Reconstruction of a N-linked glycan at Asn667. (A) Spectrum as provided by Byonic software. In blue, the b-ions, and in red, the y-ions are depicted. In green, the glycan moieties are indicated as identified by Byonic software. (B) Corresponding glycan moieties depicted in the commonly used cartoons: green circles, blue squares, purple diamonds, and yellow circles for mannose, GlcNAc, sialic acid, and galactose, respectively. From this spectrum, we can determine the glycan structure attached to this asparagine. Starting with the core structure 2-GlcNAc-3-mannose, from the spectrum, we can conclude that this is a complex type glycan; a GlcNAc-galactose-sialic acid fragment is present. The presence of a fucose moiety suggests that this glycan is fucosylated. The fragment corresponding to the mass of the peptide + HexNAc + fucose suggests that the first GlcNAc is fucosylated. Combining these individual fragments results in the final structure of a fucosylated biantennary complex glycan structure attached to Asn667.