Crystallization

Crystals were grown at 17°C by vapor diffusion in 0.6 + 0.6 µl hanging drops with a reservoir containing 42–46% polyethylene glycol 400, 100–200 mM MgCl₂ and 100 mM Mops, pH 7.4. Cubic crystals, with a final size around 100 × 100 × 100 μm, were obtained after 1–3 d of crystal growth.

For anomalous experiments to confirm the Cl⁻ site, crystals were grown using an identical protocol, but exchanging the reservoir solution MgCl₂ to MgBr₂, before mixing the 0.6 + 0.6 µl drop.