Global Analysis of Endogenously Intact S-Acylated Peptides Reveals Localization Differentiation of Heterogeneous Lipid Chains in Mammalian Cells

Abstract

S-acylation is a widespread lipidation form in eukaryotes in which various fatty acids can be covalently attached to specific cysteine residues. However, due to the low reactivity of the lipid moieties and lack of specific antibodies, purification of intact S-acylated peptides remains challenging. Here, we developed a pretreatment method for direct separation and global analysis of endogenously intact S-acylated peptides by nanographite fluoride-based solid-phase extraction (nGF-SPE), together with the investigation and optimization of the enrichment procedure as well as the LC-MS/MS analysis process. Consequently, we performed the first global profiling of endogenously intact S-acylated peptides, with 701 S-palmitoylated peptides from HeLa cell lysates in a restricted search. Furthermore, coupling the nGF-SPE method with open search mode, altogether 1119 intact S-acylated peptides were identified with the attached palmitate, palmitoleate, myristate, and octanoate chain, respectively, providing a global insight into the endogenously heterogeneous modification state. Notably, we found and validated that S-palmitoleoylation (C16:1) provided less affinity toward lipid rafts compared with S-palmitoylation (C16:0). This study developed the first straightforward way to characterize endogenously intact S-acylated peptides on a proteome-wide scale, providing the modified residues together with their attached lipid moieties simultaneously, which paves the way for further understanding of protein S-acylation.