Department of Chemical Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany.
J Am Chem Soc. 2012 May 2;134(17):7384-91. doi: 10.1021/ja211305j. Epub 2012 Apr 22.
Post-translational attachment of geranylgeranyl isoprenoids to Rab GTPases, the key organizers of intracellular vesicular transport, is essential for their function. Rab geranylgeranyl transferase (RabGGTase) is responsible for prenylation of Rab proteins. Recently, RabGGTase inhibitors have been proposed to be potential therapeutics for treatment of cancer and osteoporosis. However, the development of RabGGTase selective inhibitors is complicated by its structural and functional similarity to other protein prenyltransferases. Herein we report identification of the natural product psoromic acid (PA) that potently and selectively inhibits RabGGTase with an IC(50) of 1.3 μM. Structure-activity relationship analysis suggested a minimal structure involving the depsidone core with a 3-hydroxyl and 4-aldehyde motif for binding to RabGGTase. Analysis of the crystal structure of the RabGGTase:PA complex revealed that PA forms largely hydrophobic interactions with the isoprenoid binding site of RabGGTase and that it attaches covalently to the N-terminus of the α subunit. We found that in contrast to other protein prenyltransferases, RabGGTase is autoinhibited through N-terminal (α)His2 coordination with the catalytic zinc ion. Mutation of (α)His dramatically enhances the reaction rate, indicating that the activity of RabGGTase is likely regulated in vivo. The covalent binding of PA to the N-terminus of the RabGGTase α subunit seems to potentiate its interaction with the active site and explains the selectivity of PA for RabGGTase. Therefore, psoromic acid provides a new starting point for the development of selective RabGGTase inhibitors.
异戊烯基焦磷酸酯与 Rab GTP 酶的翻译后附着，后者是细胞内囊泡运输的关键组织者，对于它们的功能至关重要。Rab 异戊烯基转移酶（RabGGTase）负责 Rab 蛋白的异戊烯化。最近，RabGGTase 抑制剂被提议作为治疗癌症和骨质疏松症的潜在疗法。然而，由于其与其他蛋白质prenyltransferase 的结构和功能相似，因此开发 RabGGTase 选择性抑制剂变得复杂。本文报道了天然产物 psoromic acid（PA）的鉴定，该物质能够强烈且选择性地抑制 RabGGTase，IC50 为 1.3 μM。结构-活性关系分析表明，最小的结构涉及包含 depsidone 核心的结构，具有 3-羟基和 4-醛基的 motif 用于与 RabGGTase 结合。对 RabGGTase：PA 复合物的晶体结构分析表明，PA 与 RabGGTase 的异戊烯结合位点形成主要的疏水相互作用，并且它与α亚基的 N 端共价结合。我们发现，与其他蛋白质 prenyltransferase 不同，RabGGTase 通过 N 端（α）His2 与催化锌离子的配位来自我抑制。（α）His 的突变极大地增强了反应速率，表明 RabGGTase 的活性可能在体内受到调节。PA 与 RabGGTase α亚基的 N 端的共价结合似乎增强了其与活性位点的相互作用，并解释了 PA 对 RabGGTase 的选择性。因此，psoromic acid 为开发选择性 RabGGTase 抑制剂提供了新的起点。
