TANC1

TANC1 is a multidomain scaffold protein that organizes excitatory postsynaptic signaling and also controls myoblast fusion as a developmental switch (PMID:21068316, PMID:22182840). At the synapse, TANC1 binds PSD-95 through its C-terminal PDZ-binding motif, and its overexpression drives dendritic spine formation and increases excitatory synapse number in a manner that depends on this motif; loss of TANC1 in mice reduces CA3 hippocampal spine density and impairs spatial memory (PMID:21068316). The same PDZ-binding motif recruits additional PDZ-domain proteins, extending TANC1's role as a postsynaptic organizer (PMID:34014514). TANC1 is a target of Rap2 signaling: it is bound and phosphorylated by the Rap2 effector kinases MINK and TNIK, the MINK interaction being GTP-dependent (PMID:18930710). Through its TPR domain TANC1 engages the coiled-coil/C-extension region of Myo18a via charge-based contacts, and this complex drives liquid-liquid phase separation in vitro and in cells, providing a mechanism for condensing scaffold assemblies (PMID:38092135). Structurally, TANC1 is a STAND/NACHT ATPase that rests in a closed, autoinhibited conformation stabilized by a '226-231 lock' segment, contrasting with its paralog Tanc2, whose disease mutations cause ATPase hyperactivation (PMID:42035792). Independently of its neuronal role, TANC1 is upregulated by PAX-FOXO1 to block differentiation while being essential for myoblast fusion; reducing TANC1 in rhabdomyosarcoma cells reverses the neoplastic state and restores syncytial muscle formation (PMID:22182840). Disease-associated missense variants in the ankyrin-repeat domain have been characterized biochemically, with cancer-associated mutations strongly destabilizing the domain (PMID:31040020).

1. 2008 Medium

   Established that TANC1 is a downstream node of Rap2 signaling by identifying it as a substrate of the GTP-regulated effector kinases MINK and TNIK, placing TANC1 within a defined small-GTPase signaling cascade.

   Evidence Affinity chromatography/MS, yeast two-hybrid, co-IP, and phosphorylation assays in cultured cells

   PMID:18930710

   Open questions at the time

   • Functional consequence of TANC1 phosphorylation not defined
   • Phosphosites not mapped
   • Single-lab characterization
2. 2010 High

   Defined TANC1 as a postsynaptic scaffold that promotes dendritic spine and excitatory synapse formation through its PDZ-binding motif binding PSD-95, with knockout mice linking this to hippocampal spine density and spatial memory.

   Evidence Neuronal overexpression/dominant-negative experiments, TANC1 knockout mouse spine morphometry and behavior, PDZ-motif domain mapping

   PMID:21068316

   Open questions at the time

   • Whether PSD-95 binding fully accounts for the spine phenotype not resolved
   • Region specificity (CA3) mechanism unexplained
   • Molecular mechanism of spine maintenance not detailed
3. 2011 High

   Revealed a non-neuronal role for TANC1 as a PAX-FOXO1-induced differentiation block essential for myoblast fusion, with direct relevance to rhabdomyosarcoma where its reduction restores muscle differentiation.

   Evidence Mammalian myoblast RNAi, Drosophila rols genetic epistasis, PAX-FOXO1 overexpression with TANC1 RNAi rescue

   PMID:22182840

   Open questions at the time

   • Molecular fusion machinery engaged by TANC1 not identified
   • How a synaptic scaffold operates in fusion mechanistically unclear
   • Direct PAX-FOXO1 transcriptional regulation of TANC1 not dissected
4. 2019 Medium

   Provided biochemical characterization of the ankyrin-repeat domain and showed that disease variants differ in impact, with cancer-associated mutations destabilizing the fold while intellectual-disability variants had marginal effects.

   Evidence Recombinant protein purification, SEC-MALS, circular dichroism, site-directed mutagenesis

   PMID:31040020

   Open questions at the time

   • Functional/binding consequences of destabilization not tested in cells
   • Engineered capping units differ from native protein
   • Partners mediated by the AR domain not identified
5. 2021 Low

   Extended the TANC1 interactome by identifying multiple PDZ-domain proteins captured through its C-terminal PDZ-binding motif, broadening its scaffolding repertoire beyond PSD-95.

   Evidence Immunopurification and peptide-based affinity purification with mass spectrometry

   PMID:34014514

   Open questions at the time

   • Single AP-MS approach without orthogonal validation of individual partners
   • Functional relevance of new partners untested
   • Cellular context of interactions undefined
6. 2023 Medium

   Identified a direct TPR-domain interaction with Myo18a and demonstrated that the complex undergoes liquid-liquid phase separation, providing a biophysical mechanism for TANC1-driven condensate assembly.

   Evidence Size exclusion chromatography, high-salt disruption, LLPS assays in vitro and in cultured cells

   PMID:38092135

   Open questions at the time

   • Physiological role of TANC1-Myo18a condensates not established in neurons
   • Regulation of LLPS not defined
   • Single-lab characterization
7. 2026 High

   Resolved TANC1 as a STAND/NACHT ATPase held in an autoinhibited closed state by a '226-231 lock', defining a structural/enzymatic basis for the protein and contrasting it with hyperactivating disease mutations in its paralog Tanc2.

   Evidence Cryo-EM structure determination, ATPase assays, cellular oligomerization/puncta assays, disease-mutation mutagenesis

   PMID:42035792

   Open questions at the time

   • Conditions that release TANC1 autoinhibition not identified
   • Whether TANC1 (vs Tanc2) oligomerizes/has ATPase activity in vivo unclear
   • Link between ATPase state and synaptic scaffolding function unestablished

• How TANC1's STAND/NACHT ATPase conformational switching is coupled to its scaffolding functions at synapses and in myoblast fusion, and what signals release its autoinhibited state, remain unknown.
• No physiological activator of TANC1 ATPase identified
• Integration of Rap2/MINK phosphorylation with conformational state untested
• Mechanistic unity of synaptic vs myogenic roles unresolved