Dimer of full-length cGMP-bound Bd1971; one monomer coloured individually by subdomain, the opposing monomer coloured white. Ligand represented in stick form, EAL active site Mg2+ as green sphere. View from top of that in (A), detailing EAL region of dimer interface. View from opposing side, detailing C-helix dimer interface at cNMP domain. The Bd1971 EAL dimerization interface (purple, white) matches that of a canonical, active dimer from the well-characterized T. denitrificans EAL (tan, PDB 2r6o); the catalytic Asp pairs of the two enzymes adopt a similar conformation (stick form, D306/307 from Bd1971, D646/647 from 2r6o). Structure of the cyclic-di-GMP bound complex of Bd1971 (ligand C represented in yellow, bound Ca2+ ions as green spheres). Residues R182, R330 and Y385 display the largest shift between the apoenzyme (tan) and bound (blue) states, R182 complexing the cyclic-di-GMP phosphate, and Y385 stacking with a guanine base. 