Deactivation and mislocalization of Toxoplasma gondii rhoptry protein 18 induced by a single amino acid mutation on the proton transport catalytic aspartic acid.

Rhoptry protein 18 (ROP18) is a major determinant of strain-specific virulence in Toxoplasma gondii. The kinase activity of ROP18 is required for acute virulence, while the aspartate in the catalytic loop of ROP18 is considered essential for phosphoryl transfer. We showed that a single amino acid mutation at the catalytic aspartate residue (D409A mutation) significantly altered ROP18 kinase activity in vitro, and abolished ROP18-mediated ATF6β degradation. Furthermore, the investigated single amino acid mutation in ROP18 led to alternation of subcellular localization of ROP18 protein. Our findings demonstrate that a single amino acid mutation on the proton transport catalytic aspartic acid induced alternations associated with ROP18 protein.