Tetramethylenedisulfotetramine (TETS) is a so-called “caged” convulsant that is responsible for thousands of accidental and malicious poisonings. Similar to the widely used GABA receptor type A (GABA A ) antagonist picrotoxinin, TETS has been proposed to bind to the noncompetitive antagonist (NCA) site in the pore of the receptor channel. However, the TETS binding site has never been experimentally mapped, and we here set out to gain atomistic level insights into how TETS inhibits the human α 2 β 3 γ 2 GABA A receptor. Using the Rosetta molecular modeling suite, we generated three homology models of the α 2 β 3 γ 2 receptor in the open, desensitized, and closed/resting state. Three different ligand-docking algorithms (RosettaLigand, Glide, and Swissdock) identified two possible TETS binding sites in the channel pore. Using a combination of site-directed mutagenesis, electrophysiology, and modeling to probe both sites, we demonstrate that TETS binds at the T6′ ring in the closed/resting-state model, in which it shows perfect space complementarity and forms hydrogen bonds or makes hydrophobic interactions with all five pore-lining threonine residues of the pentameric receptor. Mutating T6′ in either the α 2 or β 3 subunit reduces the IC 50 of TETS by ∼700-fold in whole-cell patch-clamp experiments. TETS is thus interacting at the NCA site in the pore of the GABA A receptor at a location that is overlapping but not identical to the picrotoxinin binding site. SIGNIFICANCE STATEMENT Our study identifies the binding site of the highly toxic convulsant tetramethylenedisulfotetramine (TETS), which is classified as a threat agent by the World Health Organization. Using a combination of homology protein modeling, ligand docking, site-directed mutagenesis, and electrophysiology, we show that TETS is binding in the pore of the α 2 β 3 γ 2 GABA receptor type A receptor at the so-called T6′ ring, wherein five threonine residues line the permeation pathway of the pentameric receptor channel.

Objective Royal demolition explosive (RDX) can induce seizures in wildlife and humans following release into the environment or after voluntary consumption. During the Vietnam War, RDX intoxication was the most common cause of generalized seizures in US service personnel, and in some sections of the armed forces, eating of RDX has continued as “a dare” to this day. After its mechanism of action was long unknown, RDX was recently shown to be a GABAA receptor antagonist. We here determined the GABAA receptor subtype‐selectivity of RDX and mapped its functional binding site. Methods We used whole‐cell patch‐clamp to determine the potency of RDX on 10 recombinantly expressed GABAA receptors and mapped the RDX binding site using a combination of Rosetta molecular modeling and site‐directed mutagenesis. Results RDX was found to reversibly inhibit the α1β2γ2 GABAA receptor with an IC50 of 23 μmol/L (95% CI 15.1–33.3 μmol/L), whereas α4 and α6 containing GABAA receptor combinations were 4–10‐fold less sensitive. RDX is binding to the noncompetitive antagonist (NCA) site in the pore. In a molecular model based on the cryo‐EM structure of the resting state of the α1β2γ2 receptor, RDX forms two hydrogen bonds with the threonines at the T6’ ring and makes hydrophobic interactions with the valine and alanine in 2′ position of the α1 or β2 subunits. Interpretation Our findings characterize the mechanism of action of RDX at the atomistic level and suggest that RDX‐induced seizures should be susceptible to treatment with GABAA modulating drugs such as benzodiazepines, barbiturates, propofol, or neurosteroids.

Here, we present the draft genome sequence of Pseudoalteromonas tetraodonis UCD-SED8, a marine bacterium normally associated with the production of tetrodotoxin in pufferfish. This strain was isolated from sediment samples surrounding Zostera marina roots collected from Bodega Marine, California. The assembly consists of 4,017,727 bp contained in 35 contigs.

Here, we present the draft genome sequences of Pseudoalteromonas porphyrae UCD-SED9 and UCD-SED14 (phylum Proteobacteria). These strains were isolated from sediment surrounding the roots of the seagrass, Zostera marina, collected near the UC, Davis Bodega Marine Laboratory (Bodega Bay, California). The assemblies contain 4,847,456 bp and 4,817,752 bp, respectively.

Here, we present the draft genome sequences of Vibrio splendidus UCD-SED7 and UCD-SED10 (phylum Proteobacteria). These strains were isolated from sediment surrounding Zostera marina roots near the UC Davis Bodega Marine Laboratory (Bodega, Bay, California). These assemblies contain 5,334,236 bp and 5,904,824 bp, respectively.