Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A cGMP-dependent protein kinase (PKG) was recently identified as an anticoccidial target for the apicomplexan parasite Eimeria tenella [Gurnett, A., Liberator, P. A., Dulski, P., Salowe, S., Donald, R. G. K., Anderson, J., Wiltsie, J., Diaz, C., Harris, G., Chang, B., Darkin-Rattray, S. J., Nare, B., Crumley, T., Blum, P., Misura, A., Tamas, T., Sardana, M., Yuan, J., Biftu, T., and Schmatz, D. (2002) J. Biol. Chem. (in press)]. Unlike the PKGs of higher organisms that have two cGMP binding sites in their regulatory domain, the PKG from Eimeria tenella (Et-PKG) contains three putative cGMP binding sites and has distinctive activation properties, including a very large stimulation by cGMP ( approximately 1000-fold) with significant cooperativity (Hill coefficient of 1.7). During our investigation of Et-PKG activation, we found that 8-substituted cGMP analogues are weak partial activators. For example, 8-NBD-cGMP provides a maximal stimulation of activity of only 20-fold with little evident cooperativity, although cGMP can synergize with the analogue to provide full activation. The results suggest that partial activation is a consequence of restricted binding of 8-NBD-cGMP to a subset of cGMP sites in the enzyme. Site-directed mutagenesis of conserved arginine and glutamate residues in the parasite-specific third cGMP site confirms that this site is an important functional participant in the allosteric regulation of the kinase and that it exhibits very high selectivity against 8-NBD-cGMP. Since the results are consistent with full activation of Et-PKG requiring cyclic nucleotide binding in all three allosteric sites, one role for the additional cGMP site may be to establish a stricter regulatory mechanism for the kinase activity than is present in the PKGs of higher organisms containing only two allosteric sites.
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PMID:The role of a parasite-specific allosteric site in the distinctive activation behavior of Eimeria tenella cGMP-dependent protein kinase. 1191 85

Cyclic GMP-dependent protein kinase (PKG) has been biochemically and genetically validated in Toxoplasma gondii as a primary target responsible for the antiparasitic activity of the trisubstituted pyrrole 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1H pyrrol-3-yl] pyridine (Compound 1) [Biftu T, Feng D, Ponpipom M, et al. Synthesis and SAR of 2,3-diarylpyrrole inhibitors of parasite cGMP-dependent protein kinase as novel anticoccidial agents. Bioorg Med Chem Lett 2005;15:3296-301; Gurnett AM, Liberator PA, Dulski PM, et al. Purification and molecular characterization of cGMP-dependent protein kinase from Apicomplexan parasites. A novel chemotherapeutic target. J Biol Chem 2002;277:15913-22; Donald RGK, Allocco J, Singh SB, et al. Toxoplasma gondii cyclic GMP-dependent kinase: Chemotherapeutic targeting of an essential parasite protein kinase. Eukaryotic Cell 2002;1:317-28; Nare B, Allocco J, Liberator PA, Donald RGK. Evaluation of a cyclic GMP-dependent protein kinase inhibitor in treatment of murine Toxoplasmosis: Gamma interferon is required for efficacy. Antimicrob Agents Chemother 2002;46:300-7]. Compound 1 inhibits the growth of several related protozoan parasites of the subphylum Apicomplexa. Native PKG activity has been partially purified by cGMP-affinity and MonoQ ion exchange chromatography from Plasmodium falciparum (PfPKG). Biochemical fractions enriched for a 98kDa protein detected using anti-PKG antisera, contain cGMP-induced protein kinase activity that is sensitive to inhibition by Compound 1. To enable a more thorough characterization of PfPKG we expressed a synthetic cDNA incorporating T. gondii codon preference (Pf(Tg)PKG) in T. gondii parasites. The protein kinase activity of purified recombinant Pf(Tg)PKG is stimulated by cGMP, with significant cooperativity as demonstrated by a Hill coefficient of 2. Both substrate preference and inhibition of Pf(Tg)PKG kinase activity by Compound 1 are similar to that seen with native PfPKG, as well as PKG enzymes from Eimeria spp. and T. gondii. We conclude that PfPKG has biochemical and pharmacological properties that are similar to previously characterized apicomplexan PKG enzymes. Compound 1 is active against blood cell stages of P. falciparum cultured in vitro. In a Plasmodium berghei mouse model of infection, Compound 1 delays the onset of parasitemia but does not cure the parasite infection.
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PMID:Characterization of Plasmodium falciparum cGMP-dependent protein kinase (PfPKG): antiparasitic activity of a PKG inhibitor. 1632 79