Mambaquaretins are a group of toxins from mamba venoms, containing seven members until now, which target the vasopressin type 2 receptor (V2R). V2R, primarily expressed in the kidney, belongs to the G-protein coupled receptor family and regulates fluid osmotic pressure and diuresis through the vasopressin hormone. The Mambaquaretin-1, the very first identified member of the Mambaquaretin group, antagonizes V2R and this property gives it potential therapeutic applications to treat disorders such as hyponatremia, syndrome of inappropriate antidiuretic hormone secretion (SIADH) or polycystic kidney diseases (PKD). PKD are severe genetic diseases which affect 1 in 1,000 people in the world. However, therapeutic strategies are very limited. An animal trial was conducted in a rodent model of PKD and demonstrated the efficacy of Mambaquaretin-1 to slow down the disease progression after a 100 days treatment, validating the toxin as a novel therapeutic strategy. The pharmacodynamics of the toxin was further investigated in healthy rats to estimate the best dose to inject regarding duration of action and side effects occurrence. To define the molecular mode of interaction between V2R and Mambaquaretin-1, a structure activity relationship study was completed. X-ray diffraction approach confirmed that the toxins adopt a Kunitz fold reticulated by three disulphide bridges. Comparing the natural SAR of the seven active Mambaquaretins and exploring the V2R activity of six toxins from databases very close in sequence, interesting positions were mutated in order to determine the pharmacophore of the Mambaquaretin-1. Consequently, we could advance a receptor-toxin complex model in which the toxin interacts both with the upper part of the orthosteric site and the extracellular loops. Thanks to these results, engineered toxins are being designed to enhance its in vivo characteristics, such as blood stability or speed of elimination in the aim to propose the best therapeutic candidate.