Worldwide, malaria accounts for 2-3 million deaths each year, including many children in Africa [67, 68]. In addition, 300 million clinical cases are estimated each year. Nearly half of the world’s population lives in regions where malaria is endemic. These facts have led the World Health Organization to issue a call for new drug development.
Malaria is transmitted by the
protozoan species Plasmodium. There
are four Plasmodium species that have
been identified to infect human being, P.
falciparum, P. vivax, P. ovalae and P. malariae. P. falciparum is the most lethal. We have established methodology that
has enabled others to pursue drug discovery in this field, and we have
assembled a panel of highly active enzymes from the four species of the malaria
parasite infecting humans [PfPM1, PfPM2, PfPM4, PvPM4, PoPM4, and PmPM4]. Because of our expanding catalog of cloned,
expressed and purified enzymes, which continues to grow, our combined
laboratories are in a unique position in the field of plasmepsin research. This
has resulted in several groups contacting us in past years to establish
collaborations to characterize new compounds as potential antimalarial drugs.
1. SCREENING FOR NATURAL OR SYNTHETIC COMPOUNDS THAT
COULD POTENTIALLY DEVELOP INTO HIGH-AFFINITY, HIGH-SPECIFICITY INHIBITORS. Long-term use of quinoline drugs promotes
the development of drug-resistant P. falciparum and P. vivax species. Novel anti-malarial drug targets are urgently needed to be discovered to battle these variants. Plasmepsins, a group of homologous aspartic proteinases, have been strongly considered as such potential targets. Our lab focuses on screening and designing specific and highly effective inhibitors against the potential drug targets, plasmepsins. The studies are carried out in both the kinetic and the structural level to help understand and improve the enzyme-inhibitor interactions. With the collaboration of several chemical synthesis labs world wide, such as Dr. Enrica Bosisio group, University of Milan, Italy, Dr. Anders Hallberg group, Uppsala University, Sweden, Dr. Stephan Quideau group, University Bordeaux 1, France, and Dr. Mark Hamann, University of Mississippi, USA., the inhibition effects of a variety of natural and synthesized compounds against plasmepsins can be tested in our lab. Compounds with high binding affinity are subjected to crystal growth trials in complex with related enzymes. In collaboration with our colleagues, Dr. Robert McKenna group, University of Florida, College of Medicine, high resolution X-ray crystal
structures can be resolved to allow analyzing enzyme-inhibitor interactions
and to guide us design more specific plasmepsin inhibitors. In collaboration
with our colleagues, Dr. John B. Dame group, University of Florida, College of Veterinary Medicine, and Dr. David Fidock, Albert Einstein College of Medicine, plasmepsin inhibitors can be tested
on the P. falciparum parasite culture to assess their antiparasitic effects.
Working on this project: Peng Liu –
graduate student
Chandan Kabadi – undergraduate student
Karan Desai – undergraduate student
Linda Janka – undergraduate student
Ben Blaweiss – undergraduate student
Andrew Sikes – undergraduate student
2. CHARACTERIZATION OF PLASMEPSINS
5, 9, 10. Upon the
completion of the P. falciparum genome project in 2002, it was discovered
through homology searches that the parasite’s genome encodes for ten aspartic
proteases, known as plasmepsins. Until
this discovery, our laboratory had only worked with the four plasmepsins
(plasmepsins 1, 2, 4, and HAP) found within the food vacuole of the parasite. Gene knockout studies of these four plasmepsins
have given preliminary data that suggest that these proteins may have a
redundant function within the parasite, leading us to search for new targets
within the parasite. Of the six
remaining putative plasmepsins, only three, plasmepsins 5, 9, and 10, are
expressed during the erythrocytic stage of infection. Our lab seeks to isolate and characterize these proteins using a
recombinant method of expression in order to find new drug therapies to help
patients infected with this disease.
A student working on this project will
learn how:
- To express,
refold, purify and optimize the conversion of the proenzyme to the mature
enzyme form of P. berghei plasmepsin 5 (PbPM5), or PbPM9 or PbPM10;
- To measure enzyme kinetic properties and inhibition by synthetic and
naturally occurring compounds;
Working on
this project: Melissa Marzahn – graduate student
3. CHARACTERIZATION OF ESSENTIAL PLASMEPSIN(S) OF THE
RODENT MALARIA PARASITE, PLASMODIUM BERGHEI,
AND THE BIRD MALARIA PARASITE P. GALLINACEUM in order to develop a convenient animal model
for pharmacokineticstudies of inhibitors.
Working on this project: Peng Liu – graduate student
Obehi Irumudomon – undergraduate
student
