Chlamydia trachomatis responds to heat shock, penicillin induced persistence, and IFN-gamma persistence by altering levels of the extracytoplasmic stress response protease HtrA

Wilhelmina M Huston,Peter Timms,Christina Theodoropoulos,Sarah A Mathews

doi:10.1186/1471-2180-8-190

Abstract

BackgroundChlamydia trachomatis, an obligate intracellular human pathogen, is the most prevalent bacterial sexually transmitted infection worldwide and a leading cause of preventable blindness. HtrA is a virulence and stress response periplasmic serine protease and molecular chaperone found in many bacteria. Recombinant purified C. trachomatis HtrA has been previously shown to have both activities. This investigation examined the physiological role of Chlamydia trachomatis HtrA.ResultsThe Chlamydia trachomatis htrA gene complemented the lethal high temperature phenotype of Escherichia coli htrA- (>42°C). HtrA levels were detected to increase by western blot and immunofluorescence during Chlamydia heat shock experiments. Confocal laser scanning microscopy revealed a likely periplasmic localisation of HtrA. During penicillin induced persistence of Chlamydia trachomatis, HtrA levels (as a ratio of LPS) were initially less than control acute cultures (20 h post infection) but increased to more than acute cultures at 44 h post infection. This was unlike IFN-γ persistence where lower levels of HtrA were observed, suggesting Chlamydia trachomatis IFN-γ persistence does not involve a broad stress response.ConclusionThe heterologous heat shock protection for Escherichia coli, and increased HtrA during cell wall disruption via penicillin and heat shock, indicates an important role for HtrA during high protein stress conditions for Chlamydia trachomatis.

Highlights

Chlamydia trachomatis, an obligate intracellular human pathogen, is the most prevalent bacterial sexually transmitted infection worldwide and a leading cause of preventable blindness
HtrA is highly conserved between Chlamydia species and is homologous to E. coli HtrA There is considerable knowledge of the key residues and domains involved in the protease and chaperone activities for HtrA from E. coli (EcHtrA), and high conservation of these residues in other bacterial HtrA homologs has been reported [20,21,22]
PDZ1 sequence is highly conserved between chlamydial HtrAs, functions in E. coli HtrA for coordinating substrate binding and access to the active site, including by binding of the carboxyl terminal of the protein substrates, PDZ2 is known to function in protein interaction within the E. coli HtrA hexameric structure [23,24]

Summary

Introduction

An obligate intracellular human pathogen, is the most prevalent bacterial sexually transmitted infection worldwide and a leading cause of preventable blindness. HtrA is a virulence and stress response periplasmic serine protease and molecular chaperone found in many bacteria. Recombinant purified C. trachomatis HtrA has been previously shown to have both activities. This investigation examined the physiological role of Chlamydia trachomatis HtrA. HtrA has since been reported to be a periplasmic protease and chaperone during E. coli extracytoplasmic stress response, with a structural temperature switch to mediate between these two activities [4,5,6]. We characterised purified recombinant HtrA from Chlamydia (C.) trachomatis L2, demonstrating that it had biochemical features typical of a HtrA protease, and critically, that it was capable of both protease and chaperone activities at physiologically relevant temperatures [8]. The physiological function of HtrA during the developmental cycle of Chlamydia is currently unknown

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