Abnormal glycosylation with hypersialylated O-glycans in patients with Sialuria.
Sialuria is an inborn error of metabolism characterized by coarse face, hepatomegaly and recurrent respiratory tract infections. The genetic defect in this disorder results in a loss of feedback control of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine-kinase by CMP-N-acetylneuraminic acid (CMP-NeuAc) resulting in a substantial overproduction of cytoplasmic free sialic acid. This study addresses fibroblast CMP-NeuAc levels and N- and O-glycan sialylation of serum proteins from Sialuria patients. CMP-NeuAc levels were measured with HPLC in fibroblasts. Isoelectric focusing (IEF) of serum transferrin and of apolipoprotein C-III (apoC-III) was performed on serum of three Sialuria patients. Isoforms of these proteins can be used as specific markers for the biosynthesis of N- and core 1 O-glycans. Furthermore, total N- and O-linked glycans from serum proteins were analyzed by HPLC. HPLC showed a clear overproduction of CMP-NeuAc in fibroblasts of a Sialuria patient. Minor changes were found for serum N-glycans and hypersialylation was found for core 1 O-glycans on serum apoC-III and on total serum O-glycans in Sialuria patients. HPLC showed an increased ratio of disialylated over monosialylated core 1 O-glycans. The hypersialylation of core 1 O-glycans is due to the increase of NeuAcalpha2,6-containing structures (mainly NeuAcalpha2-3Galbeta1-3[NeuAcalpha2-6]GalNAc). This may relate to KM differences between GalNAc-alpha2,6-sialyltransferase and alpha2,3-sialyltransferases. This is the first study demonstrating that the genetic defect in Sialuria results in a CMP-NeuAc overproduction. Subsequently, increased amounts of alpha2,6-linked NeuAc were found on serum core 1 O-glycans from Sialuria patients. N-glycosylation of serum proteins seems largely unaffected. Sialuria is the first metabolic disorder presenting with hypersialylated O-glycans.
Wopereis
Suzan
S
Radboud University Nijmigen Medical Center, Laboratory of Pediatrics and Neurology, The Netherlands, and The Children's Hospital at Westmead, NSW Sydney, Australia.
Abd Hamid
Umi M
UM
Critchley
Alison
A
Royle
Louise
L
Dwek
Raymond A
RA
Morava
Eva
E
Leroy
Jules G
JG
Wilcken
Bridget
B
Lagerwerf
Aart J
AJ
Huijben
Karin M L C
KM
Lefeber
Dirk J
DJ
Rudd
Pauline M
PM
Wevers
Ron A
RA
D053305:Apolipoprotein C-III; D001056:Apolipoproteins C / Q000032:analysis / Q000097:blood; D002851:Chromatography, High Pressure Liquid; D006023:Glycoproteins / Q000097:blood; D006031:Glycosylation; D006801:Humans; D007525:Isoelectric Focusing; D019158:N-Acetylneuraminic Acid / Q000378:metabolism*; D009711:Nucleotides / Q000032:analysis / Q000302:isolation & purification; D011134:Polysaccharides / Q000097:blood / Q000378:metabolism*; D020033:Protein Isoforms; D029461:Sialic Acid Storage Disease / Q000378:metabolism*; D014168:Transferrin / Q000032:analysis
D053305:Apolipoprotein C-III; D001056:Apolipoproteins C; D006023:Glycoproteins; D009711:Nucleotides; D011134:Polysaccharides; D020033:Protein Isoforms; D014168:Transferrin; D019158:N-Acetylneuraminic Acid