Molecular Characterization of Hepatic Organic Anion Transporting Polypeptides

描述(申请人提供)：有机阴离子转运多肽OATP1B1和OATP1B3是人肝细胞表达的两种主要药物转运蛋白。由于它们的多重特异性，这两种转运体是药物相互作用的潜在部位。在之前的赠款期间，我们表征了底物依赖的调制，确定了底物结合位点的分子特征，并确定了几个对OATP1B1和OATP1B3介导的底物转运重要的氨基酸残基。然而，导致其多特异性的分子机制仍不清楚。我们的长期研究目标是详细了解OATP介导的转运机制，作为了解、预测和预防OATP相关不良药物相互作用的必要前提。提出这项研究的理由是，因为OATP1B1和OATP1B3与肝脏清除血液中多种化学物质的能力密切相关，对它们各自和重叠的转运蛋白功能的更好的机械性洞察将为改进预测和预防药物与药物的不良相互作用以及未来设计特定底物和/或其转运活动的抑制剂提供强有力的科学框架。这项应用的目的是确定对底物转运和刺激至关重要的结构域和氨基酸，并表征运输的驱动力(S)。我们的中心假设是OATP1B1和OATP1B3通过包括底物特异性转位途径的中央孔道运输底物，OATP1B1和OATP1B3作为不对称的交换器工作。我们计划用两个具体的目标来检验这一假说：1)鉴定和表征OATP1B1和OATP1B3的转位途径；2)确定OATP介导的转运机制。这些特定目标的完成将通过识别不同跨膜区中影响底物转运的氨基酸来解释底物依赖效应，并将使我们更接近这些膜转运蛋白的三维结构。此外，我们将解决转运机制的争议，确定一个生理的反阴离子，并解释可能由转运体的低聚状态引起的变构效应。这一贡献意义重大，因为它的结果将为预测OATP介导的药物转运提供所需的基本理解，最终导致除了从根本上推进有机阴离子转运领域之外，更有效和高效的治疗方法。

DESCRIPTION (provided by applicant): The organic anion transporting polypeptides OATP1B1 and OATP1B3 are two major drug transporters expressed in human hepatocytes. Because of their multispecificity, these two transporters are potential sites of adverse drug-drug interactions. In the previous grant period, we characterized substrate dependent modulation, identified molecular characteristics of the substrate binding sites, and identified several amino acid residues important for OATP1B1- and OATP1B3-mediated substrate transport. However, the molecular mechanisms responsible for their multispecificities remain unclear. Our long term research goal is to understand in detail the mechanism of OATP-mediated transport as an essential prerequisite to understanding, predicting, and preventing OATP-related adverse drug-drug interactions. The rationale for the proposed research is that, because OATP1B1 and OATP1B3 are critically involved in the liver's ability to clear numerous chemicals from the blood, improved mechanistic insights into their individual and overlapping transporter functions will provide a strong scientific framework for improvements in the prediction and prevention of adverse drug-drug interactions, as well as the future design of specific substrates and/or inhibitors of their transport activity. The objective of this application is to identify domains and amino acids that are important for substrate translocation and stimulation, and to characterize the driving force(s) for transport. Our central hypothesis is that OATP1B1 and OATP1B3 transport their substrates via a central pore that includes substrate-specific translocation pathways, and that OATP1B1 and OATP1B3 work as asymmetrical exchangers. We plan to test the hypothesis with two specific aims: 1) Identify and characterize the translocation pathways of OATP1B1 and OATP1B3; and 2) Determine the mechanism of OATP-mediated transport. Completion of these specific aims will explain the substrate dependent effects by identifying amino acids in the different transmembrane domains that influence substrate translocation and will lead us a step closer to the three dimensional structure of these membrane transporters. Furthermore, we will resolve the controversies of the transport mechanism, identify a physiological counter-anion, and explain the allosteric effects that might be due to the oligomeric state of the transporters. This contribution is significant because its results will provide the fundamental understanding required to predict OATP- mediated drug transport, ultimately leading to more effective and efficient therapies in addition to fundamentally advancing the field of organic anion transport.