Molecular control of melanocortin receptor signaling

描述（由申请人提供）：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。这些受体响应两种配体，α -黑色素细胞刺激激素和agouti相关蛋白（AgRP），它们以相反的方式分别促进负能量和正能量平衡。该计划的目标是了解MCR调控的分子基础。上一个资助期的工作揭示了AgRP加工的新机制特征，解决了在皮肤中发现的同源agouti信号蛋白（ASIP）的NMR结构，并鉴定了由免疫系统释放的2-防御素作为一类新的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端结构域极大地抑制了其对mcr的亲和力。核磁共振、药理学和协作体内研究将用于测试部分保守的酸性结构域与c端环对接从而阻断受体对接的假设。2) 2-防御素与AgRP或ASIP并不同源，但通过比较它们各自的结构特征，可以识别出可能针对mcr的特定环。结构-功能研究将揭示mcr抗2-防御素的结构基础。3)虽然已发表的研究确定2-防御蛋白3是MC1R和MC4R的配体，但初步结果表明其他防御蛋白也可以结合。将对2-防御素家族进行筛选，以确定额外的MCR相互作用，从而指出潜在的新2-防御素功能。4) 2-防御素在体外折叠具有挑战性，因此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-防御蛋白家族的成员，以促进对防御蛋白折叠的理解，并为药理学和结构研究产生有用的蛋白质。

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.