Location: Animal Parasitic Diseases LaboratoryTitle: Dissecting the interface between apicomplexan parasite and host cell: Insights from a divergent AMARON2 pair Author
Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2016
Publication Date: 1/20/2016
Citation: Parker, M.L., Penarete-Vargas, D.M., Hamilton, P.T., Guerin, A., Dubey, J.P., Perlman, S.J., Spano, F., Lebrun, M., Boulanger, M.J. 2016. Dissecting the interface between apicomplexan parasite and host cell: Insights from a divergent AMARON2 pair. Proceedings of the National Academy of Sciences. 113(2):398-403. Interpretive Summary: Toxoplasma gondii is a single celled parasite of worldwide distribution. It causes mental retardation and loss of vision in children whose mothers become infected during pregnancy, and abortion in livestock. This parasite can grow and destroy any cell of the body. Central to the pathogenesis of this and related parasites (e.g. Plasmodium, the cause of human malaria) is their ability to invade host cells through a junction formed by members of the Apical Membrane Antigen (AMA) and Rhoptry Neck Protein 2 (RON2) families localized to the parasite surface and host outer membrane, respectively. Here the authors structurally and functionally characterize T. gondii AMA4, a highly divergent AMA protein. Structural analyses of AMA4 in the apo and RON2L1 bound forms reveal a previously underappreciated level of molecular diversity at the parasite host cell interface. The results offer important insight into life-cycle stage dependent invasion strategies and yield a more comprehensive model of apicomplexan invasion. The paper will be of interest to biologists, and parasitologists.
Technical Abstract: Plasmodium falciparum and Toxoplasma gondii are widely studied parasites in phylum Apicomplexa and the etiological agents of severe human malaria and toxoplasmosis, respectively. These intracellular pathogens have evolved a sophisticated invasion strategy that relies on delivery of proteins into the host cell where parasite derived RON2 family members localize to the host outer membrane and serve as ligands for AMA family surface proteins displayed on the parasite. Recently we showed that T. gondii harbors a novel AMA designated as TgAMA4 that shows extreme sequence divergence from all characterized AMA family members. Here we show that sporozoite expressed TgAMA4 clusters in a distinct phylogenetic clade with Plasmodium MAEBL proteins and forms a high affinity, functional complex with its co-evolved partner, TgRON2L1. High-resolution crystal structures of TgAMA4 in the apo and TgRON2L1-bound forms complemented with alanine scanning mutagenesis data reveal a novel architecture and assembly mechanism relative to previously characterized AMA-RON2 complexes. Principally, TgAMA4 lacks both a deep surface groove and a key surface loop that has been established to govern RON2 ligand binding selectivity in other AMAs. Our study reveals a previously underappreciated level of molecular diversity at the parasite-host cell interface and offers intriguing insight into the adaptation strategies underlying sporozoite invasion. Moreover, our data offers the potential for improved design of neutralizing therapeutics targeting a broad range of AMA-RON2 pairs and apicomplexan invasive stages.