Mechanism of allosteric inhibition in thePlasmodium falciparumcGMP-dependent protein kinase

Most malaria deaths are caused by the protozoan parasitePlasmodium falciparum. Its life cycle is regulated by a cGMP-dependent protein kinase (PfPKG), whose inhibition is a promising antimalaria strategy. Allosteric kinase inhibitors, such as cGMP analogs, offer enhanced selectivity relative to competitive kinase inhibitors. However, the mechanisms underlying allostericPfPKG inhibition are incompletely understood. Here, we show that 8-NBD-cGMP is an effectivePfPKG antagonist. Using comparative NMR analyses of a key regulatory domain,PfD, in itsapo, cGMP-bound, and cGMP analog?bound states, we elucidated its inhibition mechanism of action. Using NMR chemical shift analyses, molecular dynamics simulations, and site-directed mutagenesis, we show that 8-NBD-cGMP inhibitsPfPKG not simply by reverting a two-state activeversusinactive equilibrium, but by sampling also a distinct inactive ?mixed? intermediate. Surface plasmon resonance indicates that the ability to stabilize a mixed intermediate provides a means to effectively inhibitPfPKG, without losing affinity for the cGMP analog. Our proposed model may facilitate the rational design ofPfPKG-selective inhibitors for improved management of malaria.