Three-dimensional structure of Ito:: Kv4.2-KChIP2 ion channels by electron microscopy at 21 Å resolution

Regulatory KChlP2 subunits assemble with pore-forming Kv4.2 subunits in 4:4 complexes to produce native voltage-gated potassium (Kv) channels like cardiac It, and neuronal I-A subtypes. Here, negative stain electron microscopy (EM) and single particle averaging reveal KChlP2 to create a novel similar to35 x 115 x 115 Angstrom, intracellular fenestrated rotunda: four peripheral columns that extend down from the membrane-embedded portion of the channel to enclose the Kv4.2 hanging gondola (a platform held beneath the transmembrane conduction pore by four internal columns). To reach the pore from the cytosol, ions traverse one of four external fenestrae to enter the rotundal vestibule and then cross one of four internal windows in the gondola.