13C NMR based profiling unveils different α-ketoglutarate pools involved into glutamate and lysine synthesis in the milk yeast Kluyveromyces lactis

• Metabolic pathways are characterized by 13C NMR-based isotopomer analysis.
• α-Ketoglutarate (α-KG) pool involved in lysine synthesis is compartmentalized.
• α-KG pool for lysine synthesis is mitochondrial-independent.
• α-KG pool for lysine synthesis is PPP intermediates derived in rag8 cells.

BackgroundThe construction of efficient cell factories for the production of metabolites requires the rational improvement/engineering of the metabolism of microorganisms. The subject of this paper is directed towards the quantitative understanding of the respiratory/fermentative Kluyveromyces lactis yeast metabolism and its rag8 casein kinase mutant, taken as a model for all rag gene mutations.Methods13C NMR spectroscopy and [1,2-13C2]glucose were used as metabolic stable-isotope tracer to define the metabolic profiling of a K. lactis yeast and its derivative mutants.ResultsRag8 showed a decrease of all 13C glutamate fractional enrichments, except for [4-13C]glutamate that was higher than wild type ones. A decrease of TCA cycle flux in rag8 mutants and a contribution of a [4-13C]ketoglutarate pool not originating from mitochondria were suggested.13C lysine enrichments confirmed the presence of two compartmentalized α-ketoglutarate (α-KG) pools participating to glutamate and lysine synthesis.Moreover, an increased transaldolase, as compared to transketolase activity, was observed in the rag8 mutant by 13C NMR isotopomer analysis of alanine.Conclusions13C NMR-based isotopomer analysis showed the existence of different α-KG metabolic pools for glutamate and lysine biosynthesis. In the rag8 mutant, 13C labeled pentose phosphate intermediates participated in the synthesis of this compartmentalized α-KG pool.General significanceA compartmentalization of the α-KG pools involved in lysine biosynthesis has been revealed for the first time in K. lactis. Given its great impact in metabolic engineering field, its existence should be validated/compared with other yeasts and/or fungal species.