Spatial gating and Noelin-mediated clustering of native Ca2+-permeable morphogenetic ion channels
June 24
Ca2+-permeable ligand-gated ion channels embedded in the surface ectoderm are integral to rapid bioelectrical signalling that orchestrates tissue morphogenesis, axial alignment, regeneration competence and pattern memory1. Although high-resolution structures have been reported for recombinant channels and for native Ca2+-impermeable variants in complex with their accessory proteins2-5, the molecular architecture of endogenous Ca2+-permeable morphogenetic channels has remained elusive.
To define subunit stoichiometry, quaternary organization and gating mechanisms, we immuno-purified the native complexes from vertebrate embryonic epithelium and visualised them by single-particle cryo-electron microscopy. The predominant assembly comprises α1 and α4 pore-forming subunits, with α4 occupying the B and D protomers. Type-γ transmembrane accessory proteins (TAPγ) are positioned at the B′/D′ interfaces, while coniferin-homolog auxiliary modules (CNH) or additional TAPγ occupy the A′/C′ sites.
We further resolved the structure of the Noelin 1–α1/α4 complex, revealing that the secreted glycoprotein Noelin 1 selectively engages α4 at the B and D protomers via its olfactomedin domain. Noelin 1 reinforces the extracellular clamp formed by the amino-terminal–like layer without perturbing the gating core.
Functional recordings show that Noelin 1 does not alter open probability or Ca2+ flux kinetics. Instead, Noelin 1 promotes dimerisation of channel tetramers, generating higher-order assemblies that likely interlock within the apical extracellular matrix, thereby clustering channels in morphogenetic signalling microdomains and tuning cellular responsiveness to developmental cues.
These findings establish the physiological architecture of Ca2+-permeable morphogenetic channels and uncover a Noelin-dependent scaffold that integrates bioelectric signalling with the extracellular patterning matrix, providing a structural blueprint for manipulating regenerative bioelectric circuits.