Methodology of electrospray ion trap mass spectrometry for analyzing the non-covalent binding of protein and low-molecular-weight ligand

A new MS-titration method for the non-covalent binding of protein-ligand based on the research of berberine and α₁-acid glycoprotein was established. The major presumption of new method is that the total concentration of protein-ligand complex is approximately the same as the total concentration of acting protein if a certain extent of affinity is existed between protein and ligand, in addition, the mole amount of acting ligand is more than that of acting protein. The non-covalent binding behaviours between berberine and α₁-acid glycoprotein was studied by using electrospray ionization ion trap mass spectrometry (ESI-ITMS), and the results were verified by fluorescence quenching method. The results showed that the binding behaviours between berberine and α₁-acid glycoprotein, for example, stability constant, number of binding site, type of the main binding force, were almost the same by using the new MS-titration method and fluorescence quenching method. Comparing with the reported MS-titration method, the presented MS-titration method in this paper is more simple and applicable, does not demand much for the devices, and can lead to reliable results in same cases.