The production of the PEL polysaccharide inPseudomonas aeruginosarequires the binding of bis-(3′,5′)-cyclic dimeric guanosine monophosphate (c-di-GMP) to the cytoplasmic GGDEF domain of the inner membrane protein PelD. Here, the overexpression, purification and crystallization of a soluble construct of PelD that encompasses the GGDEF domain and a predicted GAF domain is reported. Diffraction-quality crystals were grown using the hanging-drop vapour-diffusion method. The crystals grew as flat plates, with unit-cell parametersa = 88.3,b= 114.0,c= 61.9 Å, α = β = γ = 90.0°. The PelD crystals exhibited the symmetry of space groupP21212 and diffracted to a minimumd-spacing of 2.2 Å. On the basis of the Matthews coefficient (VM= 2.29 Å3 Da−1), it was estimated that two molecules are present in the asymmetric unit.
