Toxoplasma gondiiAttachment to Host Cells Is Regulated by a Calmodulin-like Domain Protein Kinase
The role of calcium-dependent protein kinases in the invasion ofToxoplasma gondiiinto its animal host cells was analyzed. KT5926, an inhibitor of calcium-dependent protein kinases in other systems, is known to block the motility ofToxoplasmatachyzoites and their attachment to host cells.In vivo, KT5926 blocks the phosphorylation of only three parasite proteins, and in parasite extracts only a single KT5926-sensitive protein kinase activity was detected. This activity was calcium-dependent but did not require calmodulin. In a search for calcium-dependent protein kinases inToxoplasma, two members of the class of calmodulin-like domain protein kinases (CDPKs) were detected. TgCDPK2 was only expressed at the mRNA level in tachyzoites, but no protein was detected. TgCDPK1 protein was expressed inToxoplasmatachyzoites and cofractionated precisely with the peak of KT5926-sensitive protein kinase activity. TgCDPK1 kinase activity was calcium-dependent but did not require calmodulin or phospholipids. TgCDPK1 was found to be inhibited effectively by KT5926 at concentrations that block parasite attachment to host cells.In vitro, TgCDPK1 phosphorylated three parasite proteins that migrated identical to the three KT5926-sensitive phosphoproteins detectedin vivo. Based on these observations, a central role is suggested for TgCDPK1 in regulatingToxoplasmamotility and host cell invasion.