Structure of the Periplasmic Stress Response Protein CpxP

Abstract

CpxP is a novel bacterial periplasmic protein with no homologues of known function. In Gram-negative enteric bacteria, CpxP is thought to interact with the two-component sensor kinase, CpxA, to inhibit induction of the Cpx envelope stress response in the absence of protein misfolding. CpxP has also been shown to facilitate DegP-mediated proteolysis of misfolded proteins. Six mutations that negate the ability of CpxP to function as a signaling protein are localized in or near two conserved LTXXQ motifs that define a class of proteins with similarity to CpxP, Pfam PF07813. To gain insight into how these mutations might affect CpxP signaling and/or proteolytic adaptor functions, the crystal structure of CpxP from Escherichia coli was determined to 2.85-Å resolution. The structure revealed an antiparallel dimer of intertwined ␣-helices with a highly basic concave surface. Each protomer consists of a long, hooked and bent hairpin fold, with the conserved LTXXQ motifs forming two diverging turns at one end. Biochemical studies demonstrated that CpxP maintains a dimeric state but may undergo a slight structural adjustment in response to the inducing cue, alkaline pH. Three of the six previously characterized cpxP loss-of-function mutations, M59T, Q55P, and Q128H, likely result from a destabilization of the protein fold, whereas the R60Q, D61E, and D61V mutations may alter intermolecular interactions.

Resistance and survival strategies of Salmonella enterica to environmental stresses

“…Under noninducing conditions, CpxP is bound to the sensor-kinase CpxA inhibiting its kinase activity and preventing phosphorylation of the response regulator CpxR. When conditions exist that lead to the accumulation of misfolded and/or aggregated proteins in the periplasm, CpxP releases from CpxA and/or is degraded by the DegP protease (Thede et al, 2011). This then allows CpxA to autophosphorylate itself and then transfer the phosphoryl group to a conserved aspartate in the receiver domain of CpxR forming CpxR-P. CpxR-P acts as a transcriptional regulator acting to up-regulate or down-regulate the genes mentioned above (MacRitchie et al, 2008;Rowley et al, 2006).…”

Sinorhizobium meliloti ExoR Is the Target of Periplasmic Proteolysis

“…The example that is closest to S. meliloti ExoR is the function and regulation of the E. coli periplasmic adaptor protein, CpxP, which is involved in sensing pH variations to regulate membrane lipid composition (9,26,40,54). The CpxP protein interacts with and inhibits the periplasmic sensing domain of the CpxA protein, the sensor of the CpxA/CpxR twocomponent system (14,46,54,56). The periplasmic serine protease DegP is activated by general envelope disruptions, including pH changes, and cleaves the CpxP protein, thereby removing CpxP from the CpxA sensor (26).…”

The Cpx Stress Response System Potentiates the Fitness and Virulence of Uropathogenic Escherichia coli

“…UTI89 is apparently more dependent upon one or more of these activities when challenged with complement, whereas CFT073 can make do without CpxP. It is feasible that structural homologues of CpxP, such as Spy and ZraP (92)(93)(94), can substitute for CpxP under specific conditions in strains like CFT073. The Cpx system is best known for its effects on the expression of periplasmic chaperones and proteases in response to envelope stress, and the misregulation of these and other factors likely contribute to the myriad defects observed with the ⌬cpxP and ⌬cpxRA mutants in our assays.…”

“…tion as a periplasmic chaperone and may act as a sensor for metal ions, like zinc and copper (43,44,91,92). UTI89 is apparently more dependent upon one or more of these activities when challenged with complement, whereas CFT073 can make do without CpxP.…”