaric stable isotope N‐phosphorylation labeling (iSIPL) strategy was developed for quantitative proteome analysis. The tryptic peptides were selectively labeled with iSIPL tag to generate the novel reporter ions containing phosphoramidate P−N bond with high intensities under lower collision energies. iSIPL strategy are suitable for peptide sequencing and quantitative analysis with high sensitivity and accuracy even for samples of limited quantity. Furthermore, iSIPL coupled with affinity purification and mass spectrometry was applied to measure the dynamics of cyclin dependent kinase 9 (CDK9) interactomes during transactivation of the HIV‐1 provirus. The interaction of CDK9 with PARP13 was found to significantly decrease during Tat‐induced activation of HIV‐1 gene transcription, suggesting the effectiveness of iSIPL strategy in dynamic analysis of protein‐protein interaction in vivo. More than that, the proposed iSIPL strategy would facilitate large‐scale accurate quantitative proteomics by increasing multiplexing capability. [ABSTRACT FROM AUTHOR]