Recent Advances of Native Mass Spectrometry Techniques

Nearly all the life activities are regulated by the interactions of the protein with other biomolecules, including protein-protein interactions (PPIs) and protein-ligand interactions (PLIs), therefore understanding interaction and structural characterization of formed complexes represent a key task for modern bioscience. Conventional biophysical techniques like circular dichroism spectroscopy (CD), fluorescence resonance energy transfer (FRET), surface plasmon resonance (SPR), and isothermal titration calorimetry (ITC), are limited in studying protein complexes structures and interactions, considering sample purity is a major issue for obtaining reliable data with conventional methods mentioned above. Additional technologies are required to complement structural biology and interactomics research, while mass spectrometry (MS) can deal with impurities or even mixtures in principle, therefore native mass spectrometry (nMS) is demonstrated as a powerful tool to bridge the gap between structural biology and interactomics research. As the most widespread soft ionization technique, electrospray ionization is utilized in native mass spectrometry, which employs volatile aqueous solution, near physiological pH and gentle desolvation conditions to make the transfer of weakly bound noncovalent complexes into the gas phase while preserving their integrity and native structure possible. In this way, stoichiometry, binding partners, thermodynamics, structural dynamics, and topology information on transferred noncovalent complexes can be acquired. A recent breakthrough in native MS sample preparation demonstrated direct analysis of overexpressed proteins from crude cell lysates, which significantly simplified sample purification procedures. Innovations in mass spectrometry instruments, such as extended m/z range quadrupole stages or modification of Orbitrap instruments allow access to high mass with little compromise in resolving power. This has promoted the native analysis of protein complexes and diverse protein interaction networks to elucidate their architecture, as well as enabled the identification of small differences in proteoforms. While coupling with either ion mobility spectrometry (IMS) or capillary electrophoresis (CE), the analytical ability of native MS can be greatly extended. In this review, the technologies in native mass spectrometry and several cases in recent reports from five aspects were introduced, such as sample preparation, ion source, instrumentation, ion mobility mass spectrometry and coupling with capillary electrophoresis, challenges for the future development of native mass spectrometry.