Figure 1.

Topology of a plant Two-Pore Cation Channel 1 (TPC1). A TPC1-subunit is built of two concatenated copies of a structural 6-TM motif, each with six transmembrane domains (1–6). The cytosolic linker between them contains two EF-hands, which sense the cytosolic Ca²⁺ concentration. Two subunits assemble into a functional channel and form a central permeation pathway.