Characterization of a KCNB1 variant associated with autism, intellectual disability, and epilepsy

(A) Location of the I199F variant mapped onto the crystal structure of a K_V2.1/K_V1.2 chimera (PDB 29R9).¹⁰ A channel tetramer is shown. I199F (magenta) lies in the S1 transmembrane segment of the voltage-sensing domain. (B) KCNB1-I199F is expressed and trafficked to the cell surface. Cell-surface expression was measured using cell-surface biotinylation of CHO-K1 cells transfected with wild-type (WT) or mutant K_V2.1. Total (5 μg per lane) and surface fractions of K_V2.1 were detected with the anti-K_V2.1 antibody. Endogenous TfR levels were measured as a loading control. Calnexin was present in total cell lysates, but not surface fraction, demonstrating selective biotinylation of extracellular proteins. The blot shown is representative of 3 independent experiments. (C) Current-voltage relationships measured for KCNB1-I199F (n = 74) and WT homotetrameric channels (n = 185). (D) Voltage dependence of activation and inactivation curves calculated for KCNB1-I199F (n = 23) and WT (n = 63) homotetrameric channels. (E) Current-voltage relationships measured for KCNB1-I199F (n = 40) and WT (n = 27) heterotetrameric channels. (F) Voltage dependence of activation and inactivation curves calculated for KCNB1-I199F (n = 31) and WT (n = 26) heterotetrameric channels.