Construction of cryptogein mutants, a proteinaceous elicitor from Phytophthora, with altered abilities to induce a defense reaction in tobacco cells

We prepared a series of cryptogein mutants, an elicitor from Phytophthora cryptogea, with altered abilities to bind sterols and fatty acids. The induction of the early events, i.e., synthesis of active oxygen species and pH changes, in suspension tobacco cells by these mutated proteins was proportional to their ability to bind sterols but not fatty acids. Although the cryptogein-sterol complex was suggested to be a form triggering a defense reaction in tobacco, some proteins unable to bind sterols induced the synthesis of active oxygen species and pH changes. The modeling experiments showed that conformational changes after the introduction of bulky residues into the omega loop of cryptogein resemble those induced by sterol binding. These changes may be necessary for the ability to trigger the early events by elicitins. However, the ability to stimulate necrosis in suspension tobacco cells and the expression of defense proteins in tobacco plants were linked neither to the lipid binding capacity nor to the capacity to provoke the early events. On the basis of these experiments and previous results, we propose that elicitins could stimulate two signal pathways. The first one induces necroses and the expression of pathogen-related proteins, includes tyrosine protein kinases and mitogen-activated protein kinases, and depends on the overall structure and charge distribution. The second type of interaction is mediated by phospholipase C and protein kinase C. It triggers the synthesis of active oxygen species and pH changes. This interaction depends on the ability of elicitins to bind sterols.

Recent developments in the production of human therapeutic proteins in eukaryotic algae

Antibody-based therapeutics have had great success over the last few years, and continue to be one of the fastest growing sectors of drug development. The efficacy and specificity of antibody-based drugs makes them ideal candidates for new drug development, but the specificity of these drugs comes from their complexity, and this complexity makes antibodies very expensive to produce. To address this problem, the authors have developed a system for the expression of recombinant proteins using the unicellular eukaryotic green algae, Chlamydomonas reinhardtii. As proof of concept, the authors have engineered microalgae to produce several forms of a human IgA antibody directed against herpes simplex virus. The expression of human monoclonal antibodies in C. reinhardtii offers an attractive alternative to traditional mammalian-based expression systems, as both the plastid and nuclear genomes are easily and quickly transformed, and the production of proteins in algae has an inherently low cost of capitalisation and production.