"The puffer fish (also known as the pufferfish) is the favorite of the gluttons, but they are terrified because of their deathly toxicity, and even so, they still can't stop foodies from coming forward for thousands of years. Before the chemical composition of the pufferfish toxin was known, the toxicity of the pufferfish has been widely recorded, and its traces can be found in the "Classic of Mountains and Seas", "Shennong Materia Medica", "Compendium of Materia Medica", etc., and there are also historical records in Egypt, Japan, Mexico and other countries. The toxicity of pufferfish toxin is much higher than that of arsenic, potassium cyanide, etc., if it enters the bloodstream, it can be killed by reaching a trace amount of 8 micrograms per kilogram in mice, which is one of the most toxic neurotoxins in nature.
In the mid-twentieth century, with the study of the action potential of the nervous system, scientists found that the toxicity of the pufferfish toxin (TTX) was due to the highly specific blocking of sodium ion channels and thus inhibiting the production of action potentials, resulting in nerve and muscle paralysis.
(Pufferfish.) Image source: https://curiosity.com/topics/pufferfish-are-incredibly-poisonous-so-why-do-people-eat-them-curiosity/)
In addition to pufferfish toxin, there is a class of small molecule neurotoxins with similar structures collectively known as shellfish toxin (SAXItoxin, abbreviated as STX), which is the most toxic marine biological toxin, of which the binding ability of stone clam toxin and sodium ion channels is even higher than that of pufferfish toxin, which is the main cause of nerve paralysis poisoning caused by accidental ingestion of toxic shellfish.
Because TTX and STX have ultra-high specific inhibition of sodium ion channels, they have been used as molecular probes to identify sodium channels since the 1970s. So far, the 9 human sodium channel subtypes are divided into TTX-sensitive and non-sensitive types according to their binding ability to TTX.
In addition to the small molecule blockers of TTX and STX, there are a variety of peptide toxins in nature, such as snakes, scorpions, centipedes, spiders, and toads (please refer to the Five Poisons of "Laughing At the Lake") The venom contains thousands of peptide toxins of different lengths and compositions. Animals use these toxins for self-defense or hunting. A considerable part of the peptide acts directly on the voltage-gated sodium ion channel, causing paralysis of prey or severe pain in the bitten person. These peptide toxins generally do not directly hinder ion permeability, but cause abnormal activation (opening) or inactivation (shutdown) of sodium ion channels by acting on the voltage receptor domain of these channels, so these toxins are called "gating modifier toxin" (GMT). Due to the diversity and specific selectivity of these toxins, they are more suitable for the right medicine, and it is expected to develop specific analgesics or insecticides with small side effects based on understanding their interaction with specific subtypes of sodium ion channels, so the structure of these toxins and sodium ion channel complexes has been of concern to academics, pharmaceuticals, and agriculture. However, due to the difficulty of structural analysis of the sodium channel itself, such structural information is completely blank.
On July 26, 2018, Beijing time, Yan Ning's research group published a long research article entitled "Structural basis for the modulation of voltage-gated sodium channels by animal toxins" in the journal Science online. The voltage-gated sodium ion channel NavPaS and the gated regulating toxin Dc1a were analyzed, and the cryo-EM structure of pufferfish toxin (TTX) and shellfish toxin (STX) was added on this basis, and the overall resolution reached 2.8, 2.6 and 3.2, respectively, and the mechanism of action of the voltage-gated sodium ion channel and related toxins was elaborated.
The study analyzed the cryo-EM structures of voltage-gated sodium ion channel NavPaS and gated regulators Dc1a, NavPaS and Dc1a plus pufferfish toxin (TTX) and NavPaS and Dc1a plus stone house clam toxin (STX), respectively, with overall resolutions of 2.8, 2.6 and 3.2, respectively. On this basis, the researchers carefully analyzed the structure and elaborated on the mechanism of action of voltage-gated sodium ion channels with TTX and STX and its regulation by the gated regulator Dc1a. In addition, the researchers also saw a sodium ion bound in the selectivity filter in the structure, combined with previous molecular dynamics simulation studies, the article proposed a possible mechanism for the selectivity of sodium ions in such channels.
It is worth mentioning that 2.6 is currently the highest resolution known to use cryo-EM technology to resolve the structure of membrane proteins, and the bound TTX, STX small molecules and sodium ions can be clearly seen. Such a high resolution was only obtained through a 2-day period of data collected at Tsinghua University's powerful electron microscopy platform. This structural analysis once again shows the great potential of cryo-EM technology in drug screening in the future.
This work is another important breakthrough in the study of ion channels after yanning research group successfully analyzed the structure of the first eukaryotic calcium ion channel, the first eukaryotic sodium ion channel structure, and the structure of the first sodium ion channel and the regulated subunit complex at Tsinghua University, laying the foundation for the transformation and application from basic research to transformation application.
Professor Yan Ning, former professor of the School of Life Sciences and Center for Advanced Innovation in Structural Biology of Tsinghua University, is the corresponding author of the research paper, and Zhou Qiang, an associate researcher at the School of Medicine, and Professor Glenn F. King of the University of Queensland, Australia, who provided Dc1a and conducted related functional analysis, are co-corresponding authors. Shen Huaizong, postdoctoral fellow of Tsinghua University School of Medicine and outstanding scholar of Structural Biology High-precision Innovation Center, Li Zhangqiang, CLS doctoral student, Jiang Yan, doctoral student of the University of Queensland, and Pan Xiaojing, postdoctoral fellow of The School of Medicine and outstanding scholar of Structural Biology High-precision Innovation Center, are co-first authors. Dr. Wu Jianping, a former doctoral student at tsinghua University's School of Life Sciences, also participated in the study. The corresponding author and first author affiliations are both Tsinghua University. The National Protein Science Center (Beijing) Tsinghua University Cryo-EM Platform and Tsinghua University High Performance Computing Platform respectively supported the data collection and data processing of the study, especially Dr. Lei Jianlin of the Cryo-EM Platform of Tsinghua University for guiding the data collection and thanking the other staff of the platform. Beijing Advanced Innovation Center for Structural Biology (Tsinghua), Joint Center for Life Sciences (Tsinghua University), State Key Laboratory of Biofilm and Membrane Bioengineering, Ministry of Science and Technology and Foundation Committee provided financial support for the research. After joining Princeton University, Professor Yan ning was supported by a special grant from the Shirley Tilghman Chair Professor.
Original link:
http://science.sciencemag.org/content/early/2018/07/25/science.aau2596
Links to related articles:
NavRh:
http://www.nature.com/nature/journal/v486/n7401/full/nature11054.html
Cav1.1：
http://science.sciencemag.org/content/350/6267/aad2395.long
http://www.nature.com/nature/journal/v537/n7619/full/nature19321.html
NavPaS：
http://science.sciencemag.org/content/355/6328/eaal4326
Electric Eel Nav1.4- β1 complex：
https://www.sciencedirect.com/science/article/pii/S0092867417307584