Schematic showing the structures of the membrane-embedded region of the protein TMEM120A. This region of the protein is comprised of two monomers, both of which contain six helical segments (blue cylinders) that span across the lipid bilayer (pale yellow and gray). When a coenzyme called CoASH (yellow) is present, it binds to a site inside the helical segments (left). When CoASH is not present (right), two of the cytoplasmic loops (orange) that connect helical segments change their position to cover the entrance to the binding site. Cytoplasmic loops that do not change their position are not shown.