title: Characterization of Plasmodium falciparum protein kinase 2.
abstract: A sustained elevation of free Ca(2+) is observed on the rupture and release of merozoites of Plasmodium falciparum from the erythrocytes. The immunoelectron micrographs demonstrate that calmodulin is localized in merozoites. To elucidate the Ca(2+) signal of P. falciparum invasion, we attempted to characterize P. falciparum protein kinase 2 (PfPK2), which is homologous to human calcium calmodulin-dependent protein kinase (CaMK). PfPK2 was purified as a fusion protein that was labeled with [gamma-(32)P]ATP; this labeling was then eliminated by phosphatase. This phosphorylation was eliminated when the putative catalytic lysine residue of PfPK2 was replaced with alanine. PfPK2 phosphorylated histone II(AS) as a representative substrate in a Ca(2+)- and calmodulin-dependent manner. Calmodulin antagonists inhibited the phosphorylation of PfPK2 in vitro and markedly decreased the parasitemia of ring forms in an invasion assay, whereas CaMKII-specific inhibitors had no effect. PfPK2 was localized in the merozoites in the culture of P. falciparum. Thus, purified PfPK2 possesses protein kinase activity in a Ca(2+)- and calmodulin-dependent manner and the catalytic lysine of this protein was determined. These data suggest that PfPK2 is the Plasmodium protein kinase expressed in the merozoites during the invasion stage.
authors.affiliation: Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan. akkato@mail.ecc.u-tokyo.ac.jp
authors.forename: Kentaro
authors.initials: K
authors.lastname: Kato
authors.forename: Atsushi
authors.initials: A
authors.lastname: Sudo
authors.forename: Kyousuke
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Yukinobu
authors.initials: Y
authors.lastname: Tohya
authors.forename: Hiroomi
authors.initials: H
authors.lastname: Akashi