ROP2 from Toxoplasma gondii: a virulence factor with a protein-kinase fold and no enzymatic activity.

The ROP2 protein and its paralogs are important virulence factors secreted into the host cell by the parasite Toxoplasma gondii. Here we describe the crystal structure of a large and soluble domain of mature ROP2, representative of the ROP2-like protein family. This is a structure of a protein-kinase fold that is devoid of catalytic residues and does not bind ATP. Various structural extensions constitute a signature of this protein family and act to maintain the protein kinase in an open conformation. Our ROP2 structure rules out a previous structural model of attachment of ROP2-like proteins to the parasitophorous vacuole membrane. We propose an alternative mode of membrane attachment implicating basic and amphiphatic helices present in the flexible N terminus of ROP2.