The Effect Of Ligand On Protein Conformation:Insight From Ion Mobility Mass Spectrum

Ion mobility mass spectrometry,a new analysis method which combines ion mobility separation with mass spectrum,has become a powerful tool in structural biology analysis.It can determine the structure,topology structure,and the dynamic of analyte simultaneously.Here we use annexin A5,diannexin and BtuF to explore the effect of different ligand like calcium ions and vitamin B12 on protein conformation stability in the gas phase.The protein ions produced by nano-electrospray ionization in the ion mobility mass spectrum,were activated by collision with drift gas in the drift tube and promote its conformation to lose the natural state to unfolding,and then ions be gradually separated according to their charge,mass and size.The ion mobility data were collected by Waters Synapt G2-Si HDMS and then be calibrated with a series of protein standards with known theoretical collision cross sections(CCS).The data reveals that measured CCS of the protein without collisional activation is highly consistent with its expected theoretical CCS in the native state.While as the collision energy increases,ions are activated and conformational changes are produced.And the degree of conformational unfolding induced by the collision energy is related to the stability of the non-covalent interaction between molecules or molecules in the protein complex.The results suggest that the binding of ligand with protein can greatly enhance its structural stability in the gas phase.