A Plant-Like Kinase in Plasmodium falciparum Regulates Parasite Egress from Erythrocytes

Abstract

Clinical malaria is associated with the proliferation of Plasmodium parasites in human erythrocytes. The coordinated processes of parasite egress from and invasion into erythrocytes are rapid and tightly regulated. Here we found that the plant-like calcium-dependent protein kinase PfCDPK5, which is expressed in invasive merozoite forms of Plasmodium falciparum, was critical for egress. Parasites deficient in PfCDPK5 arrested as mature schizonts with intact membranes, despite normal maturation of egress proteases and invasion ligands. Merozoites physically released from stalled schizonts were capable of invading new erythrocytes, separating the pathways of egress and invasion. The arrest was downstream of cGMP-dependent protein kinase (PfPKG) function and independent of protease processing. Thus PfCDPK5 plays an essential role of PfCDPK5 during the blood-stage of malaria replication.

An evolutionary perspective on the kinome of malaria parasites

“…This approach culminated in a kinome-wide study demonstrating that 23 P. berghei ePKs are redundant for asexual erythrocytic parasite development in mice and identifying phenotypes in sexual development for a number of these 23 ePKs [51]. A similar strategy in P. falciparum identified roles for an orphan kinase in proliferation rate linked to the number of progeny merozoites per schizont [36], for an eIF2a kinase in response to starvation stress, similar to GCN2, its closest homologue in yeast [52], and for CDPKs in motility during invasion [53] or egress of merozoites from the erythrocyte [54], to cite a few specific studies; more recently, a kinome-wide approach [19] identified 36 ePKs as refractory to gene disruption, and thus as likely crucial players in asexual proliferation in erythrocytes.…”

“…Many of these phosphorylations were on sites within their activation loops and therefore potentially associated with the regulation of catalytic activity [66]. These include, in addition to PfGSK3 and PfCLK3 already discussed, activation loop phosphorylation of the cyclic nucleotide-dependent kinases PfPKA (PFI1685w) and PfPKG (PF14_0346) [19], both of which have crucial functions in the erythrocytic cycle [54,[67][68][69][70]. How are these kinases regulated?…”

Does protein phosphorylation govern host cell entry and egress by the Apicomplexa?

“…Parasites treated only in the schizont stage became dysmorphic, were unable to rupture, and the merozoites released were not invasive (Taylor et al, 2010). Others have found that schizont treatment with compound 1 inhibited processing of the major surface protein 1 (PfMSP1) by the protease subtilisin 1 (PfSUB1), indicating that PKG acts upstream of the protease cascade (Dvorin et al, 2010). Egress of Plasmodium relies on protease activity in order to escape from the PVM (Blackman, 2008).…”

“…Egress of Plasmodium relies on protease activity in order to escape from the PVM (Blackman, 2008). PfCDPK5, a membraneassociated kinase expressed in late schizonts and merozoites was recently demonstrated to act downstream of this protease cascade (Dvorin et al, 2010). PfCDPK5-deficient parasites were arrested in mature schizonts with no apparent ultrastructure defects, and the processing of PfMSP1 by PfSUB1 was unaffected.…”

“…Mechanically egressed PfCDPK5-deficient merozoites retained their ability to invade, excluding a block in microneme secretion. The authors therefore proposed a model of parasite egress where the protease cascade is necessary but not sufficient and where the final stages of the rupture of the PVM and the erythrocyte plasma membrane are downstream of PfCDPK5 (Dvorin et al, 2010).…”