Mp23, a Theileria parva transmembrane protein with homology to the protein disulfide isomerase family

Abstract

The protozoan parasite Theileria parva (Apicomplexa) causes the bovine disease East Coast Fever in endemic areas in Subsaharan Africa. The intralymphocytic schizont stage is largely responsible for the pathogenicity and induces a transformed phenotype in host cells [1]. Current evidence supports a model in which the schizont perturbs the immune response by inducing production of cytokines and stimulating the growth of parasitized cells [2]. We were interested to identify parasite proteins involved in parasite/host interaction and have described earlier a screening procedure for identification of schizont stage-exported proteins based on cell-free expression of cDNA and testing for translocation of protein products across endoplasmic reticulum (ER)-derived membranes [3]. A cDNA library of the schizont stage of T. parva was established in plasmid pBluescript II SK / (Stratagene) essentially as described [3]. In order to identify cDNAs encoding secretory and membrane proteins, which can be translocated across ER-derived microsomal membranes (rough microsomes (RM)), we screened 200 individual clones by an in vitro transcription/translation/translocation assay. Protection against subsequently added protease has been used as a criterion to identify those protein products that have crossed RM. Following this procedure, we found that clone 17 transcribed from the T7 RNA polymerase promoter