A green mamba bite results in dizziness, nausea, difficulty breathing, irregular heartbeats, convulsions, and sometimes death. But the snake’s deadly venom contains a small peptide that could one day save lives. Researchers led by Christiane Mendre of the University of Montpellier, Ralph Witzgall of the University of Regensburg, Nicolas Gilles of Paris-Saclay University, and colleagues plucked a peptide out of the venom that might help people with polycystic kidney disease (Proc. Natl. Acad. Sci. USA 2017, DOI: 10.1073/pnas.1620454114). These individuals develop water-filled cysts on their kidneys that interfere with the organ’s function and can eventually be fatal. Treatment for the disease currently involves so-called vaptan drugs that interfere with a protein called the type 2 vasopressin receptor. But the drugs are toxic to another organ—the liver. The team of researchers noticed that a 57-residue peptide in the green mamba venom called mambaquaretin-1 also targets the receptor but is more selective than existing drugs. “With high selectivity and without toxic metabolic by-products associated with its peptidic nature, mambaquaretin-1 could become the preferential treatment for these disorders,” they note.