Sorting Signals, N-Terminal Modifications and Abundance of the Chloroplast Proteome
Figure 5
Tandem MS spectra of N-terminally acetylated peptides suggest presence of two isoforms of Cysteine Synthase, AT2G43750.1.
(A) Tandem MS spectrum of doubly charged 25 aa-long, N-terminally acetylated AVSIKPEAGVEGLNIADNAAQLIGK peptide. Precursor ion is indicated with red asteric. Singly charged y ions are indicated by blue lines with corresponding aa residues shown on top - peptide sequence should be read right-to-left, starting with the most massive y(20) ion. Singly charged b ions are indicated by red lines with corresponding aa residues shown top – peptide sequence should be read left-to-right, starting with the lightest b(4) ion. Ions, whose presence strengthen the assignment of the N-terminal acetylation, b0(4), y++(23), and y++(24) are also indicated. (B) Tandem MS spectrum of doubly charged 24 aa-long, N-terminally acetylated VSIKPEAGVEGLNIADNAAQLIGK peptide. Precursor ion is indicated with red asteric. Singly charged y ions are indicated by blue lines with corresponding aa residues shown on top - peptide sequence should be read from right-to-left, starting with the most massive y(20) ion. Ions, whose presence strengthen the assignment of the N-terminal acetylation, y++(21), and y++(23) are also indicated.