Fig. 2.

Representative MS spectra of native MS-based affinity screening. (A) MS spectrum of apo-3CLpro during the screening process: 3CLpro mainly presents in charge states P¹⁹⁺ and P¹⁸⁺. (B) Representative MS spectrum of a negative result from fraction 1 of Andrographis paniculata. Representative MS spectra of two positive results from fraction 3 (C) and fraction 6 (D) of Andrographis paniculata. The protein-ligand binary complexes (P + L) were found distinctly and the Δm/z was used to calculate the molecular weight of the ligands. Later, andrographoside and andrographolide were identified in fraction 3 and fraction 6 as compounds 12 and 13, respectively.