Figure 2

MS BLAST identification of a spot from group Y. Panel A: nanoES mass spectrum of the unseparated in-gel tryptic digest. Peaks of trypsin autolysis products are designated with "T". Peptide precursor ions, whose tandem mass spectra were acquired and interpreted are designated with corresponding m/z and charge (in parenthesis). Panel B: MS/MS spectrum of the precursor ion with m/z 744.77 (designated with asterisk in panel A). De novo sequencing was performed by considering mass differences between the adjacent peaks in the series of fragments that belong to the ions containing C-terminal amino acid residue (y-ions), starting from high m/z region of the spectrum. The sequence shown in the panel was deduced by considering the most abundant fragment ions and was not necessarily correct; a few optional variants of interpretations based on the low abundant fragments and arriving to the typical tryptic C-terminus (K) were possible. All sequence candidates for used in a single MS BLAST search. Panel C: MS BLAST query that comprises all sequence proposals obtained by the interpretation of all tandem mass spectra were assembled in an arbitrary order and spaced by a minus (gap) symbol. B stands for a generic trypsin cleavage site (R or K) preceding peptide sequences and is introduced if it was possible to read out the sequence until the very N-terminus of the peptide. Panel D: The top confident hit of MS BLAST search. The search also reported a few homologous proteins from other species.