Explanation to pull-down protein LC-MS: In the life of an organism, the function of proteins is achieved by the interaction between proteins and proteins. Therefore, the study of new proteins can provide new directions for the study of the potential function of proteins. In many protein tests, pull-down assays are often used to test protein-protein-interaction. Pull-down's experiment uses highly purified and enriched bait protein to capture the targeted proteins that specifically interact with the bait protein in the cell, and greatly improve the efficiency of identification of new target protein. The specific steps of pull-down's experiment are to express the bait protein modified with poly-His, or Biotin tags. Using immobilized affinity ligand to link the bait protein to the solid-phase matrix, and then mix the bait protein with the protein sample. In this process, targeted protein specifically interacts with the bait protein, and thus, the targeted proteins are isolated from the protein sample mixture. This process can be used to isolate and concentrate a particular protein from a sample containing many thousands of different proteins. Identification of the target protein is then processed by the mass spectrometer.