RIMBP2

RIMBP2 is a multidomain presynaptic active zone scaffold that couples voltage-gated Ca2+ channels to the synaptic vesicle release machinery, controlling Ca2+ channel topography and abundance, vesicle docking and priming, release probability, and fast vesicle replenishment (PMID:27671655, PMID:34353898, PMID:38329474). It binds the C-terminal tail of CaV2.1 directly and organizes the clustering and abundance of P/Q-type channels at active zones, with channel recruitment being mechanistically separable from fusion competence (PMID:38329474, PMID:28510727); superresolution imaging in knockout neurons shows degraded CaV2.1 topography accompanied by reduced initial release probability and enhanced short-term facilitation (PMID:27671655, PMID:34353898). Its actions are synapse-type-specific: at hippocampal mossy fiber terminals it promotes docking/priming by stabilizing Munc13-1 at the active zone, whereas at CA3-CA1 synapses it primarily affects Ca2+-secretion coupling (PMID:31535974). In the cochlea RIMBP2 positively sets the number of synaptic CaV1.3 channels at inner hair cell active zones, supports readily releasable pool exocytosis and fast vesicle replenishment, and is required for outer hair cell survival, such that its loss produces synaptopathic hearing impairment (PMID:29163046, PMID:33867935, PMID:40880039). Beyond neuronal and sensory synapses, RIMBP2 serves as a physical scaffold linking exophilin-8 to myosin-VIIa, CaV1.3, RIM, and Munc13-1 to drive peripheral granule accumulation and exocytosis in pancreatic β-cells (PMID:28673385). RIMBP2 is transcriptionally controlled by TCF4, and its loss is the principal mediator of presynaptic and network deficits in TCF4-mutant Pitt-Hopkins syndrome neurons, where re-expressing RIMBP2 rescues synaptic transmission (PMID:37573005).

1. 2016 High

   Established RIMBP2 as the dominant isoform setting release probability by organizing CaV2.1 clustering at hippocampal active zones, defining its core function in Ca2+ channel-release coupling.

   Evidence RIM-BP2 KO mice with patch-clamp electrophysiology and superresolution imaging of CaV2.1 in hippocampal cultures and slices

   PMID:27671655

   Open questions at the time

   • Did not resolve which RIMBP2 domains mediate channel clustering
   • Did not address synapse-type specificity
2. 2017 High

   Extended RIMBP2 function to sensory synapses, showing it positively controls CaV1.3 channel number and fast vesicle replenishment at inner hair cell ribbon synapses without altering Ca2+-exocytosis coupling for the RRP.

   Evidence Constitutive RIM-BP2 KO mice with STED, electron tomography, patch-clamp, Ca2+ imaging, and ABR recordings

   PMID:29163046

   Open questions at the time

   • Mechanism of replenishment support unresolved
   • Did not test redundancy with RIM-BP1
3. 2017 High

   Defined a molecular partner architecture, identifying RIMBP2 as a direct binding partner of exophilin-8 that scaffolds myosin-VIIa, CaV1.3, RIM, and Munc13-1 to drive granule exocytosis in a non-neuronal secretory cell.

   Evidence Reciprocal co-immunoprecipitation, knockdown/knockout of complex components, and exocytosis assays in pancreatic β-cells/islets

   PMID:28673385

   Open questions at the time

   • Binding interfaces and stoichiometry not mapped
   • Whether the same complex operates at neuronal synapses untested
4. 2017 Medium

   Pinpointed the CaV2.1 C-terminal tail as the direct interaction site for RIMBP2 and showed alternative splicing weakens this interaction, linking it to ataxia and seizure phenotypes.

   Evidence CaV2.1 C-terminal splice-site knockin mice with co-immunoprecipitation from cerebellar tissue

   PMID:28510727

   Open questions at the time

   • Focused on the CaV2.1 side; RIMBP2 binding residues not defined
   • Single lab
5. 2019 High

   Revealed synapse-type-specific diversification, showing RIMBP2 stabilizes Munc13-1 to promote docking/priming at mossy fibers but only mildly affects Ca2+-secretion coupling at CA3-CA1 synapses.

