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Investigators used genetically modified yeast
enzymes to pinpoint the mutations responsible for the antibiotic
resistance of Pneumocystis jirovecii, which causes a type of pneumonia
that is the most serious and prevalent AIDS-associated opportunistic
infection and a threat to other immunocompromised patients, such as
those undergoing therapy for cancer and organ transplantation.
Pneumonia was responsible for more than 61,000 deaths in the US in
2001, according to the National Center for Health Statistics.
Appearing in the January 23 Journal of Biological
Chemistry, the study examines the mutations responsible for disease's
tolerance toward atovaquone (ATV), a drug prescribed since 1995 that
inhibits a respiratory enzyme called the cytochrome bc1 complex, that
is essential for the pathogen's survival. The lead author, Dr. Jacques
Kessl, a research associate in biochemistry at DMS, said the study
addresses recent evidence that indicates that pathogens that cause
malaria and pneumonia are increasing resistance to ATV by developing
mutations that prevent the drug from acting on the bc1 complex.
"We were able to isolate the genetic mutations that
enable the pathogens to resist the drug when it is introduced to our
yeast samples," said Dr. Bernard Trumpower, professor of biochemistry
at DMS and corresponding author of the study. "As the genetically
modified yeast strains now display atovaquone resistance identical to
that found in pneumocystis, these yeast can be used to design new
drugs to make the appearance of resistance more unlikely."
The study builds on prior research in Trumpower's
lab that used yeast enzymes as accurate and easily modified models to
explore the resistance to ATV. It is not possible to grow pneumocystis
enzymes in the large quantities necessary to isolate and study the
cytochrome bc1 complex. Yeast is an excellent resource that can be
manufactured in large quantities and can be easily modified to take on
the qualities of more dangerous pathogens.
The researchers were able to genetically transfer
into the yeast cytochrome b mutations like those found in the
atovaquone resistant pneumocystis and found that these mutations
caused the yeast to acquire similar resistance to ATV. Additionally,
the team used a computer program to construct molecular models of the
enzymes. "We can now visualize the different mutations in three
dimensions to predict how the enzyme will react to different changes,
like the introduction of a new antibiotic," said co-author Benjamin
Lange, a research assistant at DMS.
"We are infinitely further along than we were three
years ago in terms of understanding the basis for resistance in these
organisms," said Trumpower. The co-authors of the study are Dr. Steven
Meshnick from the University of North Carolina and Dr. Brigitte
Meunier from the Wolfson Institute for Biomedical Research in London.
The study was funded in part by the NIH. |
