a, 2Fo-Fc electron density of TM-1, -3, -8. The density is contoured at 1.5 σ. b, Crystal packing of BicATM. The crystal is of space group P2 and contains two molecules (colored in yellow and magenta) in the asymmetric unit. c, Fo-Fc electron densities of HCO3- and the metal ion (contoured at 2.0 σ). d, 2Fo-Fc electron density of monoolein (contoured at 1.0 σ).