Simultaneous and site-specific profiling of heterogeneity and turnover in protein S -acylation by intact S -acylated peptide analysis with a cleavable bioorthogonal tag.

Protein S -acylation is an important lipid modification characteristic for heterogeneity in the acyl chain and dynamicity in the acylation/deacylation cycle. Most S -acylproteomic research has been limited by indirect identification of modified proteins/peptides without attached fatty acids, resulting in the failure to precisely characterize S -acylated sites with attached fatty acids. The study of S -acylation turnover is still limited at the protein level. Herein, aiming to site-specifically profile both the heterogeneity and the turnover of S -acylation, we first developed a site-specific strategy for intact S -acylated peptide analysis by introducing an acid cleavable bioorthogonal tag into a metabolic labelling method (ssMLCC). The cleavable bioorthogonal tag allowed for the selective enrichment and efficient MS analysis of intact S -acylated peptides so that S -acylated sites and their attached fatty acids could be directly analysed, enabling the precise mapping of S -acylated sites, as well as circumventing false positives from previous studies. Moreover, 606 S -palmitoylated (C16:0) sites of 441 proteins in HeLa cells were identified. All types of S -acylated peptides were further characterized by an open search, providing site-specific profiling of acyl chain heterogeneity, including S -myristoylation, S -palmitoylation, S -palmitoleylation, and S -oleylation. Furthermore, site-specific monitoring of S -palmitoylation turnover was achieved by coupling with pulse-chase methods, facilitating the detailed observation of the dynamic event at each site in multi-palmitoylated proteins, and 85 rapidly cycling palmitoylated sites in 79 proteins were identified. This study provided a strategy for the precise and comprehensive analysis of protein S -acylation based on intact S -acylated peptide analysis, contributing to the further understanding of its complexity and biological functions.