Defining Substrate and Blocker Activity of Alanine-Serine-Cysteine Transporter 2 (ASCT2) Ligands with Novel Serine Analogs
作者:Thomas Albers、William Marsiglia、Taniya Thomas、Armanda Gameiro、Christof Grewer
DOI:10.1124/mol.111.075648
日期:2012.3
The neutral amino acid transporter alanine-serine-cysteine transporter 2 (ASCT2) belongs to the solute carrier 1 (SLC1) family of solute transporters and transports small, neutral amino acids across the membrane, including the physiologically important and ubiquitous amino acid glutamine. Our understanding of the involvement of ASCT2 in the physiological processes involving glutamine is hampered by a lack of understanding of its pharmacology and the absence of high-affinity inhibitors. In this study, we combined an in silico docking approach with experimental investigation of binding parameters to develop new ASCT2 inhibitors and substrates, a series of serine esters, and to determine structural parameters that govern their functional effects. The series of compounds was synthesized using standard methods and exhibited a range of properties, from inhibitors to partial substrates and full substrates. Our results suggest that amino acid derivatives with small side-chain volume and low side-chain hydrophobicity interact strongly with the closed-loop form of the binding site, in which re-entrant loop 2, the presumed extracellular gate for the substrate binding site, is closed off. However, these derivatives bind weakly to the open-loop form (external gate open to the extracellular side), acting as transported substrates. In contrast, inhibitors bind preferentially to the open-loop form. An aromatic residue in the side chain is required for high-affinity interaction. One of the compounds, the l-serine ester serine biphenyl-4-carboxylate reversibly inhibits ASCT2 function with an apparent affinity of 30 μM.
中性氨基酸转运蛋白丙氨酸-丝氨酸-半胱氨酸转运蛋白 2 (ASCT2) 属于溶质转运蛋白的溶质载体 1 (SLC1) 家族,可跨膜转运小型中性氨基酸,包括生理上重要且普遍存在的氨基酸谷氨酰胺。由于缺乏对其药理学的了解以及缺乏高亲和力抑制剂,我们对 ASCT2 参与谷氨酰胺生理过程的理解受到阻碍。在这项研究中,我们将计算机对接方法与结合参数的实验研究相结合,开发新的 ASCT2 抑制剂和底物、一系列丝氨酸酯,并确定控制其功能效果的结构参数。该系列化合物是使用标准方法合成的,并表现出从抑制剂到部分底物和完整底物的一系列特性。我们的结果表明,具有小侧链体积和低侧链疏水性的氨基酸衍生物与结合位点的闭环形式强烈相互作用,其中重入环2(推测的底物结合位点的细胞外门)已关闭。然而,这些衍生物与开环形式(外门向细胞外侧开放)的结合较弱,充当运输底物。相反,抑制剂优先结合开环形式。侧链中的芳香族残基是高亲和力相互作用所必需的。其中一种化合物 L-丝氨酸酯丝氨酸联苯-4-羧酸酯可逆地抑制 ASCT2 功能,表观亲和力为 30 μM。