Miyamoto K, Katai K, Tatsumi S, Sone K, Segawa H, Yamamoto H, Taketani Y, Takada K, Morita K, Kanayama H
Department of Clinical Nutrition, School of Medicine, Tokushima University, Japan.
Biochem J. 1995 Sep 15;310 ( Pt 3)(Pt 3):951-5. doi: 10.1042/bj3100951.
To investigate the function of a basic and neutral amino acid transporter-like protein (rBAT) which is a candidate gene for cystinuria, we analysed the rBAT gene in cystinuric patients. Patient 1 is a compound heterozygote with mutations in the rBAT gene causing a glutamine-to-lysine transition at amino acid 268, and a threonine-to-alanine transition at amino acid 341, who inherited these alleles from his mother (E268K) and father (T341A), respectively. Injection of T341A and E268K mutant cRNAs into oocytes decreased transport activity to 53.9% and 62.5% of control (L-cystine transport activity in oocytes injected with wild-type rBAT cRNA), respectively. Co-injection of E268K and T341A into oocytes strongly decreased amino acid transport activity to 28% of control. On the other hand, co-injection of wild-type and mutant rBAT did not decrease transport activity. Furthermore, immunological studies have demonstrated that the reduction of amino acid transport is not due to a decrease in the amount of rBAT protein expressed in oocyte membranes. These results indicate that mutations in the rBAT gene are crucial disease-causing lesions in cystinuria. In addition, co-injection experiments suggest that rBAT may function as a transport activator or regulatory subunit by homo- or hetero-multimer complex formation.
为了研究一种碱性和中性氨基酸转运体样蛋白（rBAT）的功能，该蛋白是胱氨酸尿症的候选基因，我们分析了胱氨酸尿症患者的rBAT基因。患者1是rBAT基因的复合杂合子，在该基因中存在突变，导致第268位氨基酸由谷氨酰胺转变为赖氨酸，第341位氨基酸由苏氨酸转变为丙氨酸，他分别从母亲（E268K）和父亲（T341A）那里继承了这些等位基因。将T341A和E268K突变型cRNA注射到卵母细胞中后，转运活性分别降至对照（注射野生型rBAT cRNA的卵母细胞中的L-胱氨酸转运活性）的53.9%和62.5%。将E268K和T341A共同注射到卵母细胞中会使氨基酸转运活性大幅下降至对照的28%。另一方面，将野生型和突变型rBAT共同注射不会降低转运活性。此外，免疫学研究表明，氨基酸转运的降低并非由于卵母细胞膜中表达的rBAT蛋白量减少所致。这些结果表明，rBAT基因中的突变是胱氨酸尿症的关键致病损伤。此外，共同注射实验表明，rBAT可能通过形成同源或异源多聚体复合物而作为转运激活剂或调节亚基发挥作用。
