title: Dissecting the interface between apicomplexan parasite and host cell: Insights from a divergent AMA-RON2 pair.
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 rhoptry neck protein 2 (RON2) family members localize to the host outer membrane and serve as ligands for apical membrane antigen (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 merozoite apical erythrocyte-binding ligand (MAEBL) proteins and forms a high-affinity, functional complex with its coevolved partner, TgRON2L1. High-resolution crystal structures of TgAMA4 in the apo and TgRON2L1-bound forms complemented with alanine scanning mutagenesis data reveal an unexpected 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 have 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 offer the potential for improved design of neutralizing therapeutics targeting a broad range of AMA-RON2 pairs and apicomplexan invasive stages.
authors.affiliation: Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, V8P 5C2, Canada;
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Parker
authors.affiliation: UMR 5235, CNRS Université Montpellier, 34095 Montpellier, France;
authors.forename: Diana M
authors.initials: DM
authors.lastname: Penarete-Vargas
authors.affiliation: Department of Biology, University of Victoria, Victoria, BC, V8P 5C2, Canada;
authors.forename: Phineas T
authors.initials: PT
authors.lastname: Hamilton
authors.affiliation: UMR 5235, CNRS Université Montpellier, 34095 Montpellier, France;
authors.forename: Amandine
authors.initials: A
authors.lastname: Guérin
authors.affiliation: Animal Parasitic Diseases Laboratory, Beltsville Agricultural Research Center, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705-2350;
authors.forename: Jitender P
authors.initials: JP
authors.lastname: Dubey
authors.affiliation: Department of Biology, University of Victoria, Victoria, BC, V8P 5C2, Canada;
authors.forename: Steve J
authors.initials: SJ
authors.lastname: Perlman
authors.affiliation: Department of Infectious, Parasitic and Immunomediated Diseases, Istituto Superiore di Sanità, Rome 00161, Italy.
authors.forename: Furio
authors.initials: F
authors.lastname: Spano
authors.affiliation: UMR 5235, CNRS Université Montpellier, 34095 Montpellier, France; mboulang@uvic.ca mylebrun@univ-montp2.fr.
authors.forename: Maryse
authors.initials: M
authors.lastname: Lebrun
authors.affiliation: Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, V8P 5C2, Canada; mboulang@uvic.ca mylebrun@univ-montp2.fr.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Boulanger
mesh_terms: D000818:Animals; D006790:Host-Parasite Interactions; D051379:Mice; D008958:Models, Molecular; D010271:Parasites / Q000502:physiology*; D010802:Phylogeny; D011485:Protein Binding; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism*; D014122:Toxoplasma / Q000378:metabolism*
chemical_list: D015800:Protozoan Proteins; C559757:rhoptry neck protein 2, Toxoplasma gondii
keywords: Apicomplexa; Toxoplasma gondii; X-ray crystallography; invasion; moving junction