Cryo-EM structure of the full-length LGR4-RSPOs complex and a targeting nanobody for anti-obesity therapy

Obesity poses a substantial threat to human health but lacks effective management. Recent advancements in large-scale deep sequencing and cryo-electron microscopy (cryo-EM) have transformed drug discovery paradigms. Leveraging prior genetics investigation, we pinpointed Leucine-rich repeat-containing G protein–coupled receptor 4 (LGR4) as a promising target for combating obesity. Here, we present cryo-EM structures of full-length LGR4 alone and in complex with RSPO2(FU). Notably, we develop an inhibitory nanobody (NB21) that blocks the binding of RSPO1/2 to LGR4, and we also determine the structure of the LGR4-NB21 complex. NB21-mFc (NB21 fused with mouse IgG2) effectively inhibits the canonical Wnt signaling pathway, thereby enhancing mitochondrial respiration and thermogenesis in beige adipocytes. In vivo, NB21-mFc increases energy expenditure by promoting the browning of white fat, conferring resistance to both diet-induced and genetic (ob/ob) obesity. Furthermore, LGR4 deficiency abolishes the effects of NB21-mFc in boosting the browning program and subsequent weight reduction. In summary, our study unveils structural insights into the LGR4-RSPOs and LGR4-NB21 complexes, paving the way for the development of an LGR4–targeting nanobody for weight loss. The study reveals a nanobody that blocks LGR4 to activate fat browning and combat obesity, offering structural insights and a potential strategy for weight loss therapy.