Fig. 4
Terminal epitopes among different species. (A) The spectral counts of MS/MS scans containing N-glycan with sialic acid were shown in black and N-glycan with acetylated sialic acid were marked in white. The oxonium ions that were utilized to filter their represent structures were [HexNac]+= 204.087; [NeuAc-H2O]+= 274.092; [NeuAc]+= 292.103; [acetylNeuAc]+= 334.113 [HexNac + Hex]+= 366.139. The required ions are shown in the figure legend and the mass tolerance was 10 ppm. CG stands for choriogonadotropin from Sigma. The data was first processed by Byonic with MS/MS filtering function and the spectra counts was counted by inhouse script. (B) MS profile demonstrating the glycoforms on site N31 from human choriogonadotropin subunit beta variant 2 (Swissprot accession#: Q6NT52). (C) The MS/MS spectrum of m/z 894.886 (+ 4) showing that this tryptic peptide was carried with biantenna structures with two sialic acids. The products A and B are shown exemplary. Products C and D do not differ and are shown in supplementary Figure S5.
