Peptides detected as modified by a phosphorylation, sulfation or acetylation using SEQUEST.

Each line represents a group of matches reaching our quality cut-off corresponding to the same peptide sequence with the indicated modification. SEQUEST matches were selected to have a XCorr>2 when peptide charge was +2, >2.5 with peptide charge +3, >3 with peptide charge +4, and >4 with peptide charge >+5. Detail of all peptide matches (modified and unmodified) obtained by both search engines is available as supplementary information (Table S1).