Molecular mechanisms of the malaria parasite
Malaria is one of the most ancient unresolved afflictions of humankind. This disease is caused by the Plasmodium parasite, of which Plasmodium falciparum is the deadliest species. Malaria continues to affect upwards of half a billion people worldwide and kills over 1.5 million persons annually, mostly young children in sub-Saharan Africa. While there have been major global efforts to eliminate this disease, including eradication of the mosquito vector as well as developing chemotherapeutics against the blood-stage parasite, this disease continues to present a major health burden in afflicted regions. A major concern is the rapid evolution of drug-resistant strains worldwide and the lack of new chemotherapeutics. The challenge we face is to identify and characterize novel drug targets for anti-malarial strategies.
The lifecycle of Plasmodium is highly complex and involves three major stages of development: 1) a mosquito stage, 2) a liver stage and 3) a red blood cell stage. During the repetitive 48-hour red blood cell stage, the parasite undergoes an incredibly diverse set of morphologically distinct developmental transitions, from red blood cell invasion to rupture and reinvasion. This cycle of infection and persistence in the red blood cells is responsible for the severe clinical outcome of the malaria disease.Many of the fundamental aspects of this parasite and its relationship with the human host are not clearly understood. One of the main questions is understanding how the parasite controls its developmental progression within the red blood cell. What are the factors that it uses to control this development? How does it interact with and sense the extracellular environment? And how are alternative developmental programs realized by the parasite?
We are using a combination of genomics, biochemistry, and bioinformatics to address these issues with the goal of devising ways to disrupt the parasite lifecycle.
Transcriptional regulation in Plasmodium falciparum
The whole genome sequence of Plasmodium falciparum has recently been completed, revealing several unique features. This landmark has opened up exciting possibilities for novel approaches toward research in malaria and has led to an increased fervor to identify new potential targets for anti-malarial drugs and vaccines. Surprisingly, approximately 60% of the predicted open reading frames share no homology to those of any other known organism. In addition, the genomic nucleotide composition is over 80% A/T in coding regions and 90% in non-coding regions. Lastly, there is a paucity of regulatory transcription factors in comparison to other eukaryotic organisms. This suggests that regulation of gene expression throughout development may be governed by a small number of factors or by a novel mechanism. In support of this hypothesis, the global transcriptional program of the intraerythrocytic developmental cycle (IDC) exhibits a continuous cascade of gene expression.
My lab is applying a variety of whole-genome approaches to investigate the molecular mechanism of transcriptional regulation in P. falciparum. Using DNA microarrays to analyze changes in transcription due to environmental perturbations such as drug challenge, we hope to define specific pathways which are triggered by these stimuli. We will also apply a variety of biochemical approaches to identify the factors involved in these regulatory processes. Further mutational analysis and knockouts of these factors coupled with structural analyses will help to unravel the details of gene regulation and the effects on genome wide transcription in vivo. We would also like to understand the interaction between these factors and the parasite genome. By using chromatin immunoprecipitation (ChIP-chip) methods, we plan to identify the cognate recognition sequences used by these putative regulatory proteins as well as their genome-wide distribution.
Plasmodium falciparum genome exploration
Although over half of the predicted P. falciparum genes have no known homologue in any other species, we have found that most of these novel genes are expressed, and thus presumably utilized, throughout the blood stage developmental cycle. While occasionally these unknown genes have homology to other P. falciparum sequences, often this is not the case. We can exploit the IDC transcriptome data to identify gene subgroups with similar expression profiles and potentially similar functions. In addition, we are now developing computational tools to analyze these novel or “hypothetical” protein sequences more rigorously incorporating all available sequence information from other Plasmodium species. This comparative analysis between genomes not only detects inter-species variability, but also identifies essential portions of the genome through well-conserved regions. Lastly, we are interested in the large portion of the P. falciparum genome that is comprised of genes rich in repetitive sequences. It is well established that these repeats vary from strain to strain and are especially common to antigens involved in host immune evasion. However, it remains to be determined whether these repeats encode regions of flexibility, interaction domains for other proteins, or simply share common structural motifs.