Using Click Chemistry to Identify Potential Drug Targets in Plasmodium
Technical Report,30 Sep 2013,29 Mar 2016
Rutgers, The State University of New Jersey Newark United States
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Sporozoite infection of the liver is the first obligate step of the Plasmodium mammalian cycle. Identifying parasite proteins that are required for liver infection can lead to novel drugs against malaria. For the first time, we report an essential role for two signaling pathways in sporozoite infectivity - cGMP signaling, mediated through the parasites cGMP-dependent protein kinase PKG, and Ca2 signaling, mediated through the parasites calcium-dependent protein kinase 4 CDPK4. We demonstrated that both enzymes are expressed cytoplasmically in sporozoites and liver stages. Using a specific and potent inhibitor of Plasmodium PKG and inhibitor-resistant transgenic parasites, we demonstrated that PKG is essential for sporozoite invasion and consequently infection of hepatocytes. In addition to PKG, CDPK4 is crucial for sporozoite invasion. We showed that inhibiting CDPK4 activity in sporozoites, using either a small molecule inhibitor or conditional deletion of the gene, significantly decreases invasion and infection of hepatocytes. Simultaneous chemical inhibition of PKG and CDPK4 resulted in a cooperative block in sporozoite infection. In conclusion, we have identified two protein kinase signaling pathways that play a key role in sporozoite infection and whose inhibition could be exploited to prevent the first step of a malaria infection. Thus, we have identified two potential targets for development of drugs that restrict liver infection by Plasmodium.