Researchers at the Virginia Bioinformatics Institute (VBI) at Virginia Tech have identified Heme Detoxification Protein (HDP), a unique protein encoded in the malaria genome that represents a potential target for developing new malaria drugs. The team has also demonstrated that HDP plays a major role in protecting Plasmodium as the pathogen pursues infection of its host. The findings were published April 25th in the open-access journal PLoS Pathogens.

Worldwide, the annual death toll of malaria exceeds 1 million, and children under the age of five are its major victims. The Plasmodium parasite that causes malaria in humans is transmitted through the bites of infected mosquitoes. Once inside the human body, the parasite initially develops in the liver and subsequently, upon release, infects red blood cells.

After infecting host red blood cells, a rapid growth ensues, supported by the parasite's consumption of hemoglobin, the oxygen-transporting protein that constitutes a massive 90% of the total protein present inside each red blood cell. Destruction on this scale releases large quantities of heme, the prosthetic group responsible for oxygen transport in hemoglobin. Free heme is extremely damaging and to protect itself from this toxic onslaught, the parasite utilizes a novel mechanism where it rapidly converts heme into a crystalline material known as hemozoin.

Dr. Dharmendar Rathore, leader of the team that also included researchers at Washington University School of Medicine, the US National Institutes of Health, and the US Food and Drug Administration, said: "We discovered HDP as part of a functional genomics initiative that is focused on the identification of malaria proteins involved in disease pathology. It appears that HDP has a number of striking features that make it a promising candidate as a drug target. HDP is not only capable of rapidly converting heme into its non-toxic counterpart hemozoin, but it is highly conserved in all the species of the parasite and also appears to be critical for its survival. The beauty of this discovery is that, while HDP has robust interactions with heme, it lacks homology to any of the known heme-binding proteins and has therefore eluded detection during previous attempts by several groups to identify parasite factors responsible for hemozoin formation."

The conversion of heme into hemozoin is regarded as one of the weakest links in the life cycle of the Plasmodium parasite. For example, chloroquine, the most widely used malaria drug, works by interacting with heme and preventing its detoxification into hemozoin. However, drugs are not yet available that target any of the parasite-specific molecules involved in this process.

Dr. Rana Nagarkatti, a co-author, said: "The identification of new drug targets is an essential step in the development of next-generation drugs for treating malaria. Drugs that specifically interact with HDP and inhibit its detoxification activities could potentially have drastic effects on the viability of the malaria parasite."

Dr. Rathore added: "We have recently undertaken a high-throughput screening of chemical libraries to identify compounds that can inhibit the activity of HDP. Several lead compounds were identified and have been characterized in our laboratory at VBI and subsequently validated at the Swiss Tropical Institute in Basel, Switzerland. We see considerable potential in developing these lead compounds into new drugs that can act by blocking the function of HDP in the parasite."

HDP - A Novel Heme Detoxification Protein from the Malaria Parasite
Jani D, Nagarkatti R, Beatty W, Angel R, Slebodnick C, et al. (2008)
PLoS Pathog 4(4): e1000053. doi:10.1371/journal.ppat.1000053
Click here to view article online.

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