In this amazing video from National Geographic, a mongoose is shown winning a battle with an Asian cobra. How can these cute animals compete against such a deadly snake?
It turns out that the mongoose is resistant to snake venom, specifically, alpha-bungarotoxin. This toxin is lethal to many creatures because of its ability to block nicotinic acetylcholine receptors (nAChR). These receptors were aptly named after their affinity for the drug nicotine and are found on the surface of muscle cells where nerves containing acetylcholine are also located. Here, they are able to respond to acetylcholine released from nerves to regulate muscle contraction. You can imagine that if alpha-bungarotoxin blocks these receptors, it would have a serious impact on the ability of muscles to contract. This is how the toxin causes respiratory failure (you need muscles to breathe), paralysis and eventually death.
So how does the mongoose resist the lethal venom? Researchers have found that the mongoose nAChR is structurally resistant to the binding of alpha-bungarotoxin and binds acetylcholine with a much higher affinity than the toxin.
Asher et al., Functional characterization of mongoose nicotinic acetylcholine receptor alpha-subunit: resistance to alpha-bungarotoxin and high sensitivity to acetylcholine. FEBS Letters. 431(3):411-4, 1998.