PSM for SEYTYGASYR in PeptideAtlas. With an iProphet probability of 1.000, all y ions y1 – y10 are observed, as well as b1 – b8, with many neutral loss ions, internal fragmentation ions, and other corroborating peaks. With a simple mapping search, this peptide appears to be uniquely mapping to a protein not seen anywhere else in PeptideAtlas, a one-hit wonder. With the complex fuzzy mapping capabilities of ProMaST, a potential alternative mapping to a highly variable region of an immunoglobulin is revealed.