Water soluble variants of the human mu opioid receptor

说明(申请人提供)：阿片类药物仍然是围术期和慢性疼痛治疗的主要药物，尽管它们有副作用，包括呼吸抑制、便秘、成瘾和其他与我们患者的发病率和死亡率相关的副作用，以及带来重大的经济和政治负担。由于镇痛和副作用都被认为是由受体(MUR)的激活引起的，因此更好地了解人类MUR的结构和功能关系将为解决这一临床难题提供线索。在这个项目中，我们将基于小鼠MUR的新晶体结构设计人MU受体的水溶变体(WsMUR)，研究该受体在N和C末端存在或不存在的情况下的性质，并建立一种不需要放射性配体或哺乳动物细胞来研究阿片配体与受体直接相互作用的系统。本研究的主要目的有两个。在具体目标1中，我们将根据小鼠MUR的晶体结构和我们最近发表的第一版工程受体，设计和研究新一代wsMUR，并利用wsMUR和表面等离子体共振的优势，建立一种新的研究阿片类药物与受体直接相互作用的系统。在具体目标2中，我们将通过改变跨膜区广泛的表面残基来计算设计wsMURs的变体，以检验以下假设：1)对使人MUR能够在大肠杆菌中表达的突变数量有最低要求，具有合理的水溶性和与其天然形式类似的性质~2)基于我们过去对膜蛋白的蛋白质工程经验，受体可以容忍跨膜部分残基的35%的突变，以最大限度地增加水的溶解性并改善单体状态，以便在未来的高分辨率蛋白质动力学研究(即核磁共振)中在溶液条件下去除半胱氨酸在受体表面的跨膜部分可以减少二硫键诱导的蛋白质二聚化。该项目不仅为结构功能关系研究提供了wsMUR的各种变体，而且还产生了一种新的系统，可以研究阿片类药物与MUR之间的直接相互作用，并提供了重大的技术突破。因此，本项目旨在阐明MUR的分子机制，并帮助识别副作用减少的新型阿片类止痛药，改善疼痛控制，并解决与阿片类药物给药和滥用相关的问题。该小组在设计水溶膜蛋白方面有过往记录。化学系的萨文教授是蛋白质工程专家，麻醉学系的刘教授是阿片受体专家。所有具体目标的初步数据都很有希望。

DESCRIPTION (provided by applicant): Opioids remain the major medication for perioperative and chronic pain management despite their side effects, which include respiratory depression, constipation, addiction and others related to morbidity and mortality in our patients, as well as presenting a significant economic and political burden. Since both the analgesic and side effects are thought to arise from activation of the ¿-receptor (MUR), a better understanding of the structural and functional relationships of human MUR will provide clues in addressing this clinical dilemma. In this project, we will engineer water soluble variants of the human mu receptor (wsMUR) based on the newly available crystal structure of murine MUR, investigate the properties of the receptor in the presence or absence of N and C terminus, and establish a system in investigating the direct interaction of an opioid ligand with the receptor without needing radioactive ligands or mammalian cells. There are 2 major aims for this study. In specific aim 1, we will engineer and study a new generation of wsMUR based on the crystal structure of murine MUR along with our first version of engineered receptor published recently and establish a novel system in investigating the direct interaction of opioid and receptor by taking the advantages of wsMUR and surface plasmon resonance. In specific aim 2, we will computationally engineer variants of wsMURs by changing wide ranges of surface residues in the transmembrane region to test the following hypotheses: 1) There is a minimal requirement of the number of mutations enabling the human MUR to be expressed in E coli with a reasonable water solubility and comparable properties to its native form~ 2) The receptor may tolerate 35% of the mutations for the residues in the transmembrane portion based on our past experiences of protein engineering on the membrane proteins to maximize water solubility and improve monomeric states for future high resolution protein dynamics studies (i.e. nuclear magnetic resonance) in solution conditions~ 3) Removal of cysteine on the surface of the transmembrane portion of the receptor could reduce disulfide bond induced protein dimerization. This project not only provides various variants of wsMUR for structure function relationship studies, but also yields a novel system that can investigate the direct interaction between opioids and MUR, and offer a significant technology breakthrough. Thus, this project stands to elucidate the molecular mechanisms of MUR and aid in the identification of novel opioid analgesics with reduced side effects, improved pain control, and address issues related to opioid administration and abuse. This group has a track record in engineering water soluble membrane proteins. Professor Saven at the Department of Chemistry is an expert on protein engineering and Professor Liu at the Department of Anesthesiology is an expert on opioid receptors. The preliminary data for all the specific aims are promising.