Metabolite profiling of Saccharomyces cerevisiae with enhanced levels of S-adenosyl-L-methionine

S-adenosyl-L-methionine (SAM) is a metabolite that plays crucial roles in sustaining primary cellular functions. SAM is the main methyl-donor substrate for the majority of methylation reactions which are central in many different cellular functions, from histone methylation to mRNA methylation, and it is involved in the biosynthesis of several hormones and of polyamines. Due to SAM involvement in many physiological processes, possible shortage of SAM can be at the basis of a number of diseases. Dietary supplements of SAM in the form of nutraceuticals and in the form of drugs are available, wherein SAM is obtained via chemical synthesis or fermented yeast. The Saccharomyces cerevisiae enzyme Met13 is a Methylenetetrahydrofolate reductase, which is part of the folate-mediated one-carbon metabolism [1, 2] and plays a key-role in the regulation of this metabolic pathway being feed-back inhibited by SAM [3]. In this work, we engineered a laboratory strain of S. cerevisiae by introducing a chimeric version of the gene MET13 [3] which has been shown to be insensitive to SAM-dependent feed-back inhibition. The expression of the chimeric MET13 resulted into 40-fold increase of intracellular SAM levels. As the increase of SAM might be of interest also in the perspective of favouring certain bioprocesses besides the biosynthesis of SAM, this work aims at giving a picture of the metabolic changes occurring in S. cerevisiae upon accumulation of high levels of SAM. To this aim, we analysed the physiology and the intracellular metabolite profile of the engineered strain throughout batch fermentations. Metabolomics was used to determine the intracellular levels of folates and amino acids and identify crucial metabolic changes linked to the over-production of SAM. The information achieved in this study provides further knowledge on how yeast metabolism reacts upon specific perturbations and will be useful in order to lead future research aiming to increase the levels of specific metabolites.