Jackson Pilgrim J, Yu Bin, Hunrichs Benjamin, Thompson Darren A, Chai Biaoxin, Gantz Ira, Millhauser Glenn L
Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064, USA.
Peptides. 2005 Oct;26(10):1978-87. doi: 10.1016/j.peptides.2004.12.036.
The specific melanocortin receptors, MC3R and MC4R, are directly linked to metabolism and body weight control. These receptors are activated by the peptide hormone alpha-MSH and antagonized by the agouti-related protein (AGRP). Whereas alpha-MSH acts broadly on most members of the MCR family (with the exception of MC2R), AGRP is highly specific for only MC3R and MC4R. AGRP is a complex ligand of approximately 100 amino acids. Within AGRP, MCR recognition and antagonism is localized to a 34 residue, cysteine-rich domain that adopts an inhibitor cystine knot (ICK) fold. An oxidatively folded peptide corresponding to this domain, referred to as mini-AGRP, exhibits full antagonist function and selectivity for MC3R and MC4R. Here we investigate a series of chimera proteins based on the mini-AGRP scaffold. Amino acid sequences derived from peptide agonists are grafted into the mini-AGRP active loop, implicated in receptor recognition, with the goal of producing ICK based agonists specific for MC3R and MC4R. Several constructs indeed exhibited potent agonist activity; however, with all chimeras, receptor selectivity is significantly altered. Pharmacologic data indicate that the chimeras do not interact with MC receptors through native AGRP like contacts. A model to explain the data suggest that there is only partial overlap of the agonist versus antagonist binding surfaces within MC receptors. Moreover, accessibility to the binding pocket is highly receptor specific with MC3R being the least tolerant of ligand alterations.
特定的黑皮质素受体MC3R和MC4R与新陈代谢及体重控制直接相关。这些受体由肽激素α-MSH激活，并被刺鼠相关蛋白（AGRP）拮抗。α-MSH广泛作用于大多数MCR家族成员（MC2R除外），而AGRP仅对MC3R和MC4R具有高度特异性。AGRP是一种约含100个氨基酸的复杂配体。在AGRP中，MCR识别和拮抗作用定位于一个34个残基的富含半胱氨酸的结构域，该结构域采用抑制剂胱氨酸结（ICK）折叠。对应于该结构域的氧化折叠肽，称为微型AGRP，对MC3R和MC4R表现出完全的拮抗功能和选择性。在此，我们基于微型AGRP支架研究了一系列嵌合蛋白。将源自肽激动剂的氨基酸序列嫁接到与受体识别有关的微型AGRP活性环中，目的是产生对MC3R和MC4R具有特异性的基于ICK的激动剂。几种构建体确实表现出强效激动剂活性；然而，对于所有嵌合体，受体选择性都发生了显著改变。药理学数据表明，嵌合体与MC受体的相互作用并非通过天然AGRP样接触。一个解释该数据的模型表明，MC受体内激动剂与拮抗剂结合表面仅部分重叠。此外，结合口袋的可及性具有高度受体特异性，MC3R对配体改变的耐受性最低。
