Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone involved in regulating glucose and lipid metabolism. GIP receptor (GIPR) antagonism is believed to offer therapeutic potential for various metabolic diseases. Pharmacological intervention of GIPR, however, has limited success due to lack of effective antagonistic reagents. Previously we reported the discovery of two mouse anti-murine GIPR monoclonal antibodies (mAbs) with distinctive properties in rodent models. Here, we report the detailed structural and biochemical characterization of these two antibodies, mAb1 and mAb2. In vitro and in vivo characterizations demonstrated mAb2 is a full GIPR antagonistic antibody and mAb1 is a non-neutralizing GIPR binder. To understand the molecular basis of these two antibodies, we determined the co-crystal structures of GIPR extracellular domain in complex with mAb1 and with mAb2 at resolutions of 2.1 and 2.6 Å, respectively. While the non-neutralizing mAb1 binds to GIPR without competing with the ligand peptide, mAb2 not only partially occludes the ligand peptide binding, but also recognizes the GIPR C-terminal stalk region in a helical conformation that acts as a molecular mimic of the ligand peptide and locks GIPR in a novel auto-inhibited state. Furthermore, administration of mAb2 in diet-induced obesity mice for 7 weeks leads to both reduction in body weight gain and improvement of metabolic profiles. In contrast, mAb1 has no effect on body weight or other metabolic improvement. Together, our studies reveal the unique molecular mechanism of action underlying the superior antagonistic activity of mAb2 and signify the promising therapeutic potential of effective GIPR antagonism for the treatment of metabolic disorders.

中文翻译：

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抗葡萄糖依赖性促胰岛素多肽受体的拮抗抗体的分子机理。

葡萄糖依赖性促胰岛素多肽（GIP）是一种肠降血糖素激素，参与调节葡萄糖和脂质代谢。GIP受体（GIPR）拮抗作用被认为可为各种代谢性疾病提供治疗潜力。但是，由于缺乏有效的拮抗剂，GIPR的药理干预作用有限。先前，我们报道了在啮齿动物模型中发现两种具有独特特性的小鼠抗鼠GIPR单克隆抗体（mAb）的发现。在这里，我们报告这两种抗体mAb1和mAb2的详细结构和生化特征。体外和体内表征证明mAb2是完整的GIPR拮抗抗体，mAb1是非中和的GIPR结合物。要了解这两种抗体的分子基础，我们确定了GIPR细胞外域与mAb1和mAb2的复合物的共晶体结构，其分辨率分别为2.1和2.6Å。非中和性mAb1与GIPR结合而不与配体肽竞争时，mAb2不仅部分地阻断了配体肽结合，而且还识别了螺旋构象中的GIPR C末端茎区域，这是配体肽的分子模拟并将GIPR锁定为一种新颖的自动禁止状态。此外，在饮食诱导的肥胖小鼠中施用mAb2 7周可导致体重增加减少和代谢状况改善。相反，mAb1对体重或其他代谢改善没有影响。一起，