Structure of chicken bestrophin-1. The overall structure is shown as viewed (a) from the plane of the membrane and (b) from the outside of the cell. Each of the five subunits are identical and a single subunit is coloured green for clarity. Approximate boundaries of the membrane are indicated. Calcium ions are represented by cyan spheres. (c) Coordination in the Ca2+-clasp is shown including a coordinated water molecule (red sphere).