microbiology ,

Molecule makes cells kill Chlamydia

DUKE (US) — A newly designed molecule disarms the pathogen responsible for the largest number of sexually transmitted infections in the United States.

The therapies that could come from this discovery mark a new type of antimicrobial approach. Instead of directly killing Chlamydia (Chlamydia trachomatis), the therapies disarm a central weapon of the bacterium and let the body take care of the rest.


Chlamydial infections are symptomless at the beginning, but can become chronic in women and lead to pelvic inflammatory disease and infertility as it infects cells in the uterus and fallopian tubes. It’s generally harmless to men. While these infections can be treated with antibiotics, infections can be easily reacquired and arise as a greater problem again. There are more than nearly 3 million new cases in the U.S. each year.

A virulence factor Chlamydia produces, called CPAF, emerged as a promising target to shut down because it plays an important role in protecting the bacteria within hiding places (vacuoles) in human cells. CPAF also prevents the human cell from committing suicide when it senses that it has been invaded by a pathogen (a common self-defense mechanism), giving the bacteria an extended chance to multiply and stay hidden.

Microbiologists and genetics experts led by Raphael Valdivia, an associate professor in the molecular genetics and microbiology department at Duke University, completed the work that narrowed down the search to an enzyme that Chlamydia produces, a protease called CPAF. The work was featured on the cover of the journal Cell Host and Microbe.

“Chlamydia makes this master protease that takes over the whole cell and prevents it from mounting an effective, pathogen-killing immune response,” says Valdivia. “Chlamydia is unique among pathogens, in that it can co-exist within humans without causing symptoms for a long time. This reflects a careful balance between the host and the pathogen.

“We think CPAF is central to this balance. Therefore, if we disarm it, we can tilt the equation toward the human host and mount an effective immune response that will not only clear the infection but prevent it from re-emerging.”

The Duke chemists, led by Dewey McCafferty, a professor in the chemistry and biochemistry departments, designed a molecule that could block the CPAF activity inside of human cells.

“Typically, to design a potent, specific, and cell-permeable inhibitor is a complicated undertaking and inhibitor designs don’t work right away,” McCafferty says. “But in this case, it worked on the first try. Professor Valdivia’s group of microbiologists and my group of chemical biologists worked to establish which qualities we needed to incorporate into a CPAF inhibitor.

“The results are very exciting, because we have an inhibitor lead molecule that may form the basis for a new class of anti-Chlamydial drugs.”

They found that when CPAF was blocked over time by their designed molecule, the protective home that the bacteria make for themselves within the infected cells degraded, and CPAF no longer could degrade the proteins in the cell that would normally mount an immune response to the infection.

When CPAF is inhibited, the infected human cells effectively “commit suicide,” Valdivia says. “When the infected human cell dies, so does Chlamydia, and this ends the infection.”

Valdivia says the findings could yield new therapeutic approaches that might turn a natural infection into a vaccination.

“By stopping the cloaking response of the bacteria, we are essentially revealing where they are in the cell and allowing our own immune system to take over and destroy the pathogens,” McCafferty says.

Researchers from Duke and the University of North Carolina at Chapel Hill collaborated on the work, which was supported by the National Institutes of Health, the Burroughs Wellcome Fund, the Crohn’s and Colitis Foundation of America, and a CR Hauser Fellowship.

More news from Duke University: http://today.duke.edu/

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