State transitions of VSD in a µs-scale MD simulation. The dynamic behavior of VSD_II under an external electric field of 500 mV in opposite directions. Traces of z positions for Cα atoms of the gating-charge residues (R1-K5) in different colors in VSD_II relative to the HCS are shown to track the structural changes. Molecular images of representative VSD_II snapshots (0, 3, 6, 9, and 13 µs) are presented in a white ribbon representation, with licorice representations of gating charges (blue), countercharges (red), and the HCS (green). The direction and magnitude of the external electric field applied are depicted by arrows (blue and green).