Augustin A, Muller-Steffner H, Schuber F
Laboratoire de Chimie Bioorganique, UMR 7514 CNRS-ULP, Faculté de Pharmacie, 74 route du Rhin, 67400 Strasbourg-Illkirch, France.
Biochem J. 2000 Jan 1;345 Pt 1(Pt 1):43-52. doi: 10.1042/bj3450043.
Bovine spleen ecto-NAD(+) glycohydrolase, an archetypal member of the mammalian membrane-associated NAD(P)(+) glycohydrolase enzyme family (EC 3.2.2.6), displays catalytic features similar to those of CD38, i.e. a protein originally described as a lymphocyte differentiation marker involved in the metabolism of cyclic ADP-ribose and signal transduction. Using amino acid sequence information obtained from NAD(+) glycohydrolase and from a truncated and hydrosoluble form of the enzyme (hNADase) purified to homogeneity, a full-length cDNA clone was obtained. The deduced sequence indicates a protein of 278 residues with a molecular mass of 31.5 kDa. It predicts that bovine ecto-NAD(+) glycohydrolase is a type II transmembrane protein, with a very short intracellular tail. The bulk of the enzyme, which is extracellular and contains two potential N-glycosylation sites, yields the fully catalytically active hNADase which is truncated by 71 residues. Transfection of HeLa cells with the full-length cDNA resulted in the expression of the expected NAD(+) glycohydrolase, ADP-ribosyl cyclase and GDP-ribosyl cyclase activities at the surface of the cells. The bovine enzyme, which is the first 'classical' NAD(P)(+) glycohydrolase whose structure has been established, presents a particularly high sequence identity with CD38, including the presence of 10 strictly conserved cysteine residues in the ectodomain and putative catalytic residues. However, it lacks two otherwise conserved cysteine residues near its C-terminus. Thus hNADase, the truncated protein of 207 amino acids, represents the smallest functional domain endowed with all the catalytic activities of CD38/NAD(+) glycohydrolases so far identified. Altogether, our data strongly suggest that the cloned bovine spleen ecto-NAD(+) glycohydrolase is the bovine equivalent of CD38.
牛脾胞外NAD(+)糖水解酶是哺乳动物膜相关NAD(P)(+)糖水解酶家族（EC 3.2.2.6）的典型成员，具有与CD38相似的催化特性，CD38最初被描述为一种参与环ADP-核糖代谢和信号转导的淋巴细胞分化标志物。利用从NAD(+)糖水解酶以及纯化至同质的该酶截短的水溶性形式（hNADase）获得的氨基酸序列信息，得到了一个全长cDNA克隆。推导的序列表明该蛋白有278个残基，分子量为31.5 kDa。预测牛胞外NAD(+)糖水解酶是一种II型跨膜蛋白，胞内尾巴非常短。该酶的大部分位于细胞外，含有两个潜在的N-糖基化位点，产生了截短71个残基的具有完全催化活性的hNADase。用全长cDNA转染HeLa细胞导致在细胞表面表达预期的NAD(+)糖水解酶、ADP-核糖基环化酶和GDP-核糖基环化酶活性。牛酶是第一个结构已确定的“经典”NAD(P)(+)糖水解酶，与CD38具有特别高的序列同一性，包括胞外结构域中存在10个严格保守的半胱氨酸残基和推定的催化残基。然而，它在其C末端附近缺少另外两个保守的半胱氨酸残基。因此，207个氨基酸的截短蛋白hNADase代表了迄今为止鉴定的具有CD38/NAD(+)糖水解酶所有催化活性的最小功能结构域。总之，我们的数据强烈表明克隆的牛脾胞外NAD(+)糖水解酶等同于牛的CD38。
