Table 1.

Short description of native and affinity MS methods.

	Description	References
1. Affinity selection
Magnetic microbead affinity selection screening (MagMASS)	MagMASS is a solid-phase alternative that complements the solution-phase screening approaches. MagMASS involves tethering the target to magnetic microbeads, incubating the immobilized protein with a natural product mixture, using magnetism to separate the ligand-protein/bead complexes from unbound compounds, and then releasing the bound ligands for UHPLC-MS analysis.	[16]
Pulsed ultrafiltration (PUF) AS-MS.	PUF AS-MS screening begins with the incubation of a mixture of compounds, such as a natural product extract with a solution-phase macromolecular receptor (protein, enzyme, or RNA). After equilibrium is achieved, ultrafiltration is used to separate the large ligand-receptor complexes from the unbound low-mass compounds. Because large pore sizes enable faster ultrafiltration separation, the pore size of the ultrafiltration membrane should be as large as possible while still retaining the macromolecular receptor.	[16]
Collision-induced affinity selection mass spectrometry (CIAS-MS)	Collision-induced affinity selection mass spectrometry (CIAS-MS) is a new method that relies on the affinity between a protein and its ligand for the identification of ligands.	[15]
Size exclusion chromatography (SEC) AS-MS	SEC AS-MS is a solution-phase screening approach like PUF AS-MS that begins with the incubation of a mixture of possible ligands with a macromolecular receptor. After equilibrium is achieved, SEC is used to separate the large ligand-receptor complexes from smaller, unbound compounds. The high mass complexes elute first during SEC and are then denatured using an organic solvent to release the ligands for reversed-phase LC-MS analysis.	[16]
2. Native MS
Bioassay-guided fractionation-MS	This involves the analysis and characterization of molecules whereby the native structural features of the analytes are retained as much as possible. It provides binding informationabout each compound towards the protein of interest.	[17]