TOM40

TgTom40 is a core component of the translocon of the outer mitochondrial membrane (TOM) complex in Toxoplasma gondii, where it is required for mitochondrial protein import and parasite survival (PMID:27458014). Beyond its canonical import function, TgTom40 additionally serves as a molecular tether at nuclear-mitochondrial membrane contact sites: it interacts with nuclear pore components including TgNup503, and its genetic disruption reduces the abundance of these contact sites, establishing a role in mediating mitochondrial-nuclear membrane apposition (PMID:38456969). No further mechanistic detail—including structural organization of the channel or a defined substrate repertoire—has been characterized in the available corpus.

1. 2016 Medium

   Establishing that apicomplexan mitochondria possess a conserved import machinery, this work identified TgTom40 as a component of the TOM complex required for mitochondrial protein import and parasite survival, defining the core import route in T. gondii.

   Evidence Homologue identification and functional characterization of TOM complex components, using TgTom22 and TgTom7 as experimental handles for complex assembly and import assays

   PMID:27458014

   Open questions at the time

   • TgTom40's role is inferred from complex membership rather than its own loss-of-function experiment
   • No structural model of the TgTom40 channel
   • Substrate repertoire imported through the complex not defined
2. 2024 Medium

   Testing whether a mitochondrial import component has functions beyond translocation, this work showed TgTom40 acts as a molecular tether at nuclear-mitochondrial contact sites by interacting with nuclear pore components, revealing an inter-organelle scaffolding role.

   Evidence Conditional genetic depletion of TgTom40 with quantitative imaging of membrane contact sites, plus identification of co-interaction between nuclear pore (TgNup503) and TOM translocon components

   PMID:38456969

   Open questions at the time

   • Full reciprocal Co-IP and structural validation of the tether interaction not described
   • Whether the tethering function is separable from the import function is unresolved
   • Functional consequence of contact-site loss for parasite physiology not established

• Whether TgTom40's import channel activity and its membrane-tethering role are mechanistically coupled, and how substrate selection and translocation occur at the molecular level, remain open.
• No direct loss-of-function characterization of TgTom40 in the import context
• No structural determination of the TOM channel in T. gondii
• Mechanism coupling import and tethering functions unknown