Anticoccidial kinase inhibitors: Identification of protein kinase targets secondary to cGMP-dependent protein kinase

A novelToxoplasma gondiicalcium-dependent protein kinase

“…This invariant methionine residue was found also in PfCDPK2, PfCDPK4, but not in TgCDPK1. As decribed recently by Donald et al, 2006, TgCDPK4 would most likely be resistant to both classes of compound. The distribution of TgCDPK4 in extracellular and intracellular T. gondii parasites was analyzed using affinity purified anti-TgK4a and anti-Tg4b antibodies and compared to the anti-T. gondii-P30 surface protein (Fig.…”

“…On the contrary, the TgCDPK3 recently described by Donald et al, 2006 was insensitive to EGTA and not dependent on exogenous calcium. In P. falciparum, PfCDPK1 (Zhao et al, 1994) requires concentrations of calcium an order of magnitude higher than those required by the soybean enzyme.…”

“…2). In a recent publication, Donald et al (2002Donald et al ( , 2006 reported that TgCDPK1 and TgPKG (cGMP protein kinase) share a common sensitivity to pyrrole and imidazopyrimidine inhibitors due to a threonine residue in the catalytic binding pocket and substitution of this threonine residue with methionine prevented inhibitor binding. As TgCDPK3, the new TgCDPK4 also insert with an invariant methionine residue in the catalytic binding pocket 194 EKGHKRIHLVM 204 ELCTGKELYD 214 .…”

“…The predicted amino-acid sequence of TgCDPK4 shows similarity to CDPKs of plants and apicomplexan parasites. Among the 20 CDPK or CDPK-related kinases identified in T. gondii, only TgCDPK1 (Kieschnick et al, 2001) and TgCDPK3 proteins (Donald et al, 2006) were detected in tachyzoïtes. Because TgCDPK4 shares low identities with other TgCDPKs isoforms, we can assume that anti-TgCDPK4 antibodies are specific to TgCDPK4 and the cross reactivity with other TgCDPKs isoforms seems unlikely.…”

“…Indeed, TgCDPK1 was found to be inhibited by KT5926, a selective inhibitor of calmodulin-dependent and myosin light chain kinase, which is known to block the mobility of T. gondii (Dobrowolski et al, 1997). Recently another TgCDPK3 clone was isolated from the DNA library (Donald et al, 2006). In this study, we report the characterization of a new CDPK (TgCDPK4) from T. gondii.…”