Ta3a (Delta-myrmicitoxin-Ta3a) is a vertebrate-selective neurotoxin found in the venom of the African ant species Tetramorium africanum. It is known to cause intense, long-lasting pain by targeting voltage-gated sodium channels in peripheral sensory neurons. Ta3a increases the duration of active single-channel periods and reduces sodium channel inactivation, leading to heightened neuronal excitability.
| Delta-myrmicitoxin-Ta3a | |||||||
|---|---|---|---|---|---|---|---|
 Ta3a structure prediction from AlphaFold | |||||||
| Identifiers | |||||||
| Organism | |||||||
| Symbol | ? | ||||||
| UniProt | P0DX61 | ||||||
| |||||||
| Identifiers | |
|---|---|
3D model (JSmol)
|
|
| |
| |
| Properties | |
| C159H248N36O38 | |
| Molar mass | 3271.947 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Chemistry
editTa3a belongs to the aculeatoxin family of peptides, found in the venom of Hymenoptera.[1] It is a 29-residue peptide, which is predicted to have an alpha-helical structure (amino acid sequence: LAPIFALLLLSGLFSLPALQHYIEKNYIN).[1] [2] Ta3a is similar to poneratoxin, a voltage-gated sodium channel toxin found in the ant species Paraponera clavata, as well as to other uncharacterised peptides from various other ant species.[1]
Target
editTa3a targets voltage-gated sodium channels such as Nav1.6, Nav1.7 and Nav1.8, which are involved in peripheral pain signaling.[1][3] The half-maximal effective concentration (EC50) of Ta3a for the human Nav1.7 channel is 30 ± 9 nM.[1] Nav1.6 is similarly sensitive to Ta3a with an EC50 of 25 ± 2 nM, while Nav1.8 is less sensitive with an EC50 of 331 ± 58 nM.[1]
Mode of action
editTa3a exerts a significant regulatory effect on voltage-gated sodium channels, particularly through its interaction with the Nav1.7 subtype. It prolongs the duration that the channel remains active and increases the likelihood of the channel being open. Additionally, Ta3a shifts the activation of Nav1.7 to more negative (hyperpolarized) potentials, allowing Nav1.7 channels to remain active for extended periods even in the absence of additional voltage stimuli. These prolonged, non-inactivating currents cause significant changes in the cell's membrane potential, due to the continuous sodium influx. Such prolonged sodium channel activation also permits sodium currents to persist at very low membrane potentials. The mechanism of action of Ta3a is believed to involve the stabilization of the S4 voltage-sensing domain of Nav1.7 channels in their "activated" conformation, thereby maintaining channel activity. The S4 region contains multiple positively charged amino acid residues that respond to changes in membrane potential.[4] Thus, Ta3a likely interacts with the S4 region, leading to channel activation at lower voltages. Therefore, the amount of external voltage required for channel activation is reduced.
Toxicity
editThe hallmark of Ta3a toxicity is acute pain, which is the most immediate and prominent symptom of Ta3a exposure.[2] This is due to the excessive activation of the Nav1.7 channel, which plays a crucial role in pain transmission by enhancing the propagation of nerve signals, particularly pain-related signals. While there are no detailed studies on the effects of Ta3a on the cardiovascular or respiratory systems, overactivation of sodium channels could potentially impact cardiac cells, leading to arrhythmias or other cardiovascular complications.[5] In severe cases, prolonged sodium channel opening may also affect the central nervous system, potentially causing respiratory difficulties or paralysis.[6][7]
Treatment
editSince Ta3a primarily exerts its toxic effects by overactivating the Nav1.7 channel, sodium channel blockers represent a potential therapeutic approach. For instance, tetrodotoxin (TTX), a sodium channel blocker, has been shown to effectively inhibit the persistent currents induced by Ta3a in experimental settings.[2] However, no studies have yet been conducted on specific treatment methods for Ta3a poisoning.
References
edit- ^ a b c d e f Robinson, Samuel D.; Deuis, Jennifer R.; Touchard, Axel; Keramidas, Angelo; Mueller, Alexander; Schroeder, Christina I.; Barassé, Valentine; Walker, Andrew A.; Brinkwirth, Nina; Jami, Sina; Bonnafé, Elsa; Treilhou, Michel; Undheim, Eivind A. B.; Schmidt, Justin O.; King, Glenn F.; Vetter, Irina (23 May 2023). "Ant venoms contain vertebrate-selective pain-causing sodium channel toxins". Nature Communications. 14 (1): 2977. Bibcode:2023NatCo..14.2977R. doi:10.1038/s41467-023-38839-1. PMC 10206162. PMID 37221205.
- ^ a b c Thapa, Ashvriya; Beh, Jia Hao; Robinson, Samuel D.; Deuis, Jennifer R.; Tran, Hue; Vetter, Irina; Keramidas, Angelo (October 2024). "A venom peptide-induced NaV channel modulation mechanism involving the interplay between fixed channel charges and ionic gradients". Journal of Biological Chemistry. 300 (10): 107757. doi:10.1016/j.jbc.2024.107757. PMC 11470524. PMID 39260690.
- ^ Bennett, David L.; Clark, Alex J.; Huang, Jianying; Waxman, Stephen G.; Dib-Hajj, Sulayman D. (1 April 2019). "The Role of Voltage-Gated Sodium Channels in Pain Signaling". Physiological Reviews. 99 (2): 1079–1151. doi:10.1152/physrev.00052.2017. PMID 30672368.
- ^ Dib-Hajj, Sulayman D.; Yang, Yang; Black, Joel A.; Waxman, Stephen G. (January 2013). "The NaV1.7 sodium channel: from molecule to man". Nature Reviews Neuroscience. 14 (1): 49–62. doi:10.1038/nrn3404. PMID 23232607.
- ^ Bennett, Paul B.; Yazawa, Kazuto; Makita, Naomasa; George, Alfred L. (August 1995). "Molecular mechanism for an inherited cardiac arrhythmia". Nature. 376 (6542): 683–685. Bibcode:1995Natur.376..683B. doi:10.1038/376683a0. PMID 7651517.
- ^ Cummins, Theodore R; Rush, Anthony M (November 2007). "Voltage-gated sodium channel blockers for the treatment of neuropathic pain". Expert Review of Neurotherapeutics. 7 (11): 1597–1612. doi:10.1586/14737175.7.11.1597. PMID 17997706.
- ^ Cannon, Stephen C. (March 1996). "Sodium Channel Defects in Myotonia and Periodic Paralysis". Annual Review of Neuroscience. 19 (1): 141–164. doi:10.1146/annurev.ne.19.030196.001041. PMID 8833439.