Structural Dynamics Of Slow-Inactivation In A Voltage-Gated Sodium Channel

Slow-inactivation in voltage-gated sodium channels (NaV) directly regulates excitability of neurons, cardiac myocytes, and skeletal muscles. Although NaV slow-inactivation appears to be conserved across the phylogeny, from bacteria to humans, the structural basis for this mechanism remains unclear. Using X-ray crystallography, in combination with spin-labeling/EPR spectroscopic measurements in membrane reconstituted prokaryotic NaV homologues, we characterize the conformational dynamics of the selectivity filter region in the conductive and slow-inactivated states to determine the molecular events underlying NaV gating. Our findings reveal profound conformational flexibility of the pore in the slow-inactivated state. We find that the P1 and P2 pore-helices undergo opposing movements with respect to the pore-axis, resulting in changes in volume of both the central, as well as the intersubunit cavities. These regions form pathways for lipophilic drugs that modulate slow-inactivation; hence, our findings provide novel insights into the molecular basis for state-dependent effects of these drugs on channel function.