RIM1 is a member of the RIM superfamily of proteins (Rim1-4). These genes express seven known RIM isoforms: RIM1α, 1β; RIM2α, 2β, 2γ; and RIM3γ and RIM4γ which serve as scaffolding proteins in presynaptic nerve terminals by interacting with several other protein components localized at the active zone, including Munc13, ELKS (or CAST), liprins and voltage-gated Ca²⁺ channels (VGCCs). RIM1 directly binds to the C-terminal regions of the α₁ subunit of N- and P/Q-type calcium channels, and can also interact with the β auxiliary subunit of P/Q-type calcium channels^1-3_.

RIM proteins were found to be required for normal Ca²⁺ triggering of exocytosis. This interaction with Ca²⁺ channel significantly slows channel inactivation resulting in increased Ca²⁺ influx during action potentials.

Deficiency of RIM1 decreases presynaptic Ca²⁺ channel density. RIM proteins are involved in neurotransmitter release and contribute to long- and short-term synaptic plasticity.