Correa V, Riley A M, Shuto S, Horne G, Nerou E P, Marwood R D, Potter B V, Taylor C W
Department of Pharmacology, University of Cambridge, Cambridge, CB2 1QJ, United Kingdom.
Mol Pharmacol. 2001 May;59(5):1206-15. doi: 10.1124/mol.59.5.1206.
Adenophostin A is the most potent known agonist of inositol 1,4,5-trisphosphate (InsP(3)) receptors. Ca(2+) release from permeabilized hepatocytes was 9.9 +/- 1.6-fold more sensitive to adenophostin A (EC(50), 14.7 +/- 2.4 nM) than to InsP(3) (145 +/- 10 nM), consistent with the greater affinity of adenophostin A for hepatic InsP(3) receptors (K(d) = 0.48 +/- 0.06 and 3.09 +/- 0.33 nM, respectively). Here, we systematically modify the structures of the glucose, ribose, and adenine moieties of adenophostin A and use Ca(2+) release and binding assays to define their contributions to high-affinity binding. Progressive trimming of the adenine of adenophostin A reduced potency, but it fell below that of InsP(3) only after complete removal of the adenine. Even after substantial modifications of the adenine (to uracil or even unrelated aromatic rings, retaining the beta-orientation), the analogs were more potent than InsP(3). The only analog with an alpha-ribosyl linkage had massively decreased potency. The 2'-phosphate on the ribose ring of adenophostin A was essential and optimally active when present on a five-membered ring in a position stereochemically equivalent to its location in adenophostin A. Xylo-adenophostin, where xylose replaces the glucose ring of adenophostin A, was only slightly less potent than adenophostin A, whereas manno-adenophostin (mannose replacing glucose) had similar potency to InsP(3). These results are consistent with the relatively minor role of the 3-hydroxyl of InsP(3) (the equivalent is absent from xylo-adenophostin) and greater role of the equatorial 6-hydroxyl (the equivalent is axial in manno-adenophostin). This is the first comprehensive analysis of all the key structural elements of adenophostin A, and it provides a working model for the design of related high-affinity ligands of InsP(3) receptors.
腺嘌呤宿主素A是已知对肌醇1,4,5 -三磷酸（InsP(3)）受体最具活性的激动剂。与InsP(3)（145±10 nM）相比，通透化肝细胞中Ca(2+)的释放对腺嘌呤宿主素A（EC(50)，14.7±2.4 nM）的敏感性高9.9±1.6倍，这与腺嘌呤宿主素A对肝脏InsP(3)受体具有更高亲和力一致（K(d)分别为0.48±0.06和3.09±0.33 nM）。在此，我们系统地修饰了腺嘌呤宿主素A的葡萄糖、核糖和腺嘌呤部分的结构，并使用Ca(2+)释放和结合测定来确定它们对高亲和力结合的贡献。对腺嘌呤宿主素A的腺嘌呤进行逐步修剪会降低其活性，但只有在完全去除腺嘌呤后才会降至InsP(3)以下。即使对腺嘌呤进行了大量修饰（变为尿嘧啶甚至不相关的芳香环，保持β-取向），类似物的活性仍高于InsP(3)。唯一具有α-核糖基连接的类似物活性大幅降低。腺嘌呤宿主素A核糖环上的2'-磷酸至关重要，当存在于五元环中与腺嘌呤宿主素A中位置立体化学等效的位置时具有最佳活性。木糖-腺嘌呤宿主素（木糖取代腺嘌呤宿主素A的葡萄糖环）的活性仅略低于腺嘌呤宿主素A，而甘露糖-腺嘌呤宿主素（甘露糖取代葡萄糖）的活性与InsP(3)相似。这些结果与InsP(3)的3-羟基（木糖-腺嘌呤宿主素中不存在等效物）作用相对较小以及赤道面6-羟基（甘露糖-腺嘌呤宿主素中该等效物为轴向）作用较大一致。这是对腺嘌呤宿主素A所有关键结构元件的首次全面分析，为设计InsP(3)受体相关高亲和力配体提供了一个工作模型。
