Wopereis Suzan, Abd Hamid Umi M, Critchley Alison, Royle Louise, Dwek Raymond A, Morava Eva, Leroy Jules G, Wilcken Bridget, Lagerwerf Aart J, Huijben Karin M L C, Lefeber Dirk J, Rudd Pauline M, Wevers Ron A
Radboud University Nijmigen Medical Center, Laboratory of Pediatrics and Neurology, The Netherlands, and The Children's Hospital at Westmead, NSW Sydney, Australia.
Biochim Biophys Acta. 2006 Jun;1762(6):598-607. 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 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.
唾液酸尿症是一种先天性代谢紊乱疾病，其特征为面容粗糙、肝肿大和反复呼吸道感染。该疾病的基因缺陷导致CMP-N-乙酰神经氨酸（CMP-NeuAc）对UDP-N-乙酰葡糖胺2-表异构酶/N-乙酰甘露糖胺激酶的反馈控制丧失，从而导致细胞质游离唾液酸大量过量产生。本研究探讨了唾液酸尿症患者成纤维细胞中CMP-NeuAc水平以及血清蛋白的N-糖基化和O-糖基化唾液酸化情况。用高效液相色谱法（HPLC）测定成纤维细胞中的CMP-NeuAc水平。对三名唾液酸尿症患者的血清进行了血清转铁蛋白和载脂蛋白C-III（apoC-III）的等电聚焦（IEF）分析。这些蛋白质的异构体可作为N-糖链和核心1 O-糖链生物合成的特异性标志物。此外，通过HPLC分析血清蛋白中的总N-糖链和O-糖链。HPLC显示一名唾液酸尿症患者的成纤维细胞中CMP-NeuAc明显过量产生。在唾液酸尿症患者的血清N-糖链中发现了微小变化，在血清apoC-III和总血清O-糖链的核心1 O-糖链上发现了高唾液酸化现象。HPLC显示二唾液酸化核心1 O-糖链与单唾液酸化核心1 O-糖链的比例增加。核心1 O-糖链的高唾液酸化是由于含NeuAcalpha2,6结构（主要是NeuAcalpha2-3Galbeta1-3[NeuAcalpha2-6]GalNAc）的增加。这可能与GalNAc-alpha2,6-唾液酸转移酶和alpha2,3-唾液酸转移酶之间的米氏常数差异有关。这是第一项证明唾液酸尿症的基因缺陷导致CMP-NeuAc过量产生的研究。随后，在唾液酸尿症患者的血清核心1 O-糖链上发现了增加的alpha2,6-连接的NeuAc。血清蛋白的N-糖基化似乎基本未受影响。唾液酸尿症是第一种出现O-糖链高唾液酸化的代谢紊乱疾病。
