Initiation of O-glycan synthesis in IgA1 hinge region is determined by a single enzyme, UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase 2.
The hinge region of human immunoglobulin A1 (*IgA1) possesses multiple O-glycans, of which synthesis is initiated by the addition of GalNAc to serine or threonine through the activity of UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferases (pp-GalNAc-Ts). We found that six pp-GalNAc-Ts, pp-GalNAc-T1, -T2, -T3, -T4, -T6, and -T9, were expressed in B cells, IgA-bearing B cells, and NCI-H929 IgA myeloma cells. pp-GalNAc-T activities of these six enzymes for a synthetic IgA hinge peptide, which has nine possible O-glycosylation sites, were examined using a reversed phase-high performance liquid chromatography, a matrix-assisted laser desorption ionization time of flight mass spectrometry, and peptide sequencing analysis. pp-GalNAc-T2 showed the strongest activity transferring GalNAc to a maximum of eight positions. Other pp-GalNAc-Ts exhibited different substrate specificities from pp-GalNAc-T2; however, their activities were extremely weak. It was reported that the IgA1 hinge region possesses a maximum of five O-glycans, and their amino acid positions have been determined. We found that pp-GalNAc-T2 selectively transferred GalNAc residues to the same five positions. These results strongly suggested that pp-GalNAc-T2 is an essential enzyme for initiation of O-linked glycosylation of the IgA1 hinge region.
Iwasaki
Hiroko
H
Glycogene Function Team, Research Center for Glycoscience, National Institute of Advanced Industrial Science and Technology, Open Space Laboratory C-2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
Zhang
Yan
Y
Tachibana
Kahori
K
Gotoh
Masanori
M
Kikuchi
Norihiro
N
Kwon
Yeon-Dae
YD
Togayachi
Akira
A
Kudo
Takashi
T
Kubota
Tomomi
T
Narimatsu
Hisashi
H
D000595:Amino Acid Sequence; D001402:B-Lymphocytes / Q000201:enzymology / Q000276:immunology; D001483:Base Sequence; D002460:Cell Line; D006801:Humans; D007070:Immunoglobulin A / Q000096:biosynthesis* / Q000737:chemistry*; D007700:Kinetics; D008214:Lymphocytes / Q000201:enzymology / Q000276:immunology*; D008969:Molecular Sequence Data; D009101:Multiple Myeloma / Q000276:immunology; D017350:N-Acetylgalactosaminyltransferases / Q000378:metabolism*; D011134:Polysaccharides / Q000096:biosynthesis*; D012016:Reference Values; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013379:Substrate Specificity; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D014536:Uridine Diphosphate N-Acetylgalactosamine / Q000378:metabolism*; D000097763:Polypeptide N-acetylgalactosaminyltransferase
D007070:Immunoglobulin A; D017350:N-Acetylgalactosaminyltransferases; D011134:Polysaccharides; D014536:Uridine Diphosphate N-Acetylgalactosamine; D000097763:Polypeptide N-acetylgalactosaminyltransferase