1.A.1.21.1
K⁺- and Na⁺-conducting NaK channel, NaK2K of 97 aas and 2 TMSs. The 3-D structure has been solved with Na⁺ and K⁺bound (Shi et al., 2006).  It exhibits tight structural and dynamic coupling between the selectivity filter and the channel scaffold (Brettmann et al. 2015). A hydrophobic residue at the bottom of the selectivity filter, Phe92, appears in dual conformations. One of the two conformations of Phe92 restricts the diameter of the exit pore around the selectivity filter, limiting ion flow through the channel, while the other conformation of Phe92 provides a larger-diameter exit pore from the selectivity filter. Thus, Phe92 acts as a hydrophobic gate (Langan et al. 2020).