ERC2

ERC2/CAST1 is a presynaptic active-zone scaffolding protein that organizes the molecular cytomatrix controlling neurotransmitter release and couples it to calcium influx (PMID:22577167, PMID:16421316). It directly binds the β4- (and more weakly β1b-) subunits of voltage-dependent Ca2+ channels, and this interaction shifts the voltage dependence of channel activation toward hyperpolarization, functionally tuning Ca2+ channel gating at the active zone (PMID:22577167). Reciprocally, P/Q- and N-type VDCCs act as membrane anchors that recruit ERC2 together with Bassoon and Piccolo to the active zone; loss of these channels reduces active-zone number, docked vesicle pools, and active-zone protein levels including ERC2, establishing a mutual scaffolding relationship between the channels and the cytomatrix (PMID:21228161). ERC2 further organizes the active zone by binding the tandem-PDZ protein syntenin-1 through its C-terminal region, with multimerization of both partners driving syntenin-1 localization to presynaptic ERC2 clusters (PMID:16421316). Its self-assembly is regulated by SRPK2-mediated phosphorylation acting through the coiled-coil domains CC1 and CC4, controlling the degree of ERC2 oligomerization during active-zone assembly (PMID:31671734). A somatic ERC2 L309I mutation has been linked to Maffucci's syndrome, where it enhances angiogenesis in vitro (PMID:34790172).

1. 2006 Medium

   Established that ERC2 acts as a PDZ-organizing scaffold by identifying syntenin-1 as a direct C-terminal binding partner recruited to presynaptic ERC2 clusters, defining one route by which ERC2 builds active-zone molecular architecture.

   Evidence Yeast two-hybrid, reciprocal co-IP with domain mapping, and immunofluorescence colocalization in neurons

   PMID:16421316

   Open questions at the time

   • Functional consequence of syntenin-1 recruitment for release was not measured
   • Single-lab finding without independent replication
   • Role of multimerization in vivo not tested
2. 2011 High

   Showed that VDCCs themselves anchor ERC2 to the active zone, reframing the channel as a scaffolding hub whose loss disassembles active-zone structure and depletes ERC2.

   Evidence P/Q- and N-type VDCC double-knockout mouse with quantitative electron microscopy and confirmatory co-IP of β-subunit–ERC2 binding

   PMID:21228161

   Open questions at the time

   • Did not resolve whether ERC2 loss is direct or secondary to active-zone collapse
   • Stoichiometry of the channel–scaffold complex not defined
3. 2012 High

   Demonstrated that the ERC2–VDCC interaction is not merely structural but functional, showing ERC2 binding to the β4-subunit modulates Ca2+ channel gating.

   Evidence Co-IP from mouse brain, pull-down domain mapping, and heterologous coexpression with electrophysiology in BHK cells

   PMID:22577167

   Open questions at the time

   • Physiological impact of the gating shift on release probability not measured in neurons
   • Weak β-subunit/α1-linker interactions not fully resolved
4. 2019 Medium

   Identified a regulatory mechanism for ERC2 assembly, showing SRPK2 phosphorylates ERC2 to control its coiled-coil-dependent self-oligomerization during active-zone formation.

   Evidence Co-IP in HEK293T, SH-SY5Y and HT-22 cells, overexpression/dominant-negative manipulation, and synaptosomal fractionation

   PMID:31671734

   Open questions at the time

   • Phosphosite identity and stoichiometry not mapped
   • Effect on active-zone assembly shown in cell lines, not neurons in vivo
   • Single-lab finding
5. 2021 Low

   Linked ERC2 to a disease context outside the synapse, finding a somatic L309I mutation associated with Maffucci's syndrome that enhances angiogenesis.

   Evidence Exome sequencing of a single patient, PCR confirmation, and an in vitro angiogenesis assay with the mutant construct

   PMID:34790172

   Open questions at the time

   • Single case with limited mechanistic detail; not independently confirmed
   • Connection between active-zone scaffolding function and angiogenesis unexplained
   • No in vivo model of the mutation

• How ERC2's calcium-channel anchoring, syntenin-1/PDZ organization, and SRPK2-regulated oligomerization are coordinated dynamically to set release probability remains unresolved.
• No integrated structural model of the ERC2–VDCC–Bassoon/Piccolo cytomatrix
• Temporal order of phosphorylation, oligomerization, and channel recruitment unknown
• Direct effect of ERC2 manipulation on neurotransmitter release kinetics not established in the corpus