Even on a continent notorious for venomous creatures, brown snakes stand out. Not only are eastern brown snakes considered the second most venomous land snake in the world, but their aggression and habitat close to major population centers mean they account for more than half of Australia's snake bite deaths.
Although antivenoms have existed against brown snakes for decades, we haven't known that much about the molecules involved, something Dr Bryan Fry and colleagues at the University of Queensland set out to address. In Comparative Biochemistry and Physiology, they report two major new discoveries lurking in the venom of the eastern brown snake and seven of the other eight members of the Pseudonaja genus.
One discovery explains why brown snakes are so dangerous. “It was previously known that brown snakes are like taipans in converting a protein called prothrombin into thrombin, which in turn forms the blood clot,” Fry said in a statement. “However, the speed of action could not be accounted for based on this action alone. Our team discovered brown snakes are potent in activating Factor VII, another blood clotting enzyme.”
Interactions between Factor VII and thrombin create what Fry called a “venomous vortex” leading to exceptionally rapid action, decreasing the chances their prey will escape, or a human will make it to a hospital in time.
Venoms are among the richest parts of nature's medicine chest, with captopril, possibly the most valuable drug of all time, based on Brazilian viper venom. Knowledge of molecules that cause clotting might improve hemophilia treatment, while understanding what triggers clots could prove useful in stroke prevention.
Of less obvious use, but possibly more interest, is the discovery that baby brown snakes have completely different venom from adults. “This is because young brown snakes specialize in lizards, then specialize in mammals as adults,” Fry said. The juvenile venom makes lizards go limp, while the adult version causes strokes in rodents and small marsupials.
Fry told IFLScience other snakes shift the concentration of molecules as they age, but nothing this dramatic has previously been recorded. Having only compared the young snakes when they are “the size of a child's shoelace” with the adults, Fry doesn't know at what point the venoms change, or whether adolescent brown snakes have a period of overlap, or an angry teenage phase where nothing seems to work.
Fry thinks it “would be logical” if the venom changes at the same time as the young snakes lose their banded coloring and shift to a more even shades, but he can't be sure. He stresses that even though the baby brown snake venom is mainly suited to killing other reptiles it still has potent neurotoxins for mammals, so they shouldn't be messed with.