1.A.46.2.8
Functionally characterized bestrophin homologue, KpBEST, YneE or RFP-TM of 305 aas and 3 or 4 TMSs per subunit.  KpBest is a pentamer that forms a five-helix transmembrane pore, closed by three rings of conserved hydrophobic residues, and has a cytoplasmic cavern with a restricted exit (Yang et al. 2014). From electrophysiological analysis of structure-inspired mutations in KpBest and hBest1, a sensitive control of ion selectivity was observed in the bestrophins, including reversal of anion/cation selectivity, and dramatic activation by mutations at the cytoplasmic exit.  The wild type protein seems to be a cation (Na⁺) channel but the I66F mutation changed it into an anion (Cl^-) channel (Yang et al. 2014).  There are two  constrictions in the channel, one provides the ion selectivity and the other serves as the gate.