Due to mutations in the ion channel Shal scolopendra can use the same venom to kill prey and fight each other. For the latter, the poison is not lethal and only causes temporary paralysis. The study of the molecular basis of this process, published in the journal Science Advance.
Many animals use venom, not only for hunting and protection from predators, but in the process of intraspecific struggle. For example, millipedes class gubonogih (Chilopoda) administered to relatives of poison as a warning signal. It is believed that these arthropods have a certain immune to their own toxins, but its mechanism is not studied.
To understand this issue decided by a team of specialists led by Siloam Yang (Yang Shilong) from the Institute of Zoology in Kunming. As a model of the object they chose the Vietnamese scolopendra Scolopendra subspinipes. With a body length of up to 20 centimeters, it is considered one of the largest centipedes, and its venom is strong enough to kill a child.
The researchers introduced in the third body segment scolopendra ten MICS of poison received from the representative of the same species. As a result, the centipede paralyzed, but after ten minutes full mobility to her back. No long-term effects on her body were recorded.
In the next stage from the body of scolopendra have identified dorsal unpaired medial neurons and tested their sensitivity to poison relatives. It turned out that the voltage-dependent calcium and sodium channels does not react to the presence of a toxin regarded as conspecific. However, other toxins, for example tetrodotoxin, affected them depressing.
The only ion channels of the centipedes that have reduced activity under the influence of the poison of their own species, appeared to be voltage-dependent potassium. However, not all of the five varieties of these proteins showed sensitivity only to the Shal channels. Testing different components of the venom, the researchers came to the conclusion that this effect is responsible neurotoxin SsTx. It inhibits Shal blocking its pores.
Shal of centipedes differ from similar proteins in other species — including those on whom these centipedes hunt. On the outside of the pore, on a plot of 351, is a negatively charged glutamate residue. When this residue was replaced by neutral or positively charged versions, the degree of affinity between the toxin and the channel was decreased. In other words, glutamate at position 351 is “anchor” that makes the Shal of centipedes, so sensitive to the SsTx. Other types of channels Shal to the poison of centipedes, insensitive.
Thus, it Shal be responsible for the effect which the poison produces on the relatives of the centipedes. But what are its functions in the body centipedes, remained unknown. To find out, the researchers created antibodies to Shal, and with their help, praised the level of expression of this protein in different tissues scolopendra.
It turned out that in the trachea and the muscles, it is not possible, however, present in the intestine and is especially abundant in the membranes of vascular cells of the heart tube and dorsal unpaired neurons. Under the influence SsTx a narrowing of blood vessels, over-stimulation of neurons and, as a result, there is temporary paralysis. When this toxin was introduced to the centipedes in a purified form, it produced the same effect as an injection of poison.
In the evolution of most ion channels of centipedes acquired mutations that made them immune to the venom of members of their own species. For example, the stability of the Shaker channel to the SsTx is provided by the presence of the arginine residue at position 399. Susceptible left only channel, Shal. Based on it formed a alarm system, that allows the centipedes to find out the relationship with neighbors, using the same poison that is used for hunting, and not to risk my life.
The specialists from the Institute of Zoology in Kunming confirmedthat the toxin SsTx is the main active component of the venom of scolopendra S. subspinipes. Especially strongly it acts on KCNQ potassium channels. To neutralize the effect of toxin may be due to drug retigabine, which is used for epilepsy.
Sergey Knee High