PMID: 22605337

Authors:

Whitney JC, Colvin KM, Marmont LS, Robinson H, Parsek MR, Howell PL

Title:

Structure of the cytoplasmic region of PelD, a degenerate diguanylate cyclase receptor that regulates exopolysaccharide production in Pseudomonas aeruginosa.

Journal:

J Biol Chem. 2012 May 17.

Abstract:

High cellular concentrations of bis-(3('),5('))-cyclic dimeric guanosine mono-phosphate (c-di-GMP) regulate a diverse range of phenotypes in bacteria including biofilm development. The opportunistic pathogen, Pseudomonas aeruginosa, produces the PEL polysaccharide to form a biofilm at the air-liquid interface of standing cultures. Among the proteins required for PEL polysaccharide production, PelD has been identified as a membrane bound c-di-GMP specific receptor. In this work, we present the X-ray crystal structure of a soluble cytoplasmic region of PelD in its apo and c-di-GMP complexed forms. The structure of PelD reveals an N-terminal GAF domain and a C-terminal degenerate GGDEF domain, the latter of which binds dimeric c-di-GMP at an RXXD motif that normally serves as an allosteric inhibition site for active diguanylate cyclases. Using isothermal titration calorimetry we demonstrate that PelD binds c-di-GMP with low micromolar affinity and that mutation of residues involved in binding not only decreases the affinity of this interaction but also results in several PEL specific phenotypes in vivo. Bioinformatics analysis of the juxtamembrane region of PelD suggests that it contains an alpha-helical stalk region that connects the soluble region to the transmembrane domains and that similarly to other GAF domain containing proteins, this region likely forms a coiled-coil motif that mediates dimerization. PelD along with Alg44 and BcsA of the alginate and cellulose secretion systems, respectively, collectively constitute a group of c-di-GMP receptors that appear to regulate exopolysaccharide assembly at the protein level through activation of their associated glycosyl transferases.