The Nociceptin/orphanin FQ peptide (NOP) receptor is considered a member of the opioid receptor subfamily of G-protein coupled receptors (GPCRs) which has been shown to be present in many parts of the central nervous system (CNS). It plays biologically diverse roles in pain modulation, immune response and in neurodegenerative diseases. In this work, phytochemical conjugates of two known neuropeptides, melanocyte inhibition factor (MiF-1) and mammalian amidated neuropeptide NPFF with pain modulating ability were developed. The binding interactions of those conjugates with NOP receptor was examined as an approach to develop novel natural compounds that can modulate NOP receptor activity. The selected phytochemicals are well-known for their antioxidant abilities and are derived either from natural alkaloids (betanin), polyphenols (gallic acid and sinapic acid) or terpenes (pomolic acid). Each of the phytochemicals selected are antioxidants which may play a role in mitigating diseases. Three conjugates of betanin were designed with each peptide by conjugating each of the three carboxylic acid groups of betanin with the peptides, while all others were mono-conjugates. Our results indicated that the betanin conjugates with both peptides showed strong binding interactions while the pomolate-peptide conjugates showed moderate binding. In general, NPFF and its conjugates showed stronger binding with the receptor. Docking and molecular dynamics studies revealed that binding interactions occurred at the binding pocket encompassing the transmembrane helices TM1, TM3 and TM7 in most cases, with the ligands binding deep within the hydrophobic core. The binding interactions were further confirmed experimentally through SPR analysis, which also showed higher binding with the betanin conjugates. MMGBSA studies indicated that the binding energies of MiF-1 conjugates were higher compared to neat MiF-1. However, in the case of NPFF, while the betanin conjugates showed enhancement, in some cases the binding energies were found to be slightly reduced compared to neat NPFF. Overall our studies reveal that such natural phytochemical derivatives that can bind to the NOP receptor when conjugated to the mammalian amidated neuropeptide NPFF and the short sequence of melanocyte inhibiting factor MiF-1 may be potentially developed for further laboratory studies for potential pharmaceutical applications.

中文翻译：

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探索 NOP 受体与设计的天然植物化学神经肽缀合物的结合相互作用：计算机模拟和 SPR 研究

伤害感受肽/孤啡肽 FQ 肽 (NOP) 受体被认为是 G 蛋白偶联受体 (GPCR) 的阿片受体亚家族的成员，该受体已被证明存在于中枢神经系统 (CNS) 的许多部位。它在疼痛调节、免疫反应和神经退行性疾病中发挥着生物学上不同的作用。在这项工作中，开发了两种已知神经肽、黑素细胞抑制因子 (MiF-1) 和具有疼痛调节能力的哺乳动物酰胺化神经肽 NPFF 的植物化学缀合物。研究了这些缀合物与 NOP 受体的结合相互作用，作为开发可调节 NOP 受体活性的新型天然化合物的方法。所选植物化学物质以其抗氧化能力而闻名，源自天然生物碱（甜菜碱）、多酚（没食子酸和芥子酸）或萜烯（苹果酸）。所选择的每种植物化学物质都是抗氧化剂，可以在减轻疾病方面发挥作用。通过将甜菜苷的三个羧酸基团中的每一个与肽缀合，设计了每种肽的三种甜菜苷缀合物，而所有其他缀合物都是单缀合物。我们的结果表明，甜菜苷与两种肽的缀合物显示出强烈的结合相互作用，而泊莫酸-肽缀合物则显示出中等的结合。一般来说，NPFF 及其缀合物与受体的结合力更强。对接和分子动力学研究表明，在大多数情况下，结合相互作用发生在包含跨膜螺旋 TM1、TM3 和 TM7 的结合袋处，配体在疏水核心深处结合。通过 SPR 分析进一步证实了结合相互作用，这也表明与甜菜苷缀合物具有更高的结合力。MMGBSA 研究表明，MiF-1 缀合物的结合能比纯 MiF-1 更高。然而，在 NPFF 的情况下，虽然甜菜苷缀合物显示出增强，但在某些情况下，发现与纯 NPFF 相比，结合能略有降低。总体而言，我们的研究表明，当与哺乳动物酰胺化神经肽 NPFF 和黑素细胞抑制因子 MiF-1 短序列缀合时，可以与 NOP 受体结合的天然植物化学衍生物可能会被开发用于进一步的实验室研究，以实现潜在的药物应用。