De novo peptide sequencing is the only tool for extracting peptide sequences directly from tandem mass spectrometry (MS) data without any protein database.However,neither the accuracy nor the efficiency of de novo sequencing has been satisfactory,mainly due to incomplete fragmentation information in experimental spectra.Recent advancement in MS technology has enabled acquisition of higher-energy collisional dissociation (HCD) and electron transfer dissociation (ETD) spectra of the same precursor.