   Evidence RIM-BP2 KO mice with electrophysiology, Munc13-1 immunofluorescence, and electron microscopy across two synapse types

   PMID:31535974

   Open questions at the time

   • Molecular basis for Munc13-1 stabilization unresolved
   • What determines synapse-type specificity unknown
6. 2021 High

   Demonstrated at the endbulb of Held that RIMBP2 organizes CaV2.1 topography and SV tethering/docking required for high initial release probability and fast replenishment, with in vivo consequences for sound onset signaling.

   Evidence RIM-BP2 KO mice with superresolution and electron microscopy, patch-clamp, and in vivo auditory physiology

   PMID:34353898

   Open questions at the time

   • Did not separate tethering from docking mechanisms
   • Channel-vesicle distance relationship not directly measured
7. 2021 High

   Established genetic redundancy in the cochlea, showing combined RIM-BP1/2 loss produces RRP exocytosis deficits and hearing impairment exceeding RIM-BP2 alone, while Ca2+ influx reduction is shared.

   Evidence RIM-BP1/2 double KO mice with ABR, otoacoustic emissions, and IHC patch-clamp, compared to single KO

   PMID:33867935

   Open questions at the time

   • Whether RIM-BP1/2 redundancy applies at central synapses untested
   • Distinct molecular roles of the two isoforms unresolved
8. 2023 High

   Placed RIMBP2 downstream of TCF4 in a disease pathway, identifying it as the most downregulated gene in Pitt-Hopkins syndrome neurons and showing presynaptic re-expression rescues synaptic and network deficits.

   Evidence iPSC-derived cortical neurons from PTHS patients with RNA-seq, electrophysiology, Ca2+ imaging, multielectrode arrays, and RIMBP2 overexpression rescue (peer-reviewed plus preceding bioRxiv preprint)

   PMID:36712024 PMID:37573005

   Open questions at the time

   • Whether TCF4 binds the RIMBP2 promoter directly not established
   • Mechanism by which RIMBP2 loss alters network excitability incomplete
9. 2024 High

   Distinguished RIMBP2's role in Ca2+ channel recruitment from its role in fusion competence at mossy fiber terminals using direct presynaptic recordings.

   Evidence RIM-BP2 KO mice with direct presynaptic patch-clamp capacitance recording, EPSC recordings, and STED microscopy

   PMID:38329474

   Open questions at the time

   • Molecular basis of the fusion-competence defect unresolved
   • How the two functions are domain-encoded unknown
10. 2024 Low

    Proposed a non-neuronal role in cancer, where RIMBP2 is an m6A-stabilized IGF2BP2 target promoting HNSCC proliferation and radioresistance via ER stress.

    Evidence IGF2BP2/RIMBP2 functional studies in HNSCC cell lines and in vivo with m6A reader binding assays

    PMID:39653741

    Open questions at the time

    • Mechanistic chain from RIMBP2 to ER stress partially inferred from a single lab
    • RIMBP2's own molecular activity in this context undefined
11. 2025 Medium

    Provided a mechanical model in which RIMBP2 executes an actin-powered crane-like conformational rotation to drive vesicles toward the membrane, with its N-terminus transmitting actin-derived force.

    Evidence FRET-based conformational biosensors with RIM-BP2 mutagenesis and cytoskeletal/membrane perturbation in cortical neurons and SH-SY5Y cells

    PMID:40999007

    Open questions at the time

    • Single lab using engineered biosensors
    • Direct structural confirmation of the rotation lacking
    • Physiological force magnitudes not measured
12. 2025 High

    Expanded cochlear function to include outer hair cell survival alongside IHC RRP, sustained release, and fast endocytosis, broadening RIMBP2's role beyond Ca2+-release coupling.

    Evidence Rimbp2 KO mice with ABR, IHC patch-clamp, immunofluorescence, and TUNEL apoptosis assays

    PMID:40880039

    Open questions at the time

    • Mechanism linking RIMBP2 loss to OHC apoptosis unknown
    • Whether the endocytosis role is direct or secondary unresolved

• How RIMBP2's distinct molecular activities — Ca2+ channel recruitment, Munc13-1 stabilization, fusion competence, and actin-driven vesicle transport — are partitioned across its domains and tuned to specific synapse types remains unresolved.
• No domain-resolved structure-function map across synapse types
• Molecular basis of synapse-type-specific specialization unknown
• Direct structural data for the proposed conformational cycle absent