MALDI-TOF or MALDI-tandem TOF analysis of precursor peptide ions from in-solution tryptic digestion of solubilized wrapping silk.
A, MS analysis reveals the presence of precursor ion masses that are identical to products from the theoretical tryptic digestion of the translated AgSF2 cDNA. Subsequently, MS/MS analyses confirmed precursor ions with m/z 1144.5 and 1574.8 have the sequences HFLGGLGNMAK and GGHLLGPLGGLLNTAGK, respectively (boxed region). In these peptides sequences, the underlined Leu residues were determined to be the amino acid Ile (an isobaric residue) in the translated AgSF2 sequence. B, high energy collision-activated dissociation spectrum of precursor ion with m/z 813.4 (MH+, monoisotopic). The sequence of this peptide was found to be GGHPGFGGK. C, high energy collision-activated dissociation spectrum of precursor ion with m/z 1580.7 (MH+, monoisotopic). The sequence of this peptide was found to be GGHPGFGGTGGHPGFGGK. Both precursor ions with m/z 813.4 and 1580.7 after de novo sequencing were found to be present within the translated AgSF1 cDNA sequence.