Family Report for: CFTR-inhibitory-factor_Cif

The Gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that secretes a multitude of virulence factors during the course of infection. Among these is Cif, an epoxide hydrolase (EH) that reduces the functional localization of the cystic fibrosis transmembrane conductance regulator in epithelial cells. In addition to being the first reported EH virulence factor, Cif possesses unique sequence deviations from canonical EH motifs. Foremost among these is the substitution of a histidine for the first epoxide ring-opening tyrosine in the active site. To test the functional equivalence of Tyr and His side chains at this position, we have generated the mutant Cif-H177Y. Structural analysis confirms that both the WT His and mutant Tyr side chains can be accommodated without large-scale conformational changes. However, the Tyr mutant is functionally inactive. Based on a detailed analysis of the structure of the Tyr mutant, it appears that Cif's main-chain conformation imposes a functional requirement for a His at this position. Comparison with canonical EH structures reveals additional conformational differences, which are coupled to divergent sequence characteristics. When used to probe the genomes of other opportunistic pathogens, these sequence-structure criteria uncover candidate sequences that appear to form a distinct subfamily of Cif-like epoxide hydrolases characterized by a conserved His/Tyr ring-opening pair.

The opportunistic pathogen Pseudomonas aeruginosa secretes a protein that triggers the accelerated degradation of the cystic fibrosis transmembrane conductance regulator (CFTR) in airway epithelial cells. This protein, which is known as the CFTR inhibitory factor (Cif), acts as a virulence factor and may facilitate airway colonization by P. aeruginosa. Based on sequence similarity Cif appears to be an epoxide hydrolase (EH), but it lacks several of the conserved features found in the active sites of canonical members of the EH family. Here, the crystallization of purified recombinant Cif by vapor diffusion is reported. The crystals formed in space group C2, with unit-cell parameters a = 167.4, b = 83.6, c = 88.3 A, beta = 100.6 degrees . The crystals diffracted to 2.39 A resolution on a rotating-anode source. Based on the calculated Matthews coefficient (2.2 A(3) Da(-1)), it appears that the asymmetric unit contains four molecules.

Cystic fibrosis transmembrane conductance regulator (CFTR) inhibitory factor (Cif) is a virulence factor secreted by Pseudomonas aeruginosa that reduces the quantity of CFTR in the apical membrane of human airway epithelial cells. Initial sequence analysis suggested that Cif is an epoxide hydrolase (EH), but its sequence violates two strictly conserved EH motifs and is also compatible with other alpha/beta hydrolase family members with diverse substrate specificities. To investigate the mechanistic basis of Cif activity, we have determined its structure at 1.8 A resolution by X-ray crystallography. The catalytic triad consists of residues Asp129, His297, and Glu153, which are conserved across the family of EHs. At other positions, sequence deviations from canonical EH active-site motifs are stereochemically conservative. Furthermore, detailed enzymatic analysis confirms that Cif catalyzes the hydrolysis of epoxide compounds, with specific activity against both epibromohydrin and cis-stilbene oxide, but with a relatively narrow range of substrate selectivity. Although closely related to two other classes of alpha/beta hydrolase in both sequence and structure, Cif does not exhibit activity as either a haloacetate dehalogenase or a haloalkane dehalogenase. Reassessment of the structural and functional consequences of the H269A mutation suggests that Cif's effect on host-cell CFTR expression may require hydrolysis of an extended endogenous epoxide substrate.

The CFTR inhibitory factor (Cif) is an epoxide hydrolase (EH) virulence factor secreted by the bacterium Pseudomonas aeruginosa. Sequence alignments reveal a pattern of Cif-like substitutions that proved to be characteristic of a new subfamily of bacterial EHs. At the same time, crystallographic and mutagenetic data suggest that EH activity is required for virulence and that Cif's active site remains generally compatible with a canonical two-step EH mechanism. A hallmark of this mechanism is the formation of a covalent hydroxyalkyl-enzyme intermediate by nucleophilic attack. In several well-studied EHs, this intermediate has been captured at near stoichiometric levels, presumably reflecting rate-limiting hydrolysis. Here we show by mass spectrometry that only minimal levels of the expected intermediate can be trapped with WT Cif. In contrast, substantial amounts of intermediate are recovered from an active-site mutant (Cif-E153Q) that selectively targets the second, hydrolytic release step. Utilizing Cif-E153Q and a previously reported nucleophile mutant (Cif-D129S), we then captured Cif in the substrate-bound, hydroxyalkyl-intermediate, and product-bound states for 1,2-epoxyhexane, yielding the first crystallographic snapshots of an EH at these key stages along the reaction coordinate. Taken together, our data illuminate the proposed two-step hydrolytic mechanism of a new class of bacterial virulence factor. They also suggest that the failure of WT Cif to accumulate a covalent hydroxyalkyl-enzyme intermediate reflects an active-site chemistry in which hydrolysis is no longer the rate-limiting step, a noncanonical kinetic regime that may explain similar observations with a number of other EHs.

