Signature Motifs Identify an Acinetobacter Cif Virulence Factor with Epoxide Hydrolase Activity

Christopher D Bahl,Kelli L Hvorecny,Andrew A Bridges,Alicia E Ballok,Jennifer M Bomberger,Kyle C Cady,George A O'Toole,Dean R Madden

doi:10.1074/jbc.m113.518092

Christopher D Bahl, Kelli L Hvorecny + Show 6 more

Open Access

https://doi.org/10.1074/jbc.m113.518092

Copy DOI

Abstract

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.

Highlights

Pathogens target airway clearance mechanisms to facilitate infection
We investigate a homologous protein found in strains of the emerging nosocomial pathogens Acinetobacter nosocomialis and Acinetobacter baumannii (“Acinetobacter Cif (aCif)”)
To begin our investigation of the aCif protein, we first performed a full sequence alignment with the CFTR inhibitory factor (Cif) protein from P. aeruginosa (Fig. 1). aCif contains a 24-residue N-terminal sequence predicted to act as a secretion signal by SignalP [45], corresponding to the validated signal sequence observed in Cif [33]

Summary

Introduction

Pathogens target airway clearance mechanisms to facilitate infection. Results: Sequence analysis reveals an Acinetobacter epoxide hydrolase (EH) that triggers loss of the cystic fibrosis transmembrane conductance regulator (CFTR). Like Cif, aCif is an epoxide hydrolase that carries an N-terminal secretion signal and can be purified from culture supernatants. These data confirm the ability of the Cif-specific motifs to identify EH proteins that inhibit CFTR abundance, and to flag a new potential class of virulence factors in opportunistic lung infections.

Results

Conclusion