| Bassoon (BSN), a multi-domain presynaptic cytomatrix protein of the active zone, forms part of the core scaffold alongside Piccolo that anchors neurotransmitter release machinery at excitatory synapses, enabling structural integrity and dynamic vesicle management. Its modular architecture, featuring zinc-finger motifs, coiled-coil regions, and polyglutamine stretches, facilitates extensive protein-protein interactions within the cytomatrix, positioning it near synaptic vesicle clusters and voltage-gated calcium channels to orchestrate release site organization. Bassoon regulates synaptic vesicle (SV) pools by modulating presynaptic phosphorylation networks, particularly through CDK5-dependent control of PDE4 activity, which fine-tunes cAMP/PKA signaling; this pathway governs synapsin I and SNAP-25 phosphorylation, promoting the transition of vesicles from resting to readily releasable pools (RRP) and enhancing reloading efficiency during high-frequency stimulation. It also maintains SV clustering redundantly with Piccolo, preventing dispersal post-exocytosis, while coordinating endocytosis and proteostasis via ubiquitin-related pathways, ensuring sustained transmitter release competence at glutamatergic synapses in central neurons. Bassoon is critical for short-term synaptic plasticity and high-fidelity neurotransmission, making it a prime target for dissecting vesicle dynamics in neuronal circuits or optogenetic manipulations of release probability. Dysregulation through BSN mutations disrupts these processes, contributing to neurodegeneration in disorders like progressive supranuclear palsy, multiple system atrophy, epilepsy, and schizophrenia, often via impaired proteostasis or vesicle tethering. In ribbon synapses of sensory neurons, Bassoon uniquely sustains continuous exocytosis by linking SVs to calcium channels, while its developmental role influences axon terminal maturation. |
