Advanced mass spectrometry and chemical analyses reveal the presence of terminal disialyl motif on mouse B-cell glycoproteins.
The occurrence of a terminal disialyl motif on mammalian O-glycans is increasingly being identified through recent mass spectrometry (MS)-based glycomic profiling. In most cases, it is carried on simple core 1 structures in which both the galactose and N-acetyl galactosamine can be disialylated. In contrast, a disialyl motif on N-glycans is less readily revealed by MS mapping, since additional MS/MS analysis is required to determine the distribution of the various sialic acids on typically multisialylated complex type N-glycans. In our MS-based glycomic screening, we found that a mouse B lymphoma cell line, BCL1, ranks among those that have the highest amount of disialyl motif on its O-glycans, including those carried on CD45. More intriguingly, detailed chemical and MS/MS analyses unambiguously showed that the Neu5Gcα2-8Neu5Gc disialyl motif is also present on the N-glycans and that it can be carried on the termini of polylactosaminoglycan chains, which can be further sulfated on the proximal GlcNAc, occurring alongside other monosialylated sulfated LacNAc termini. Upon silencing the expression of mouse α2,8-sialyltransferase VI (ST8Sia VI), the overall disialyl content decreases significantly, but more so for that on the N-glycans than the O-glycans. ST8Sia VI was further shown to be the most significantly upregulated ST8Sia during plasma cell differentiation, which coincides with increasing content of the disialyl motif. Increasing terminal disialylation without leading to polysialylation may thus have important biological consequences awaiting further investigation. Likewise, the expression of mono- and disialylated sulfated LacNAc may constitute novel recognition codes modulating B-cell activation and differentiation.
Institute of Biochemical Sciences, National Taiwan University.
Shui-Hua
SH
Wang
Chih-Ming
CM
Tsai
Kuo-I
KI
Lin
Kay-Hooi
KH
Khoo
D000117:Acetylglucosamine / Q000737:chemistry / Q000378:metabolism; D000606:Amino Sugars / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002454:Cell Differentiation; D002478:Cells, Cultured; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism; D006031:Glycosylation; D017493:Leukocyte Common Antigens / Q000737:chemistry / Q000378:metabolism*; D008358:Mannose / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D058977:Molecular Sequence Annotation; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D010950:Plasma Cells / Q000502:physiology; D011499:Protein Processing, Post-Translational; D012794:Sialic Acids / Q000737:chemistry / Q000378:metabolism*; D012799:Sialyltransferases / Q000235:genetics / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D053719:Tandem Mass Spectrometry
D000606:Amino Sugars; D006023:Glycoproteins; D009844:Oligosaccharides; D012794:Sialic Acids; C000458:N-acetyllactosamine; D012799:Sialyltransferases; D017493:Leukocyte Common Antigens; C516770:Ptprc protein, mouse; C464440:alpha2,8-sialyltransferase VI; D008358:Mannose; D000117:Acetylglucosamine
ST8Sia; disialyl; glycomics; mass spectrometry; plasma cell differentiation