Development of transgenic Plasmodium falciparum parasites for K+ channel functional investigation

Abstract

The elimination of the life-threatening malaria disease caused by Plasmodium falciparum parasites remains a global health challenge. It is imperative that novel biological targets are identified not only in the pathogenic asexual parasites, but also in the transmissible sexual gametocytes. However, the development of transmission-blocking interventions is difficult, as the biology behind important physiological processes during gametocyte development is not well understood. One such process is ion homeostasis, which is critical for P. falciparum parasites to maintain through the combined action of various ion transport pathways. A chemically diverse array of antiplasmodial compounds has been identified to disrupt ion homeostasis in P. falciparum parasites by disrupting the Na+ gradient that is maintained by a cation ATPase, PfATP4. Similarly, interference of the K+ gradient by ionophores, such as salinomycin, inhibits the proliferation of asexual parasites and the differentiation of gametocytes of parasites of P. falciparum. Two putative K+ channels (PfK1 and PfK2) could be involved in maintaining the K+ gradient in P. falciparum parasites. Of these, only PfK2 is expressed throughout gametocytogenesis, indicating that it is solely responsible for maintaining the K+ gradient during these developmental stages. Since interference of the K+ gradient prevents the development of gametocytes, PfK2 is believed to be associated with important biological processes during these stages. This study aimed to generate transgenic P. falciparum pfk2 parasites for genetic disruption as well as conditional knockdown studies.

Pfk2 was targeted for genetic disruption to generate a truncated version of the protein. A 5’ gene fragment was successfully cloned into a specialized gene disruption plasmid (pSLI-TGD), which included a selection-linked integration technique to select for genomic integration. Recombinant plasmids were transfected into asexual parasites twice, but for both attempts, parasites never recovered after drug pressure for episomal uptake. For the conditional knockdown approach, transgenic parasite lines were successfully generated, in which pfk2 was modified with a glmS ribozyme to regulate the level of mRNA and ultimately the amount of gene product synthesized. Furthermore, pfk2 was tagged with a green fluorescent protein for localization studies. This study has provided genetically modified parasites that will allow for future investigation of the functional relevance of PfK2 for P. falciparum parasites through a conditional knockdown system.