G protein-gated inhibitory module of N-type (CaV2.2) Ca2+ channels

Voltage-dependent G protein (Gp gamma) inhibition of N-type (Ca(v)2.2) channels supports presynaptic inhibition and represents a central paradigm of channel modulation. Still controversial are the proposed determinants for such modulation, which reside on the principal alpha(1B) channel subunit. These include the interdomain I-II loop (I-II), the carboxy tail (CT), and the amino terminus (NT). Here, we probed these determinants and related mechanisms, utilizing compound-state analysis with yeast two-hybrid and mammalian cell FRET assays of binding among channel segments and G proteins. Chimeric channels confirmed the unique importance of NT. Binding assays revealed selective interaction between NT and I-II elements. Coexpressing NT peptide with Gp gamma induced constitutive channel inhibition, suggesting that the NT domain constitutes a G protein-gated inhibitory module. Such inhibition was limited to NT regions interacting with I-II, and G-protein inhibition was abolished within (alpha(1B) channels lacking these NT regions. Thus, an NT module, acting via interactions with the I-II loop, appears fundamental to such modulation.