Structural basis for modulation of human Na_V1.3 by clinical drug and selective antagonist

Voltage-gated sodium (Na_V) channels play fundamental roles in initiating and propagating action potentials. Na_V1.3 is involved in numerous physiological processes including neuronal development, hormone secretion and pain perception. Here we report structures of human Na_V1.3/β1/β2 in complex with clinically-used drug bulleyaconitine A and selective antagonist ICA121431. Bulleyaconitine A is located around domain I-II fenestration, providing the detailed view of the site-2 neurotoxin binding site. It partially blocks ion path and expands the pore-lining helices, elucidating how the bulleyaconitine A reduces peak amplitude but improves channel open probability. In contrast, ICA121431 preferentially binds to activated domain IV voltage-sensor, consequently strengthens the Ile-Phe-Met motif binding to its receptor site, stabilizes the channel in inactivated state, revealing an allosterically inhibitory mechanism of Na_V channels. Our results provide structural details of distinct small-molecular modulators binding sites, elucidate molecular mechanisms of their action on Na_V channels and pave a way for subtype-selective therapeutic development.