A Heterologous Expression System for Apicomplexa Genes

The phylum Apicomplexa is constituted exclusively by protozoan parasites, several of which pose a significant threat to public health. The apicomplexan Plasmodium falciparum is the ethiological agent of Malaria and can cause high mortality and morbidity in endemic areas. Toxoplasma, Cryptosporidium, and Cyclospora are also well known to public health authorities since they pose a threat to immunosuppressed individuals (e.g. transplanted and cancer patients), but also because sporadic outbreaks do occur (Cryptosporidium and Cyclospora) and because additional populations are at risk, i.e. pregnant women (Toxoplasma). Cryptosporidium, Cyclospora, and Toxoplasma are also listed as Category B Bioterrorist Threat Pathogens according to the Center of Disease Control, since infection occurs by oral transmission and the resistant oocysts shed by hosts can remain viable for long periods of time in soil and water. <P> With most of the genomes of these parasites available, it becomes evident the need for heterologous expression systems that can generate recombinant proteins, a step required for characterization of protein function, structural studies, production of antigen, screening and profiling drug candidates, and understanding action mechanisms. Available heterologous systems have been used with varying degrees of success; however, there is not a single expression system universally suitable for all applications and all have drawbacks in particular applications. <P> Hence, we propose to develop a heterologous system for production of Apicomplexa proteins using the protozoan P. marinus, a close relative of the Apicomplexa that is easily cultured in a full-defined cell-free medium. Although we have already a vector for transfection, in AIM1 we will incorporate into the vector a selectable marker and mine the P. marinus genome for targeting and secretion signals. <P> In AIM2, we will use selected Apicomplexa genes for proof of concept; these will include well-characterized apicomplexan genes as well as genes that have proven difficult to express in other systems. <P> We expect to overcome some of the past difficulties and to provide a valid alternative when the available heterologous expression systems do not result in expression, optimal protein yield, or functional proteins. The success of this system would result in apicomplexan proteins suitable for protein function studies, crystal structure determination, antigen production, and drug candidates, and will ultimately provide the tools required to more effectively fight and ameliorate the effects of these diseases. <P> PUBLIC HEALTH RELEVANCE: In order to develop new drugs and vaccines for fighting parasitic diseases, a more efficient system for producing recombinant proteins is required. We propose the protozoan Perkinsus marinus as a heterologous expression system for producing Apicomplexa proteins.