Koltin Y, Faucette L, Bergsma D J, Levy M A, Cafferkey R, Koser P L, Johnson R K, Livi G P
Department of Biomolecular Discovery, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406.
Mol Cell Biol. 1991 Mar;11(3):1718-23. doi: 10.1128/mcb.11.3.1718-1723.1991.
Rapamycin is a macrolide antifungal agent with structural similarity to FK506. It exhibits potent immunosuppressive properties analogous to those of both FK506 and cyclosporin A (CsA). Unlike FK506 and CsA, however, rapamycin does not inhibit the transcription of early T-cell activation genes, including interleukin-2, but instead appears to block downstream events leading to T-cell activation. FK506 and CsA receptor proteins (FKBP and cyclophilin, respectively) have been identified and shown to be distinct members of a class of enzymes that possess peptidyl-prolyl cis-trans isomerase (PPIase) activity. Despite the apparent differences in their mode of action, rapamycin and FK506 act as reciprocal antagonists in vivo and compete for binding to FKBP. As a means of rapidly identifying a target protein for rapamycin in vivo, we selected and genetically characterized rapamycin-resistant mutants of Saccharomyces cerevisiae and isolated a yeast genomic fragment that confers drug sensitivity. We demonstrate that the resonse to rapamycin in yeast cells is mediated by a gene encoding a 114-amino-acid, approximately 13-kDa protein which has a high degree of sequence homology with human FKBP; we designated this gene RBP1 (for rapamycin-binding protein). The RBP1 protein (RBP) was expressed in Escherichia coli, purified to homogeneity, and shown to catalyze peptidyl-prolyl isomerization of a synthetic peptide substrate. PPIase activity was completely inhibited by rapamycin and FK506 but not by CsA, indicating that both macrolides bind to the recombinant protein. Expression of human FKBP in rapamycin-resistant mutants restored rapamycin sensitivity, indicating a functional equivalence between the yeast and human enzymes.
雷帕霉素是一种大环内酯类抗真菌剂，其结构与FK506相似。它具有与FK506和环孢素A（CsA）类似的强大免疫抑制特性。然而，与FK506和CsA不同的是，雷帕霉素并不抑制早期T细胞激活基因（包括白细胞介素-2）的转录，而是似乎阻断导致T细胞激活的下游事件。已经鉴定出FK506和CsA的受体蛋白（分别为FKBP和亲环蛋白），并证明它们是具有肽基脯氨酰顺反异构酶（PPIase）活性的一类酶的不同成员。尽管它们的作用方式明显不同，但雷帕霉素和FK506在体内作为相互拮抗剂起作用，并竞争与FKBP的结合。作为在体内快速鉴定雷帕霉素靶蛋白的一种方法，我们选择并对酿酒酵母的雷帕霉素抗性突变体进行了遗传表征，并分离出一个赋予药物敏感性的酵母基因组片段。我们证明酵母细胞对雷帕霉素的反应是由一个编码114个氨基酸、约13 kDa蛋白的基因介导的，该蛋白与人类FKBP具有高度的序列同源性；我们将这个基因命名为RBP1（雷帕霉素结合蛋白）。RBP1蛋白（RBP）在大肠杆菌中表达，纯化至同质，并显示出催化合成肽底物的肽基脯氨酰异构化的能力。PPIase活性被雷帕霉素和FK506完全抑制，但不被CsA抑制，这表明这两种大环内酯类药物都与重组蛋白结合。在雷帕霉素抗性突变体中表达人类FKBP可恢复雷帕霉素敏感性，这表明酵母和人类酶之间具有功能等效性。
