Davidson B L, Pashmforoush M, Kelley W N, Palella T D
Department of Internal Medicine, University of Michigan Medical School, Ann Arbor 48109.
Gene. 1988 Mar 31;63(2):331-6. doi: 10.1016/0378-1119(88)90536-7.
The molecular basis for complete hypoxanthine guanine phosphoribosyltransferase (HPRT) deficiency has been determined in a patient with Lesch-Nyhan syndrome. A B-lymphoblastoid cell line derived from this patient expresses normal amounts of HPRT mRNA yet no detectable immunoreactive protein as determined by radioimmunoassay. These findings suggest either a decreased rate of translation or accelerated degradation due to enhanced proteolytic susceptibility. cDNAs synthesized from this patient's RNA have a single nucleotide (nt) substitution, a C----A transversion at nt 222. RNase A cleavage analysis confirms the presence of a mutation at this position within mRNA isolated from lymphoblasts from patient A.C. This transversion predicts a phenylalanine to leucine replacement at amino acid position 73 in the translated protein. We have designated this mutant HPRTFlint. The mutation in HPRTFlint disrupts a strongly conserved region among PRTases from Escherichia coli, rodents and man, suggesting an important role for this region for the normal function of HPRT. Since it is unlikely that this amino acid substitution alters the translational rate, we hypothesize that disruption of the secondary structure within this region renders HPRTFlint more susceptible to proteolysis.
已在一名莱施-奈恩综合征患者中确定了完全性次黄嘌呤鸟嘌呤磷酸核糖转移酶（HPRT）缺乏的分子基础。从该患者获得的B淋巴母细胞系表达正常量的HPRT mRNA，但通过放射免疫测定法未检测到可检测的免疫反应性蛋白。这些发现表明，要么是翻译速率降低，要么是由于蛋白水解敏感性增强导致降解加速。从该患者的RNA合成的cDNA有一个单核苷酸（nt）取代，即nt 222处的C到A颠换。核糖核酸酶A切割分析证实，在从患者A.C.的淋巴母细胞分离的mRNA中该位置存在突变。这种颠换预测在翻译后的蛋白质中第73位氨基酸处苯丙氨酸被亮氨酸取代。我们将这种突变体命名为HPRTFlint。HPRTFlint中的突变破坏了大肠杆菌、啮齿动物和人类PRT酶之间一个高度保守的区域，表明该区域对HPRT的正常功能具有重要作用。由于这种氨基酸取代不太可能改变翻译速率，我们推测该区域二级结构的破坏使HPRTFlint更容易被蛋白水解。
