Abstract
Cestodes are unable to synthesize de novo most of their own membrane lipids, including cholesterol, and have to take them up from the host during an infection. The underlying molecular mechanisms are so far unknown. Here we report the identification and characterization of a novel gene, Emabp, which is expressed by larval stages and adults of the fox-tapeworm Echinococcus multilocularis. The encoded protein, EmABP, displays significant homologies to apolipoprotein A-I - binding protein (AI-BP) of mammalian origin and to metazoan YjeF_N domain proteins. Like mammalian AI-BP, EmABP carries an export-directing signal sequence which is absent in predicted AI-BP orthologs from the related flatworms Schistosoma japonicum and Schmidtea mediterranea. Using a specific antibody and immuno-precipitation techniques, we demonstrate that EmABP is secreted into the extra-parasitic environment and into hydatid fluid of in vitro cultivated metacestode vesicles. Furthermore, we show that apolipoprotein A-I (apoA-I), a major constituent of cholesterol-transporting high density lipoproteins, is present in hydatid fluid. By pull-down experiments, we demonstrate that recombinantly expressed, purified EmABP interacts with purified human apoA-I and is able to precipitate apoA-I from human serum. Based on these features, and on the suggested function of AI-BP in cholesterol transport in higher eukaryotes, we propose a role of EmABP in cholesterol- and lipid-uptake mechanisms of larval E. multilocularis.
Bernthaler, P