Fig. 4: LODES and CID spectra of tetra-antennary N-glycans.

a LODES for tetra-antennary N-glycans with the tag of (CH₂)₅NH₂ at the reducing end. The LODES of m/z 771 (denoted by the dashed green line) and the LODES of sialic acid (denoted by the dashed red line) in (a) are analogous to that in Fig. 3a. b–d CID spectra of isomer α-2-3 E2. Intensity (ion m/z 448) > intensity (ion m/z 508) in (b) indicates that the isomer belongs to group E [propensity 2(f)]. Intensity (ion m/z 346) > intensity (ion m/z 316) in (c) indicates that the isomer belongs to group E2 [propensity 2(b)]. The ion m/z 406 in (c) includes disaccharides GlcNAc-(1→4)-Man and GlcNAc-(1→2)-Man; thus, the intensity of ion m/z 286 in (c) is not included in the comparison of the intensities of ions m/z 346 and 316. e–g CID spectra of isomer α-2-6 D2. Intensity (ion m/z 448) < intensity (ion m/z 508) in (e) indicates that the isomer belongs to group D [propensity 2(f)]. Intensity (ion m/z 508) > intensity (ion m/z 478) and intensity (m/z = 448) in (f) indicates that the isomer is D2 (propensity 2(b)). A comparison of (d) and (g) with Fig. 3b, c suggests the glycosidic bond of sialic acid is α-2→3 and α-2→6, respectively. The numbers (in green) in the horizontal line at the top of each CID spectrum represent the CID sequence. The number on the top of each peak in CID spectrum represents m/z value, which the structural decisive fragments are highlighted in red boldface.