Novel Two-Dimensional MoS2–Ti4+ Nanomaterial for Efficient Enrichment of Phosphopeptides and Large-Scale Identification of Histidine Phosphorylation by Mass Spectrometry

Due to its key roles in regulating the occurrence and development of cancer, protein histidine phosphorylation has been increasingly recognized as an important form of post-translational modification in recent years. However, large-scale analysis of histidine phosphorylation is much more challenging than that of serine/threonine or tyrosine phosphorylation, mainly because of its acid lability. In this study, MoS2–Ti4+ nanomaterials were synthesized using a solvothermal method and taking advantage of the electrostatic adsorption between MoS2 nanosheets and Ti4+. The MoS2–Ti4+ nanomaterials have the advantage of the combined affinity of Ti4+ and Mo toward phosphorylation under medium acidic conditions (pH = 3), which is crucial for preventing hydrolysis and loss of histidine phosphorylation during enrichment. The feasibility of using the MoS2–Ti4+ nanomaterial for phosphopeptide enrichment was demonstrated using mixtures of β-casein and bovine serum albumin (BSA). Further evaluation revealed that the MoS2–Ti4+ nanomaterial is capable of enriching synthetic histidine phosphopeptides from 1000 times excess tryptic-digested HeLa cell lysate. Application of the MoS2–Ti4+ nanomaterials for large-scale phosphopeptide enrichment results in the identification of 10 345 serine, threonine, and tyrosine phosphosites and the successful mapping of 159 histidine phosphosites in HeLa cell lysates, therefore indicating great potential for deciphering the vital biological roles of protein (histidine) phosphorylation.