Molecular Characterization of Hepatic Organic Anion Transporting Polypeptides

描述（由申请方提供）：有机阴离子转运多肽OATP 1B 1和OATP 1B 3是人肝细胞中表达的两种主要药物转运蛋白。由于它们的多特异性，这两种转运蛋白是潜在的不良药物-药物相互作用的位点。在上一个资助期，我们表征了底物依赖性调节，鉴定了底物结合位点的分子特征，并鉴定了对OATP 1B 1和OATP 1B 3介导的底物转运重要的几个氨基酸残基。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，这是理解、预测和预防OATP相关不良药物相互作用的必要前提。拟议研究的基本原理是，由于OATP 1B 1和OATP 1B 3与肝脏从血液中清除多种化学物质的能力密切相关，因此对其个体和重叠转运蛋白功能的机制见解的改进将为改善药物不良相互作用的预测和预防提供强有力的科学框架。以及未来设计特定底物和/或其转运活性的抑制剂。本申请的目的是鉴定对底物转运和刺激重要的结构域和氨基酸，并表征转运的驱动力。我们的中心假设是OATP 1B 1和OATP 1B 3通过一个中心孔（包括底物特异性转运途径）转运其底物，并且OATP 1B 1和OATP 1B 3作为不对称交换剂发挥作用。我们计划通过两个特定目的来检验该假设：1）鉴定和表征OATP 1B 1和OATP 1B 3的易位途径; 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影响底物转运的不同跨膜结构域中的氨基酸来解释底物依赖性效应，并将使我们更接近这些膜转运蛋白的三维结构。此外，我们将解决运输机制的争议，确定一个生理抗衡阴离子，并解释变构效应，可能是由于低聚状态的转运。这一贡献是重要的，因为其结果将提供预测OATP介导的药物转运所需的基本理解，最终导致更有效和高效的治疗，以及从根本上推进有机阴离子转运领域。

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.