The Chlamydomonas chloroplast as a platform for production of therapeutic proteins.
Henry Taunt, Chloe McCann, and Saul Purton
Research Department of Structural and Molecular Biology, University College London, UK.
The chloroplast of Chlamydomonas represents an attractive platform for the production of therapeutic proteins, not least because of the availability of routine techniques for foreign gene expression in the chloroplast, the low cost of cultivation, and the lack of endotoxins or potentially infectious agents in the algal host. As a proof-of-concept, we have successfully produced human growth hormone (hGH) in Chlamydomonas using a newly designed expression vector, pASapI. This vector allows the creation of a perfect fusion at the ATG start codon between the promoter/5'UTR from atpA and the coding sequence of the foreign gene, and the targeting of the foreign gene into a neutral locus on the chloroplast genome downstream of psbH without the use of any antibiotic-based selectable marker. We are currently exploring whether various engineered changes to the expression vector or to the recipient strain result in improvements in the yield of hGH. In a related study, we have expressed the gene for a bacteriophage endolysin in Chlamydomonas. Endolysins hold great promise as antibacterials that are superior to traditional antibiotics since they can bring about the lysis of particular bacterial pathogen without affecting the body's natural flora, do not result in acquired resistance in the pathogen, and can kill pathogens that colonise mucosal surfaces. A series of in vitro studies is being carried using cell extracts prepared from the transgenic line to evaluate the efficacy of the endolysin in killing its target bacterium. The results of these studies will be presented.
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