Structures of monomeric and oligomeric forms of the <i>Toxoplasma gondii</i> perforin-like protein 1.

Abstract

<i>Toxoplasma</i> and <i>Plasmodium</i> are the parasitic agents of toxoplasmosis and malaria, respectively, and use perforin-like proteins (PLPs) to invade host organisms and complete their life cycles. The <i>Toxoplasma gondii</i> PLP1 (<i>Tg</i>PLP1) is required for efficient exit from parasitophorous vacuoles in which proliferation occurs. We report structures of the membrane attack complex/perforin (MACPF) and Apicomplexan PLP C-terminal β-pleated sheet (APCβ) domains of <i>Tg</i>PLP1. The MACPF domain forms hexameric assemblies, with ring and helix geometries, and the APCβ domain has a novel β-prism fold joined to the MACPF domain by a short linker. Molecular dynamics simulations suggest that the helical MACPF oligomer preserves a biologically important interface, whereas the APCβ domain binds preferentially through a hydrophobic loop to membrane phosphatidylethanolamine, enhanced by the additional presence of inositol phosphate lipids. This mode of membrane binding is supported by site-directed mutagenesis data from a liposome-based assay. Together, these structural and biophysical findings provide insights into the molecular mechanism of membrane targeting by <i>Tg</i>PLP1.