Figure 6.

Structure analysis of the Siglec-7 ligand glycan using MS

(A) MS/MS spectrum of PLAG3 domain-derived glycopeptide from Asp-N digested PDPN-Fc peptide. They were analyzed using LC/MS. Tandem mass spectrum of the precursor ion m/z 753.298 (3+) (Table S2) were analyzed using TOF MS/MS. The fragmentation table shows the PLAG domain 3 sequence and its detected product ions in red. The m/z 753.298 (3+) was identified to consist of a PLAG3 domain peptide and a HexNAc, a Hex, and 3 Neu5Ac, as identified using MS and MS/MS analysis. Then, the tandem mass spectrum indicated amino acid sequence of PLAG3 and NeuAc (m/z 274.1 is [NeuAc-H₂O + H] and m/z 292.1 is [NeuAc+H]), NeuAc-HexNAc (m/z 495.2), and NeuAc-Hex-HexNAc (m/z 657.2).

(B) MS/MS spectrum of released and labeled tri-sialylated O-glycan. O-glycan was released by β-elimination and labeled with 1-phenyl-3-methyl-5-pyrazolone (PMP). Tandem mass spectrum of the precursor ion m/z 794.3 (2+) was analyzed using TOF MS/MS.

(C) Predicted glycan structure.