The virulence factor cystic fibrosis transmembrane conductance regulator (CFTR) inhibitory factor (Cif) is secreted by Pseudomonas aeruginosa and is the founding member of a distinct class of epoxide hydrolases (EHs) that triggers the catalysis-dependent degradation of the CFTR. We describe here the development of a series of potent and selective Cif inhibitors by structure-based drug design. Initial screening revealed 1a (KB2115), a thyroid hormone analog, as a lead compound with low micromolar potency. Structural requirements for potency were systematically probed, and interactions between Cif and 1a were characterized by X-ray crystallography. On the basis of these data, new compounds were designed to yield additional hydrogen bonding with residues of the Cif active site. From this effort, three compounds were identified that are 10-fold more potent toward Cif than our first-generation inhibitors and have no detectable thyroid hormone-like activity. These inhibitors will be useful tools to study the pathological role of Cif and have the potential for clinical application.

Endocytic recycling of the cystic fibrosis transmembrane conductance regulator (CFTR) is blocked by the CFTR inhibitory factor (Cif). Originally discovered in Pseudomonas aeruginosa, Cif is a secreted epoxide hydrolase that is transcriptionally regulated by CifR, an epoxide-sensitive repressor. In this report, we investigate a homologous protein found in strains of the emerging nosocomial pathogens Acinetobacter nosocomialis and Acinetobacter baumannii ("aCif"). Like Cif, aCif is an epoxide hydrolase that carries an N-terminal secretion signal and can be purified from culture supernatants. When applied directly to polarized airway epithelial cells, mature aCif triggers a reduction in CFTR abundance at the apical membrane. Biochemical and crystallographic studies reveal a dimeric assembly with a stereochemically conserved active site, confirming our motif-based identification of candidate Cif-like pathogenic EH sequences. Furthermore, cif expression is transcriptionally repressed by a CifR homolog ("aCifR") and is induced in the presence of epoxides. Overall, this Acinetobacter protein recapitulates the essential attributes of the Pseudomonas Cif system and thus may facilitate airway colonization in nosocomial lung infections.

The Gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that secretes a multitude of virulence factors during the course of infection. Among these is Cif, an epoxide hydrolase (EH) that reduces the functional localization of the cystic fibrosis transmembrane conductance regulator in epithelial cells. In addition to being the first reported EH virulence factor, Cif possesses unique sequence deviations from canonical EH motifs. Foremost among these is the substitution of a histidine for the first epoxide ring-opening tyrosine in the active site. To test the functional equivalence of Tyr and His side chains at this position, we have generated the mutant Cif-H177Y. Structural analysis confirms that both the WT His and mutant Tyr side chains can be accommodated without large-scale conformational changes. However, the Tyr mutant is functionally inactive. Based on a detailed analysis of the structure of the Tyr mutant, it appears that Cif's main-chain conformation imposes a functional requirement for a His at this position. Comparison with canonical EH structures reveals additional conformational differences, which are coupled to divergent sequence characteristics. When used to probe the genomes of other opportunistic pathogens, these sequence-structure criteria uncover candidate sequences that appear to form a distinct subfamily of Cif-like epoxide hydrolases characterized by a conserved His/Tyr ring-opening pair.

The opportunistic pathogen Pseudomonas aeruginosa secretes a protein that triggers the accelerated degradation of the cystic fibrosis transmembrane conductance regulator (CFTR) in airway epithelial cells. This protein, which is known as the CFTR inhibitory factor (Cif), acts as a virulence factor and may facilitate airway colonization by P. aeruginosa. Based on sequence similarity Cif appears to be an epoxide hydrolase (EH), but it lacks several of the conserved features found in the active sites of canonical members of the EH family. Here, the crystallization of purified recombinant Cif by vapor diffusion is reported. The crystals formed in space group C2, with unit-cell parameters a = 167.4, b = 83.6, c = 88.3 A, beta = 100.6 degrees . The crystals diffracted to 2.39 A resolution on a rotating-anode source. Based on the calculated Matthews coefficient (2.2 A(3) Da(-1)), it appears that the asymmetric unit contains four molecules.

Cystic fibrosis transmembrane conductance regulator (CFTR) inhibitory factor (Cif) is a virulence factor secreted by Pseudomonas aeruginosa that reduces the quantity of CFTR in the apical membrane of human airway epithelial cells. Initial sequence analysis suggested that Cif is an epoxide hydrolase (EH), but its sequence violates two strictly conserved EH motifs and is also compatible with other alpha/beta hydrolase family members with diverse substrate specificities. To investigate the mechanistic basis of Cif activity, we have determined its structure at 1.8 A resolution by X-ray crystallography. The catalytic triad consists of residues Asp129, His297, and Glu153, which are conserved across the family of EHs. At other positions, sequence deviations from canonical EH active-site motifs are stereochemically conservative. Furthermore, detailed enzymatic analysis confirms that Cif catalyzes the hydrolysis of epoxide compounds, with specific activity against both epibromohydrin and cis-stilbene oxide, but with a relatively narrow range of substrate selectivity. Although closely related to two other classes of alpha/beta hydrolase in both sequence and structure, Cif does not exhibit activity as either a haloacetate dehalogenase or a haloalkane dehalogenase. Reassessment of the structural and functional consequences of the H269A mutation suggests that Cif's effect on host-cell CFTR expression may require hydrolysis of an extended endogenous epoxide substrate.