Differential localisation of an Eimeria tenella aspartyl proteinase duringthe infection process

Aspartyl proteinases are essential for the survival of many pathogens. A si ngle copy gene in species of Eimeria encodes an aspartyl proteinase, which we propose should be called eimepsin to conform to the commonly used names of this family of proteinases. An epitope map, constructed using BIAcore te chnology, confirmed the specificity of 14 mAbs for eimepsin and defined fou r antigenic domains, which were conserved between native and recombinant fo rms of eimepsin. In resting sporozoites, mAb defining antigenic domains I a nd II stained the refractile body organelles, whereas those defining antige nic domains III and IV stained cytoplasmic granules. During host cell invas ion, the staining patterns of mAb defining antigenic domains I, III and IV changed dramatically with the apical tips of invading sporozoites becoming strongly stained. In contrast, mAb defining antigenic domain II continued t o stain only the refractile bodies. During early schizogony, mAb to all fou r domains stained the single fused refractile body, but when schizonts matu red, mAb to antigenic domains I, III and IV stained the apical tip of meroz oites whereas those to antigenic domain II continued to follow the developm ental redistribution of the refractile body. Irrespective of localisation, mAb to three antigenic domains recognised a polypeptide of 49 kDa, which fr om N-terminal sequencing corresponds to a mature form of eimepsin. Staining with fluorescent pepstatin localised a mature, active form of eimepsin to the refractile bodies of the sporozoite, schizont and first generation mero zoite. It remains to be determined whether eimepsin has a catalytic functio n within the refractile body or whether the activated enzyme is stored in t he refractile body so that it can be rapidly redistributed to the apical ti p during parasite invasion. (C) 2000 Australian Society for Parasitology In c. Published by Elsevier Science Ltd. All rights reserved.