A TENTH of the malaria parasite鈥檚 genes turn out to be plant genes. That means drugs based on weedkillers could be used to treat the disease, which kills more than a million people a year.
鈥淭here are 500 proteins that are plant proteins that humans don鈥檛 have. Drugs that target those proteins probably won鈥檛 have side effects on us,鈥� says botanist Geoff McFadden of the University of Melbourne.
The sequence of the parasite鈥檚 genome, and that of its host the Anopheles mosquito, were published in Nature and Science last week. One of the discoveries, which surprised many experts, was that roughly 550 of malaria鈥檚 5300 genes code for proteins that are found in an organelle within the parasite called the apicoplast.
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Apicoplasts were discovered only six years ago and are very similar to chloroplasts, the organelles in plant cells that contain the photosynthetic machinery. But the malaria parasite is an animal. So the theory is that the parasite evolved from an organism that engulfed an algal cell hundreds of millions of years ago, and retained the chloroplasts of the algae. 鈥淚t鈥檚 a product of PacMan evolution,鈥� Neil Hall of the Wellcome Trust Sanger Institute told a press conference in London Last week.
Apicoplasts no longer carry out photosynthesis, but are still vital chemical factories for the malaria parasite. They make fatty acids, which the parasite needs to enable it to invade blood cells, as well as chemicals that produce energy.
McFadden鈥檚 team, which helped discover apicoplasts and took part in the genome sequencing effort, has already shown that one herbicide, diclofop, kills parasites in a test tube. And another team has cured mice of malaria with a herbicide called fosmidomycin. German biotech company Jomaa Pharmaka of Giessen is now trying to develop a drug based on fosmidomycin.
Sequencing the parasite is revealing even more ways to kill the malaria parasite. 鈥淲e鈥檝e got at least 10 new drug targets in the apicoplast from the genome sequence, and we expect lots more,鈥� says botanist Stuart Ralph, who works with McFadden.
That鈥檚 crucial because malaria rapidly becomes resistant to drugs, so new ones need to be introduced when old ones start to fail. 鈥淗aving a large number of drug targets helps a lot in getting a large number of drugs quickly,鈥� says Alan Cowman, a malaria expert at the Walter and Eliza Hall Institute in Melbourne. Neil Hall, speaking in London, said that Triclosan, the antimicrobial agent added to mouthwashes and other toiletries also showed promise against the apicoplast in the lab.
The apicoplasts may explain another mystery: why some antibiotics designed to kill bacteria also kill the malaria parasite. Chloroplasts, and hence apicoplasts, are themselves derived from photosynthetic bacteria.
