HCD MS/MS spectrum (@ 30V) of a tryptic glycopeptide of Gp20 shows near saturation of consecutive Thr residues with the <i>O</i>-HexNAc modification.

<p>The precursor ion [M + 4H]<sup>4+</sup> <i>m/z</i> 1001.9305 has a monoisotopic mass corresponding to that calculated for the peptide </p><p><sub>(87)</sub>EGEETDENTDETTTTTTTASPKPK<sub>(110)</sub></p> plus seven HexNAc residues (Δ 0.5 ppm). There is a prominent HexNAc oxonium ion (<i>m/z</i> 204.0868) and full series of b and y ions, some of which contain one (*) or two (**) HexNAc residues. All ions are singly charged, except where indicated. In addition, charge-reduced ions, all 2+, which correspond to species that have undergone consecutive losses of HexNAc residues, are labeled as follows: ‡** = [M + 2H]<sup>2+</sup>—HexNAc<sub>5</sub> (<i>m/z</i> 1495.1470), ‡* = [M + 2H]<sup>2+</sup>—HexNAc<sub>6</sub> (<i>m/z</i> 1393.6224), ‡ = [M + 2H]<sup>2+</sup> aglycon peptide (<i>m/z</i> 1292.0851).<p></p>