Browsing AHU Faculty Scholarship by Author "Adams, John H."
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- ItemAtypical Mitogen-activated Protein Kinase Phosphatase Implicated in Regulating Transition from Pre-S-Phase Asexual Intraerythrocytic Development of Plasmodium falciparum(Eukaryotic Cell, 2013) Balu, Bharath; Campbell, Christopher; Sedillo, Jennifer; Maher, Steven; Singh, Naresh; Thomas, Phaedra; Zhang, Min; Pance, Alena; Otto, Thomas D.; Rayner, Julian C.; Adams, John H.Intraerythrocytic development of the human malaria parasite Plasmodium falciparum appears as a continuous flow through growth and proliferation. To develop a greater understanding of the critical regulatory events, we utilized piggyBac insertional mutagenesis to randomly disrupt genes. Screening a collection of piggyBac mutants for slow growth, we isolated the attenuated parasite C9, which carried a single insertion disrupting the open reading frame (ORF) of PF3D7_1305500. This gene encodes a protein structurally similar to a mitogen-activated protein kinase (MAPK) phosphatase, except for two notable characteristics that alter the signature motif of the dual-specificity phosphatase domain, suggesting that it may be a low-activity phosphatase or pseudophosphatase. C9 parasites demonstrated a significantly lower growth rate with delayed entry into the S/M phase of the cell cycle, which follows the stage of maximum PF3D7_1305500 expression in intact parasites. Genetic complementation with the full-length PF3D7_1305500 rescued the wild-type phenotype of C9, validating the importance of the putative protein phosphatase PF3D7_1305500 as a regulator of pre-S-phase cell cycle progression in P. falciparum.
- ItemIn Silico Characterization of an Atypical MAPK Phosphatase of Plasmodium Falciparum as a Suitable Target for Drug Discovery(Chemical Biology and Drug Design, 2014) Campbell, Christopher; Santiago, Daniel N.; Guida, Wayne C.; Manetsch, Roman; Adams, John H.Plasmodium falciparum , the causative agent of malaria, contributes to significant morbidity and mortality worldwide. Forward genetic analysis of the blood-stage asexual cycle identified the putative phosphatase from PF3D7_1305500 as an important element of intraerythrocytic development expressed throughout the life cycle. Our preliminary evaluation identified it as an atypical MAPK phosphatase. Additional bioinformatics analysis delineated a conserved signature motif and three residues with potential importance to functional activity of the atypical dual-specificity phosphatase (DUSP) domain. A homology model of the DUSP domain was developed for use in high-throughput in silico screening of the available library of antimalarial compounds from ChEMBL-NTD. Seven compounds from this set with predicted affinity to the active site were tested against in vitro cultures and three had reduced activity against a ΔPF3D7_1305500 parasite, suggesting PF3D7_1305500 is a potential target of the selected compounds. Identification of these compounds provides a novel starting point for a structure-based drug discovery strategy that moves us closer towards the discovery of new classes of clinical antimalarial drugs. These data suggest that MAPK phosphatases represent a potentially new class of P. falciparum drug target.
- ItemMapping Epitopes of the Plasmodium vivax Duffy Binding Protein with Naturally Acquired Inhibitory Antibodies(Infection and immunity, 2010) Chootong, Patchanee; Ntumngia, Francis B.; VanBuskirk, Kelley M.; Xainli, Jia; Cole-Tobian, Jennifer L.; Campbell, Christopher; Fraser, Tresa S.; King, Christopher L.; Adams, John H.Plasmodium vivax Duffy binding protein (DBP) is a merozoite microneme ligand vital for blood-stage infection, which makes it an important candidate vaccine for antibody-mediated immunity against vivax malaria. A differential screen with a linear peptide array compared the reactivities of noninhibitory and inhibitory high-titer human immune sera to identify target epitopes associated with protective immunity. Naturally acquired anti-DBP-specific serologic responses observed in the residents of a region of Papua New Guinea where P. vivax is highly endemic exhibited significant changes in DBP-specific titers over time. The anti-DBP functional inhibition for each serum ranged from complete inhibition to no inhibition even for high-titer responders to the DBP, indicating that epitope specificity is important. Inhibitory immune human antibodies identified specific B-cell linear epitopes on the DBP (SalI) ligand domain that showed significant correlations with inhibitory responses. Affinity-purified naturally acquired antibodies on these epitopes inhibited the DBP erythrocyte binding function greatly, confirming the protective value of specific epitopes. These results represent an important advance in our understanding of part of blood-stage immunity to P. vivax and some of the specific targets for vaccine-elicited antibody protection.