Fig 4. Schematic drawings showing domain composition (A) and topology in the plasma membrane of a SLO-1 subunit (B).

The scheme in (A) is drawn to scale based on Onchocerca volvulus SLO-1a (GenBank accession number: MW039265; the protein contains 7 transmembrane domains. The transmembrane domains S2–S4 contain charged amino acids and function as voltage sensor, while S5 and S6 are involved in building the pore. For this purpose, 4 subunits form a tetramer. The P loop is involved in tetramer formation and pore building. The 2 RCK domains and the Ca²⁺ bowl are involved in regulation of conductance by intracellular Ca²⁺ levels. P loop, pore-forming loop; PM, plasma membrane; RCK, regulator of potassium conductance; SLO-1, slowpoke big K⁺ conductance channel.