Characterization of two phosphatase 2C domain-containing proteins PPM2A and PPM2B in Toxoplasma gondii.

Protein phosphatases Mg²⁺/Mn²⁺ dependent (PPMs), serine/threonine phosphatases, are widely distributed in apicomplexan parasites, and Toxoplasma gondii possesses the largest number of PPMs in the apicomplexan parasites. Though the function of some PPMs has been characterized in T. gondii, much less is known about two phosphatase 2C domain-containing proteins, PPM2A and PPM2B. PPM2A was identified as one of Toxoplasma Calmodulin's interacting proteins through proximity-based protein interaction BioID technology in the previous study, and PPM2B was the homolog of PPM2A in T. gondii. In this study, PPM2A was distributed in the whole tachyzoite of T. gondii, and PPM2B was mainly distributed in the cytoplasm by inserting a 10HA tag in the C-terminus of the two genes in the RH∆ku80 strain. PPM2A knockout (Δppm2a), PPM2B knockout (Δppm2b), and double knockout (ΔΔ) in RHΔhxgprt type I strain under CRISPR-Cas9 system did not result in intracellular replication defect. Besides, mouse experiments demonstrated that PPM2A, PPM2B, and double knockout did not reduce the pathogenicity of T. gondii compared with the RH∆hxgprt strain. However, the plaque size of these single knockout and double knockout strains were smaller than that in the control RH∆hxgprt strain. Our results provide new insight into the function of PPMs in the pathogenesis of T. gondii.