The molecular basis for the absence of N-glycolylneuraminic acid in humans
The molecular basis for the absence of N-glycolylneuraminic acid in humans
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DOI：
10.1074/jbc.273.25.15866
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发表时间：
1998-06-19
影响因子：
4.8
通讯作者：
Suzuki, A
中科院分区：
文献类型：
--
作者：
Irie, A;Koyama, S;Suzuki, A
N-羟基神经氨酸(NeuGc)在大多数哺乳动物中大量表达，但在人类中检测不到。NeuGc的表达受胞苷单磷酸-N-乙酰神经氨酸(CMPNeuAc)羟基酶活性的控制。我们先前克隆了小鼠cMP-NeuAc羟基酶的一个cDNA，并发现人类基因组中含有一个同源基因，我们在这里报道了人类中没有NeuGc的分子基础。我们从HeLa细胞的cDNA文库中克隆了人cMP-NeuAc羟基酶的cDNA。该基因编码一个486个氨基酸的蛋白质，其推导的氨基酸序列缺乏对应于小鼠cMP-NeuAc羟基酶蛋白N端104个氨基酸的结构域，尽管人的蛋白与小鼠羟基酶蛋白的其余部分高度相同(93%)。人类羟基酶的N端截短是由于人类基因组DNA中一个长达92个碱基的外显子的缺失引起的。人类被。在COS-7细胞中表达的羟基酶没有活性，一个缺失N-末端结构域的小鼠羟基酶突变体也没有活性。由人羟基酶和小鼠羟基酶N-末端区域组成的嵌合体显示了该酶的活性。这些结果表明，人的CMP-NeuAc羟基酶同源物是无效的，因为它缺乏一个对酶活性至关重要的N-末端结构域。人的糖偶联物中没有NeuGc是由于编码cMP-NeuAc羟基酶的基因部分缺失。
N-Glycolylneuraminic acid (NeuGc) is abundantly expressed in most mammals, but it is not detectable in humans. The expression of NeuGc is controlled by cytidine monophospho-N-acetylneuraminic acid (CMPNeuAc) hydroxylase activity. We previously cloned a cDNA for mouse CMP-NeuAc hydroxylase and found that the human genome contains a homologue, We report here the molecular basis for the absence of NeuGc in humans. We cloned a cDNA for human CMP-NeuAc hydroxylase from a HeLa cell cDNA library. The cDNA encodes a 486-amino acid protein, and its deduced amino acid sequence lacks a domain corresponding to the N-terminal 104 amino acids of the mouse CMP-NeuAc hydroxylase protein, although the human protein is highly identical (93%) to the rest of the mouse hydroxylase protein. The N-terminal truncation of the human hydroxylase is caused by deletion of a 92-base pair-long exon in human genomic DNA. The human by. droxylase expressed in COS-7 cells exhibited no enzymatic activity, and a mouse hydroxylase mutant, which lacks the N-terminal domain, was also inactive. A chimera composed of the human hydroxylase and the N-terminal domain of the mouse hydroxylase displayed the enzyme activity. These results indicate that the human homologue of CMP-NeuAc hydroxylase is inactive because it lacks an N-terminal domain that is essential for enzyme activity. The absence of NeuGc in human glycoconjugates is due to a partial deletion in the gene that encodes CMP-NeuAc hydroxylase.