Membrane topology of a Kv subunit showing SCA13 mutations. The cartoon has been marked to indicate the approximate locations of the R335H and F363L mutations. The S1-S6 transmembrane segments, the re-entrant pore (P) loop, and the amino and carboxyl termini are labeled. Brackets denote the voltage sensor domain (S1-S4) and pore region (S5-P-S6). Circled plus signs in S4 indicate positively-charged arginine residues that sense voltage [35, 36]. The third circle contains an H denoting the R335H mutation. Circled L in S5 indicates the location of the F363L mutation.