Figure 1.

Two-dimensional model of the Na⁺/Ca²⁺ exchanger (NCX1). The extracellular surface is on top and shown are 9 TMSs. The α repeat regions (α-1 and α-2), critical for transport, are in black. The XIP region is involved in autoregulation and binds PIP₂. The two Ca²⁺-binding domains (CBD1 and CBD2) regulate exchange activity. The structures of CBD1 and CBD2 are known and are shown as ribbon diagrams as determined by X-ray crystallography. Green balls represent bound Ca²⁺.