An active zone state switch concentrates and immobilizes voltage-gated Ca2+ channels to promote long-term plasticity

Abstract A molecularly diverse spectrum of plasticity mechanisms orchestrates brain information processing and storage via positive (“Hebbian”) and negative (“homeostatic”) feedbacks, which, however, mechanistically converge and functionally interact in vivo. The presynaptic scaffold proteins that orchestrate active zone (AZ) function undergo plastic remodeling to regulate release potentiation. Here, voltage-gated Ca2+ channel function and their exact AZ nanoscale distribution steer release, although how they are involved in AZ remodeling remains unknown. We here establish intravital, dynamic, single-molecule imaging of endogenously tagged Ca2+ channel Cacophony (Cac) at Drosophila AZs triggered towards homeostatic potentiation. At potentiating AZs, Cac channel numbers increased, and their mobility decreased, while their overall distribution compacted. Mechanistically, RIM-1 and RimBP proteins and their conserved bindings sites, within the Cac channel’s C-terminus, were dispensable for Cac immobilization and compaction. Conversely, the absence of ELKS-family homolog Bruchpilot precluded Cac immobilization and compaction. We show that AZs can undergo a state switch, likely via the ELKS scaffold to concentrate and immobilize Ca2+ channels and thus boost release.