Abnormal glycosylation with hypersialylated O-glycans in patients with Sialuria

• Published in: Biochimica et biophysica acta 2006-06, Vol.1762 (6), p.598-607
• Main Authors: Wopereis, Suzan, Abd Hamid, Umi M., Critchley, Alison, Royle, Louise, Dwek, Raymond A., Morava, Éva, Leroy, Jules G., Wilcken, Bridget, Lagerwerf, Aart J., Huijben, Karin M.L.C., Lefeber, Dirk J., Rudd, Pauline M., Wevers, Ron A.
• Format: Article
• Language: English
• Subjects: Apolipoprotein C-III; Apolipoproteins C - analysis; Apolipoproteins C - blood; Chromatography, High Pressure Liquid; Core I O-glycans; Glycoproteins - blood; Glycosylation; Humans; Hypersialylation; Isoelectric Focusing; N-Acetylneuraminic Acid - metabolism; N-glycosylation; Nucleotides - analysis; Nucleotides - isolation & purification; O-glycosylation, Sialuria OMIM 269921; Polysaccharides - blood; Polysaccharides - metabolism; Protein Isoforms; Sialic Acid Storage Disease - metabolism; Transferrin - analysis
• ISSN: 0925-4439; 0006-3002; 1879-260X
• DOI: 10.1016/j.bbadis.2006.03.009

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 NeuAcα2,6-containing structures (mainly NeuAcα2-3Galβ1-3[NeuAcα2-6]GalNAc). This may relate to K M differences between GalNAc-α2,6-sialyltransferase and α2,3-sialyltransferases. This is the first study demonstrating that the genetic defect in Sialuria results in a CMP-NeuAc overproduction. Subsequently, increased amounts of α2,6-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.