Background: Eimeria is an important genus of apicomplexan parasites. A defining feature of these parasites is the oocyst, which is transmitted into the environment via the faeces of definitive hosts. The oocyst wall contains cross-linked, tyrosine-rich proteins and protects eight infectious sporozoites, housed in pairs within a second walled structure, the sporocyst. The biochemical basis for sporocyst wall formation is not known.
Findings: Here, we report the discovery of a novel tyrosine-rich protein, EtSWP1, in Eimeria tenella. Like the tyrosine-rich proteins of the oocyst wall, EtSWP1 is an intrinsically disordered protein with the tyrosine residues concentrated in a specific region of the protein, located immediately following the region of intrinsic disorder. We engineered E. tenella to express mCherry-tagged EtSWP1 and showed that the tagged protein localises specifically to sporocyst walls, indicating that the biochemistry of sporocyst wall assembly is analagous to that of oocyst walls.
Conclusions: Tyrosine-rich proteins are known to be key components of the oocyst wall and we now demonstrate, using gene and protein analyses combined with genetic manipulation, that a novel tyrosine-rich protein is specific for the sporocyst wall. This finding is important because it shows that the biochemistry of these two distinct walls is similar and, hence, brings targeted disruption of sporulation and, therefore, potential neutralisation of oocysts in the environment, a step closer.