Metabolic engineering of Saccharomyces cerevisiae for improvement of antioxidant organic seleno-compounds biosynthesis

The unique redox chemistry of selenium (Se) makes this element an essential trace element for living organisms that use Se as detoxification system when dealing with oxidizing molecules that increase cell damages due to high oxidative stress level. Most of Se-proteins so far identified have actually been demonstrated to play important roles in preventing high oxidative stress level. Furthermore, low molecular weight organic Se-compounds derived from cellular metabolism of Se have been demonstrated to have high cancer prevention potential and to protect cells against oxidative stress. In particular, Se-methylselenocysteine (SeMCys), -glutamyl-Se-methylselenocysteine (G-SeMCys) and their derivative methylselenol (MeSeH) are the most effective Se-compounds in trial cancer therapies, when Se is supplied at supra-nutritional doses. SeMcys and G-SeMCys are present in some plants known as Se-accumulators belonging to Astragalus, Brassica and Allium families that, thanks to the action of Se-Methyltransferase (SeMT), convert Se-Cys in the better tolerated methylated form. However, increase of Se in-take to reach effective anti-cancer doses is not feasible by consuming a diet with natural Se compounds. Therefore, this research aims to enhance metabolic fluxes in the yeast Saccharomyces cerevisiae towards SeMCys biosynthesis through a metabolic engineering approach. To achieve this aim, yeast strains expressing the SeMT gene from Brassica oleracea at different levels have been constructed and characterized. Physiological studies, metabolic profiles and determination of the production of Se-compounds have been carried out in order to evaluate the function of the metabolic network after genetic perturbations and the ability of the S. cerevisiae cell factory to produce pharmacologically active LMW Se-compounds.