Screening and characterization of apical membrane antigen 1 interacting proteins in Eimeria tenella

Avian coccidiosis is a widespread and economically significant disease of poultry. It is an enteric disease caused by several protozoan Eimeria species. Eimeria belongs to the phylum Apicomplexa, which exhibits an unusual mechanism of host cell invasion. During invasion of host cells, the protein apical membrane antigen 1 (AMA1) is essential for invasion of Toxoplasma gondii and Plasmodium. Contrary to the roles of AMA1 during host cell invasion in T. gondii and Plasmodium, the precise functions of Eimeria AMA1 (EtAMA1) are unclear. In order to study the functions of EtAMA1, a yeast two-hybrid cDNA library was constructed from E. tenella sporozoites. The EtAMA1 ectodomain was cloned into the pGBKT7 vector to construct the bait plasmid pGBKT7- EtAMA1. Autoactivation and toxicity of the bait protein in yeast cells were tested by comparison with the pGBKT7 empty vector. Expression of the bait protein was detected by western blots. The bait plasmid pGBKT7-EtAMA1 was used to screen yeast two-hybrid cDNA library from E. tenella sporozoites. After multiple screenings with high-screening-rate medium and exclusion of false-positive plasmids, positive preys were sequenced and analyzed using BLAST. We obtained 14 putative EtAMA1-interacting proteins including E. tenella acidic microneme protein2 (EtMIC2), E. tenella putative cystathionine beta-synthase, E. tenella Eimeria-specific protein, four E. tenella conserved hypothetical proteins (one in the serine/threonine protein kinase family) and seven unknown proteins. Gene Ontology analysis indicated that two known proteins were associated with metabolic process, pyridoxal phosphate binding and protein phosphorylation. Functional analysis indicated EtMIC2 was implicated in parasite motility, migration, recognition and invasion of host cells. The data suggested that EtAMA1 may be important during host cell invasion, but also involved in other biological processes.