Structural Analysis of the GGDEF-EAL Domain-Containing c-di-GMP Receptor FimX

Abstract

Summary Bacterial pathogenesis involves social behavior including biofilm formation and swarming, processes that are regulated by the bacterially unique second messenger cyclic di-GMP (c-di-GMP). Diguanylate cyclases containing GGDEF and phosphodiesterases containing EAL domains have been identified as the enzymes controlling cellular c-di-GMP levels, yet less is known regarding signal transmission and the targets of c-di-GMP. FimX, a protein from Pseudomonas aeruginosa that governs twitching motility, belongs to a large subfamily containing both GGDEF and EAL domains. Biochemical and structural analyses reveals its function as a high-affinity receptor for c-di-GMP. A model for full-length FimX was generated combining solution scattering data and crystal structures of the degenerate GGDEF and EAL domains. While FimX forms a dimer in solution via the N-terminal domains, a crystallographic EAL domain dimer suggests modes for the regulation of FimX by c-di-GMP binding. The results provide the structural basis for c-di-GMP sensing via degenerate phosphodiesterases.

Structure of the Cyanobacterial Phytochrome 2 Photosensor Implies a Tryptophan Switch for Phytochrome Signaling

“…For example, FimX from Pseudomonas aeruginosa, a twitching motility regulator, also carries GGDEF-EAL domains. Here, the overall quaternary organization corresponds to an elongated antiparallel dimer, where the GGDEF-EAL modules are not involved in dimerization (38). Such an arrangement of the photosensory SynCph2(1-2) module may be of physiological relevance for signaling toward the GGDEF*-EAL module.…”

Binding of Cyclic Diguanylate in the Non-catalytic EAL Domain of FimX Induces a Long-range Conformational Change

“…binding of c-di-GMP by FimX does not induce a change in global structure or oligomeric state because the free and c-di-GMP-bound FimX proteins appear to be almost identical in solution scattering and analytic ultracentrifugation analysis (18). We postulated that the effect of c-di-GMP binding might be exerted through a local conformational change that was undetectable by the scattering and sedimentation methods.…”

“…FimX is a cytoplasmic protein (76 kDa) required for normal twitching motility and biofilm formation in the opportunistic pathogen Pseudomonas aeruginosa (16,17). Although the EAL domain of FimX was first suggested to function as a phosphodiesterase domain, it was later established to be a non-catalytic domain (7,16,18). Recent studies from Sondermann and co-workers (18) have demonstrated that the EAL domain of P. aeruginosa FimX binds c-di-GMP with high affinity.…”

“…Although the EAL domain of FimX was first suggested to function as a phosphodiesterase domain, it was later established to be a non-catalytic domain (7,16,18). Recent studies from Sondermann and co-workers (18) have demonstrated that the EAL domain of P. aeruginosa FimX binds c-di-GMP with high affinity. The crystal structure of the stand-alone EAL domain in complex with c-di-GMP determined by the same group reveals the binding of c-di-GMP without the assistance of metal ion.…”

Global Regulatory Pathways and Cross-talk ControlPseudomonas aeruginosaEnvironmental Lifestyle and Virulence Phenotype

“…Consistent with this hypothesis, mutation of the GGDEF domain in FimX, abolishes GTP binding and stimulation of PDE activity (Kazmierczak, 2006). However, recent structural studies indicate that the degenerate GGDEF domain of FimX is incapable of nucleotide binding, while the EAL domain binds c-di-GMP with high affinity inducing a conformational change that may impede FimX binding to its putative partner located at the bacterial pole to regulate Tfp production and twitching motility (Navarro, 2010;Qi, 2011).…”