Zafar Sadia, Jabeen Ishrat
Research Center for Modeling and Simulation (RCMS), National University of Sciences and Technology (NUST), Islamabad, Federal, Pakistan.
PeerJ. 2019 Jan 31;7:e6283. doi: 10.7717/peerj.6283. eCollection 2019.
The γ-aminobutyric acid (GABA) transporter GAT1 is involved in GABA transport across the biological membrane in and out of the synaptic cleft. The efficiency of this Na coupled GABA transport is regulated by an electrochemical gradient, which is directed inward under normal conditions. However, in certain pathophysiological situations, including strong depolarization or an imbalance in ion homeostasis, the GABA influx into the cytoplasm is increased by re-uptake transport mechanism. This mechanism may lead to extra removal of extracellular GABA which results in numerous neurological disorders such as epilepsy. Thus, small molecule inhibitors of GABA re-uptake may enhance GABA activity at the synaptic clefts.
In the present study, various GRID-independent molecular descriptor (GRIND) models have been developed to shed light on the 3D structural features of human GAT1 (hGAT1) inhibitors using nipecotic acid and N-diarylalkenyl piperidine analogs. Further, a binding hypothesis has been developed for the selected GAT1 antagonists by molecular docking inside the binding cavity of hGAT1 homology model.
Our results indicate that two hydrogen bond acceptors, one hydrogen bond donor and one hydrophobic region at certain distances from each other play an important role in achieving high inhibitory potency against hGAT1. Our docking results elucidate the importance of the COOH group in hGAT1 antagonists by considering substitution of the COOH group with an isoxazol ring in compound , which subsequently leads to a three order of magnitude decrease in biological activity of (IC = 38 µM) as compared to compound (IC = 0.040 µM).
Our docking results are strengthened by the structure activity relationship of the data series as well as by GRIND models, thus providing a significant structural basis for understanding the binding of antagonists, which may be useful for guiding the design of hGAT1 inhibitors.
γ-氨基丁酸（GABA）转运体GAT1参与GABA跨生物膜进出突触间隙的转运。这种钠偶联的GABA转运效率受电化学梯度调节，在正常情况下该梯度向内。然而，在某些病理生理情况下，包括强烈去极化或离子稳态失衡，通过再摄取转运机制，GABA向细胞质内的流入会增加。这种机制可能导致细胞外GABA过度清除，从而引发多种神经系统疾病，如癫痫。因此，GABA再摄取的小分子抑制剂可能会增强突触间隙处的GABA活性。
在本研究中，已开发出各种独立于GRID的分子描述符（GRIND）模型，以利用尼克酸和N-二芳基烯基哌啶类似物来阐明人GAT1（hGAT1）抑制剂的三维结构特征。此外，通过在hGAT1同源模型的结合腔内进行分子对接，为所选的GAT1拮抗剂建立了结合假说。
我们的结果表明，两个氢键受体、一个氢键供体和一个彼此相距一定距离的疏水区域在实现对hGAT1的高抑制效力方面起着重要作用。我们的对接结果通过考虑化合物中用异恶唑环取代COOH基团，阐明了hGAT1拮抗剂中COOH基团的重要性，这随后导致化合物的生物活性（IC = 38 µM）与化合物（IC = 0.040 µM）相比降低了三个数量级。
我们的数据系列的构效关系以及GRIND模型加强了我们的对接结果，从而为理解拮抗剂的结合提供了重要的结构基础，这可能有助于指导hGAT1抑制剂的设计。
