The Apicomplexa parasites Toxoplasma gondii and Plasmodium spp are responsible for a tremendous human health burden. Despites powerful genetic tools and high quality genomic databases, half of the predicted genes have no known function or similarity outside the Apicomplexa phylum. I will present two approaches to assign and study function of those novel proteins.
In T. gondii, cellular differentiation from the replicating stage to the bradyzoite tissue cyst stage is the underlying cause of chronic toxoplasmosis. The molecular mechanisms responsible for this developmental switch have long been sought. We identified 11 novel AP2 domain-containing proteins whose mRNA levels are induced in bradyzoites. Knock out, conditional expression, protein binding microarrays and transcriptomics defined one of those factors, AP2IX-9, as a transcription factor apparently acting as a gatekeeper to bradyzoite differentiation.
Despite strong evolutionary winds, recent transcriptome work reveals a similar gene expression cascade unfolding during the replication of Apicomplexa. We hypothesized that functionality, inferred by expression timing, could be utilized to identify novel pan-apicomplexan cell division cycle (panApi-CDC) genes. We identified 649 panApi-CDC genes of which ~25% encode unknown proteins. Those orthologs exhibit a remarkable preservation of timing and abundance suggesting important functions required for all apicomplexan cell division. Folding predictions revealed these proteins as highly disordered and, consistent with this observation, some act as interaction hubs as revealed by mining the Plasmodium interactome. Our ongoing experimental approach is validating and assigning function to those novel proteins.