Malaria is the most common and deadly parasitic disease in the world. A number of factors have contributed to making malaria as serious a problem now as it was during the first half of the twentieth century. In any given year, there will be 300-500 million cases of malaria and 1-3% of those who contract the disease will not survive. Over 90% of the cases and deaths occur in Africa.  As bad as that is, some experts foresee as much as a 20% annual increase in Africa's rate of malaria-related illness and death.  Each year the world over, malaria destroys, through premature death and disability, the equivalent of at least 35 million years of healthy, productive human life and to date, there is no effective subunit vaccine for malaria. The incidence of drug-resistant parasite is increasing worldwide. The sequencing of the Plasmodium falciparum (and Plasmodium yoelii), the Anopheles gambiae and the Homo sapiens (and Mus musculus) genomes, the three organisms that comprise the complex life cycle of the malaria parasite, is complete and will aid in the study of the complex interactions responsible for the disease. Our laboratory is undertaking the investigation of two diverse topics, the protein-protein interactions involved in the invasion pathway and the whole genome expression analysis of various stages of the parasite life cycle, to potentially identify new targets for immunologic or chemotherapeutic intervention.

The invasive stages of apicomplexan parasites actively penetrate host cells, an essential ability for maintaining an intracellular lifestyle. What has become clear is that numerous parasite and host cell components participate in the rapid invasion process. Of the numerous blood-stage malaria antigens that have been identified in both infected humans and in animal models of this disease, the clearest rationale for a blood-stage vaccine candidate exists for the merozoite surface protein-1 (MSP-1). MSP-1 is synthesized as a large (approximately 200 kDa) precursor during schizogony and is processed after merozoite egress from the erythrocyte into a series of proteolytic fragments but remains associated with the merozoite, with a uniform distribution on the surface of the parasite. Despite the studies available on the MSP-1 protein, we have little definitive information on its role or roles in the functioning of Plasmodium species. We have utilized the yeast two-hybrid system to examine the protein-protein interactions involving P. yoelii MSP-1 and have identified both intramolecular and intermolecular interactions involving regions of the MSP-1 molecule. Ongoing studies are investigating the biological role of these critical interactions. The process of parasite invasion also involves a unique actin-myosin based motor that is localized between the plasma membrane and the inner membrane complex, a structure formed by two closely aligned membranes and supported by microtubules. Transmembrane proteins displaying adhesive properties were predicted to link the extracellular substrates with the motor. Again, using the yeast two-hybrid system and a bioinformatic approach we have identified components that link the actin-myosin motor to the inner membrane complex and may form one of the junctions involved in linking the parasite to the RBC to be invaded. Ongoing studies are identifying the key interactions with these molecules in the invasion process.

The second major aspect of the work in the laboratory involves the use of long-oligonucleotide gene-specific microarray to examine global patterns of gene expression in various stages of the rodent malaria P. yoelii. Primarily, in collaboration with Dr. Stefan Kappe of the Seattle Biomedical Research Institute, we are examining the pattern of parasite gene expression in the infected liver of a mouse subsequent to infection with salivary gland sporozoites, isolated from a mosquito. The large number of differentially expressed genes detected in this analysis suggests that extensive transcriptional regulation has a major role in the functional specialization of parasite development. Further characterization of the numerous liver-specific products in now underway.