Molecular control of melanocortin receptor signaling

描述(申请人提供)：在大脑中，控制代谢功能和摄食行为的关键焦点是黑素皮质素受体MC3R和MC4R。这些受体对两种配体--α-黑素细胞刺激素和刺激性相关蛋白(AgRP)作出反应，这两种配体分别以相反的方式促进负能量平衡和正能量平衡。本项目的目标是了解MCR调控的分子基础。上一个资助期的工作发现了AgRP处理的新机制特征，解决了在皮肤中发现的同源刺鼠信号蛋白(ASIP)的核磁共振结构，并确定由免疫系统释放的2-防御素是一类新的MCR配体。这项研究的下一阶段将以这些进展为基础，开展以下四个项目。1)AgRP N-末端结构域显著抑制其与MCRs的亲和力。核磁共振、药理学和体内协作研究将被用来检验这样的假设，即部分保守的酸性结构域与C末端环对接，从而阻断受体对接。2)2-防御素与AgRP或ASIP不是同源的，但对它们各自的结构特征的比较发现了可能靶向MCR的特定环。结构-功能研究将揭示2-防御素拮抗MCRs的结构基础。3)虽然已发表的工作确定2-防御素3是MC1R和MC4R的配体，但初步结果表明其他防御素也与其结合。将对2-防御素家族进行筛查，以确定其他MCR相互作用，从而指出潜在的新的2-防御素功能。4)2-防御素在体外很难折叠，从而混淆了重要的功能研究。人类ASIP出现了类似的困难，PI的实验室使用蛋白质工程克服了这些困难。类似的策略将用于2-防御素家族的成员，以促进对防御素折叠的理解，并产生用于药理学和结构研究的有用蛋白质。与公共健康相关：肥胖是西方社会面临的最大公共健康问题之一。这种情况源于能量摄入和消耗之间的失衡，并导致糖尿病、高血压、高胆固醇、冠状动脉疾病、胆囊病、某些癌症和骨关节炎。在大脑中，黑素皮质素系统在控制摄食行为和代谢功能方面发挥着核心作用。黑素皮质素受体被认为是主要的治疗靶点。这项研究计划利用蛋白质结构测定、蛋白质工程、药理学和筛选来揭示负责调节黑素皮质素系统的分子细节。

DESCRIPTION (provided by applicant): In the brain, key focal points for control of metabolic function and feeding behavior are melanocortin receptors MC3R and MC4R. These receptors respond to two ligands, alpha-melanocyte stimulating hormone and Agouti-related protein (AgRP), which act in opposite ways to promote negative and positive energy balance, respectively. The goal of this program is to understand the molecular basis of MCR regulation. Work from the last funding period uncovered new mechanistic features of AgRP processing, solved the NMR structure of the homologous agouti signaling protein (ASIP) found in the skin, and identified 2-defensins, released by the immune system, as a new class of MCR ligands. The next phase of this research will build on these advances with the following four projects. 1) The AgRP N-terminal domain greatly inhibits its affinity for MCRs. NMR, pharmacology and collaborative in vivo studies, will be used to test the hypothesis that a partially conserved acidic domain docks to a C-terminal loop thus occluding receptor docking. 2) 2-Defensins are not homologous to AgRP or ASIP, but comparison of their respective structural features identifies specific loops that may target MCRs. Structure- function studies will uncover the structural basis for 2-defensin antagonism of MCRs. 3) Although published work identifies 2-defensin 3 as a ligand to MC1R and MC4R, preliminary results show that other defensins bind as well. A screen across the family of 2-defensins will be performed to identify additional MCR interactions, thus pointing to potential new 2-defensin functions. 4) 2-Defensins are challenging to fold in vitro, thus confounding important functional investigations. Human ASIP presented similar difficulties that were overcome by the PI's lab using protein engineering. Analogous strategies will be used with members of the 2-defensin family to advance the understanding of the defensin fold and to produce useful protein for pharmacological and structural studies. PUBLIC HEALTH RELEVANCE: Obesity is one of the greatest public health concerns facing Western society. The condition arises from an imbalance between energy intake and expenditure and contributes to diabetes, high blood pressure, high blood cholesterol, coronary artery disease, gallbladder disease, certain cancers and osteoarthritis. In the brain, the melanocortin system plays a central role in controlling feeding behavior and metabolic function. Melanocortin receptors are identified as prime therapeutic targets. This research program uses protein structure determination, protein engineering, pharmacology and screening to uncover the molecular details responsible for regulation of the melanocortin system.