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Figure 1 | Proteome Science

Figure 1

From: Phosphoproteomes of Strongylocentrotus purpuratus shell and tooth matrix: identification of a major acidic sea urchin tooth phosphoprotein, phosphodontin

Figure 1

The phosphorylation site of protein SM30-E. This peptide was also identified in a non-phosphorylated version in the present and previous studies [10, 11], indicating that this site is only partially modified. The spectrum shows an uninterrupted series of y ions (y2-y7). This sequence tag, supplemented by some b ions, and the accurate mass of the complete peptide measured in the orbitrap, allowed the identification of this peptide by database searches. The most intense ions, y7 and y4, are due to preferential cleavage N-terminal of proline residues in position 7 and10 of the peptide sequence. This is a well known feature of Pro-containing peptides frequently used for manual validation of peptide assignments. Loss of H3PO4, indicated by —P, is first observed in b9 and y5, indicating phosphorylation of Thr in position 9 of the peptide sequence. Loss of NH3, indicated by -17, frequently occurs upon fragmentation of Asn-containing peptides. Cyclization of N-terminal Gln to pyroglutamate is common in peptides with N-terminal Gln.

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Proteome Science

ISSN: 1477-5956