Structural characterization reveals that a PilZ domain protein undergoes substantial conformational change upon binding to cyclic dimeric guanosine monophosphate

PA4608 is a single PilZ domain protein from Pseudomonas aeruginosa that binds to cyclic dimeric guanosine monophosphate (c‐di‐GMP). Although the monomeric structure of unbound PA4608 has been studied in detail, the molecular details of c‐di‐GMP binding to this protein are still uncharacterized. Hence, we determined the solution structure of c‐di‐GMP bound PA4608. We found that PA4608 undergoes conformational changes to expose the c‐di‐GMP binding site by ejection of the C‐terminal 310 helix. A dislocation of the C‐terminal tail in the presence of c‐di‐GMP implies that this region acts as a lid that alternately covers and exposes the hydrophobic surface of the binding site. In addition, mutagenesis and NOE data for PA4608 revealed that conserved residues are in contact with the c‐di‐GMP molecule. The unique structural characteristics of PA4608, including its monomeric state and its ligand binding characteristics, yield insight into its function as a c‐di‐GMP receptor.