Tetanus toxin (TeNT) is a tetanus toxin, a highly toxic toxin produced by Clostridium tetani. Tetanus neurotoxin is part of the Clostridium neurotoxin (CNT) family, which also includes seven confirmed and two possible new BoNT serotypes, sharing approximately 35% sequence identity. TeNT primarily attacks the central nervous system, triggering persistent rigidity and paroxysmal spasms of skeletal muscles throughout the body by blocking the release of inhibitory neurotransmitters. Despite its extremely high pathogenicity, TeNT's highly specific neuronal targeting ability and irreversible synaptic silencing properties make it a promising candidate for targeted therapy and novel drug development.
Structure of TeNT
TeNT consists of 1315 amino acids with a molecular weight of approximately 150 kDa. Tetanus toxin is composed of two chains: a light chain (segment A) and a heavy chain. TeNT is cleaved post-translational by bacterial or host proteases into an active double-stranded form linked by a single disulfide bond. The heavy chain contains two functional domains: segment C is responsible for binding to nerve cells, while segment B mediates the passage of segment A across the vesicle membrane into the cytoplasm. Segment C consists of two subdomains: HCC and HCN. HCC is involved in the binding of the toxin to neurons. The light chain (LC) consists of an N-terminal catalytic domain, a 50 kDa zinc protease that specifically cleaves SNARE protein members. These proteins form a complex that promotes cellular secretion by fusing vesicles to the plasma membrane. Cleavage of presynaptic SNAREs prevents the formation of this complex and leads to inhibition of neurotransmission.
(Data source: Masuyer G, et al. EMBO Rep. 2017)
Mechanism of TeNT nerve palsy
The different transport pathways of TeNT and BoNT within neurons are not mutually exclusive, because TeNT can cause localized flaccid paralysis, while BoNTs can migrate retrogradely within neurons and be released at various levels of the central nervous system, and the effect of BoNT leads to paralysis of peripheral motor neurons.
TeNTs and BoNTs function through similar mechanisms at their specific presynaptic nerve terminal targets, strictly related to their modular structure, which comprises five main steps: presynaptic membrane binding, endocytosis within synaptic vesicles, translocation of the L domain to the cytoplasmic membrane assisted by the HN domain, reduction of trans-chain disulfide bonds by activating the L metalloproteinase domain, and selective cleavage of one or more of the three SNARE proteins, thereby blocking neurotransmitter release.
(Data source: Pirazzini M, et al. Arch Toxicol. 2022)
Targeted therapy for TeNT
Siltartoxatug (TNM002) is a monoclonal antibody targeting TeNT, developed by Trinomab. It neutralizes the toxic effects on the target human nervous system by binding to tetanus toxin. Siltartoxatug injection is used for emergency tetanus prevention in adults. In March 2022, Siltartoxatug injection received Breakthrough Therapy Designation from the China Center for Drug Evaluation (CDE). This is the first innovative anti-infective biologic in China to receive this honor. Siltartoxatug injection is expected to receive marketing approval in China in February 2025. Siltartoxatug injection is manufactured using recombinant biotechnology, thus effectively overcoming safety concerns associated with blood-derived products while providing high specificity, efficacy, and broad availability. These superior characteristics make Siltartoxatug injection a next-generation innovative solution for tetanus infection prevention.
(Data source: Trinomab official website)
Vecantoxatug (GR 2001) is a monoclonal antibody targeting tetanus toxin developed by Genrix Biopharmaceutical for passive tetanus immunization.
On May 4, 2021, a research team led by Liao Huaxin from Jinan University, in collaboration with Tsinghua University and Trinomab Biotech, published a study in Cell Reports. TechNubio discovered four naturally occurring fully human monoclonal antibodies against tetanus toxin (TeNT) with highly efficient neutralizing capabilities, any single antibody capable of effectively neutralizing tetanus toxin . They investigated the structural basis of their binding, finding that TT0067 binds to fragment C of TeNT and prevents TeNT from binding to gangliosides. The co-crystal structure of TT0067 and TeNT fragment C at 2.0 Å resolution showed that mAb TT0067 directly occupies the W pocket of one of the receptor binding sites of TeNT, thereby preventing TeNT from binding to gangliosides on the surface of host cells. This study reveals the mechanism of action of anti-TeNT neutralizing antibodies at the atomic level. The study also identified key neutralizing epitopes on TeNT fragment C, providing crucial information for developing TeNT fragment C into better and safer tetanus vaccines.
(Data source: Wang Y, et al. Cell Rep. 2021)
