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CPAF: a Chlamydial protease in search of an authentic substrate
Allan L Chen1, Kirsten A Johnson, Jennifer K Lee
1Department of Microbiology and Molecular Genetics, University of California at Irvine, Irvine, California, USA.
Abstract:
Bacteria in the genus Chlamydia are major human pathogens that cause an intracellular infection. A chlamydial protease, CPAF, has been proposed as an important virulence factor that cleaves or degrades at least 16 host proteins, thereby altering multiple cellular processes. We examined 11 published CPAF substrates and found that there was no detectable proteolysis when CPAF activity was inhibited during cell processing. We show that the reported proteolysis of these putative CPAF substrates was due to enzymatic activity in cell lysates rather than in intact cells. Nevertheless, Chlamydia-infected cells displayed Chlamydia-host interactions, such as Golgi reorganization, apoptosis resistance, and host cytoskeletal remodeling, that have been attributed to CPAF-dependent proteolysis of host proteins. Our findings suggest that other mechanisms may be responsible for these Chlamydia-host interactions, and raise concerns about all published CPAF substrates and the proposed roles of CPAF in chlamydial pathogenesis.
Insights
Chlamydia protease CPAF
Area of Science:
- Microbiology
- Cell Biology
- Pathogenesis
Background:
- Chlamydia are intracellular bacterial pathogens.
- Chlamydial protease CPAF is a proposed virulence factor.
- CPAF is thought to degrade host proteins to alter cellular processes.
Purpose of the Study:
- To investigate the role of CPAF in host protein degradation.
- To determine if CPAF-mediated proteolysis occurs in intact infected cells or in cell lysates.
- To re-evaluate the proposed functions of CPAF in Chlamydia pathogenesis.
Main Methods:
- Analysis of 11 previously identified CPAF substrates.
- Inhibition of CPAF activity during cell processing.
- Comparison of proteolysis in intact cells versus cell lysates.
Main Results:
- No detectable proteolysis of 11 putative CPAF substrates was observed when CPAF activity was inhibited.
- Reported proteolysis of these substrates occurred due to enzymatic activity in cell lysates, not in intact Chlamydia-infected cells.
- Chlamydia-induced host cell alterations, such as Golgi reorganization and apoptosis resistance, were observed despite the lack of direct CPAF proteolysis.
Conclusions:
- The previously reported CPAF substrates are likely not degraded by CPAF in intact infected cells.
- Other mechanisms, not CPAF-dependent proteolysis, may mediate Chlamydia-induced host cell interactions.
- The proposed roles of CPAF in chlamydial pathogenesis and the validity of published CPAF substrates require re-examination.
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