Paton B C, Schmid B, Kustermann-Kuhn B, Poulos A, Harzer K
Department of Chemical Pathology, Adelaide Medical Centre for Women and Children, Australia.
Biochem J. 1992 Jul 15;285 ( Pt 2)(Pt 2):481-8. doi: 10.1042/bj2850481.
It has been shown that sphingolipid activator proteins (SAPs) 1 and 2 are encoded on the same gene along with two other putative activator proteins [Fürst, Machleidt & Sandhoff (1988) Biol. Chem. Hoppe-Seyler 369, 317-328 and O'Brien, Kretz, Dewji, Wenger, Esch & Fluharty (1988) Science 241, 1098-1101]. We have undertaken further biochemical investigations on a patient and fetal sibling, who were previously shown to have a unique sphingolipid storage disorder associated with an SAP-2 deficiency [Harzer, Paton, Poulos, Kustermann-Kuhn, Roggendorf, Grisar & Popp (1989) Eur. J. Pediatr. 149, 31-39]. The severity of their disorder suggested that other products of the SAP precursor or prosaposin gene may also be deficient. The turnover of cerebroside sulphate and globotriaosylceramide were investigated and were both impaired in fibroblasts from the patient and fetus. However, the activities of cerebroside sulphate sulphatase and globotriaosylceramide alpha-galactosidase in vitro were normal in cells from the fetus and patient respectively. In addition, there was an increase in cerebroside sulphate concentration in the kidney of the affected fetus. These results indicate that, in addition to the SAP-2 deficiency, there was a defect in SAP-1 function in this disorder. Additional increases in the concentration of monohexosyl- and dihexosyl-ceramide in the fetal kidney probably reflect the deficiency of SAP-2 in the case of monohexosylceramides, and the combined activator deficiency in the case of dihexosylceramides. Lactosylceramide-loading studies confirmed that there was a defect in the turnover of this lipid in fibroblasts from the affected patient and fetus but not from a patient with an isolated SAP-1 deficiency, or from patients with Krabbe disease, GM1 gangliosidosis or galactosialidosis. It has been suggested [Potier, Lamontagne, Michaud & Tranchemontagne (1990) Biochem. Biophys. Res. Commun. 173, 449-456] that the prosaposin gene also codes for lysosomal neuroaminidase. However, we found normal neuraminidase activity in fibroblasts from our patient, using assay conditions which are diagnostic for sialidosis patients. The role of prosaposin gene products in sphingolipid metabolism is discussed in view of our biochemical findings in this genetic disorder.
已表明鞘脂激活蛋白（SAPs）1和2与其他两种假定的激活蛋白一起在同一基因上编码[Fürst、Machleidt和Sandhoff（1988年），《生物化学.霍普 - 赛勒》369卷，317 - 328页；以及O'Brien、Kretz、Dewji、Wenger、Esch和Fluharty（1988年），《科学》241卷，1098 - 1101页]。我们对一名患者及其胎儿同胞进行了进一步的生化研究，他们之前被证明患有与SAP - 2缺乏相关的独特鞘脂贮积症[Harzer、Paton、Poulos、Kustermann - Kuhn、Roggendorf、Grisar和Popp（1989年），《欧洲儿科杂志》149卷，31 - 39页]。他们病症的严重程度表明，SAP前体或prosaposin基因的其他产物可能也存在缺陷。对脑硫脂和球三糖基神经酰胺的周转进行了研究，发现患者和胎儿的成纤维细胞中这两种物质的周转均受损。然而，胎儿和成纤维细胞中脑硫脂硫酸酯酶和球三糖基神经酰胺α - 半乳糖苷酶的体外活性分别正常。此外，患病胎儿的肾脏中脑硫脂浓度有所增加。这些结果表明，除了SAP - 2缺乏外，该病症中SAP - 1功能也存在缺陷。胎儿肾脏中单己糖基神经酰胺和二己糖基神经酰胺浓度的额外增加，可能分别反映了单己糖基神经酰胺情况下SAP - 2的缺乏，以及二己糖基神经酰胺情况下激活蛋白的联合缺乏。乳糖基神经酰胺负载研究证实，患病患者和胎儿的成纤维细胞中这种脂质的周转存在缺陷，但孤立性SAP - 1缺乏患者、克拉贝病患者、GM1神经节苷脂贮积症患者或半乳糖唾液酸贮积症患者的成纤维细胞中不存在这种缺陷。有人提出[Potier、Lamontagne、Michaud和Tranchemontagne（1990年），《生物化学与生物物理研究通讯》173卷，449 - 456页]，prosaposin基因也编码溶酶体神经氨酸酶。然而，我们在患者的成纤维细胞中发现神经氨酸酶活性正常，所采用的检测条件对唾液酸贮积症患者具有诊断意义。鉴于我们在这种遗传性疾病中的生化发现，讨论了prosaposin基因产物在鞘脂代谢中的作用。
