Importance of NADPH supply for improved <scp>L</scp>‐valine formation in <i>Corynebacterium glutamicum</i>

TLDR

Cofactor recycling is essential for amino acid synthesis. The study examined cofactor supply for L‑valine to identify targets for production improvement. Stoichiometric modeling of central carbon metabolism estimated cofactor influence and theoretical L‑valine yield, leading to deletion of phosphoglucoisomerase to realize an EM with a predicted yield of 0.86 mol Val per mol glucose. Three optimal L‑valine biosynthetic routes were identified, with the pentose phosphate pathway providing the most efficient NADPH regeneration; deletion of PGI increased intracellular NADPH, raised L‑valine yield from 0.49 to 0.67 mol Val per mol glucose, and reduced by‑product formation. © 2009 American Institute of Chemical Engineers Biotechnol.

Abstract

Abstract Cofactor recycling is known to be crucial for amino acid synthesis. Hence, cofactor supply was now analyzed for L ‐valine to identify new targets for an improvement of production. The central carbon metabolism was analyzed by stoichiometric modeling to estimate the influence of cofactors and to quantify the theoretical yield of L ‐valine on glucose. Three different optimal routes for L ‐valine biosynthesis were identified by elementary mode (EM) analysis. The modes differed mainly in the manner of NADPH regeneration, substantiating that the cofactor supply may be crucial for efficient L ‐valine production. Although the isocitrate dehydrogenase as an NADPH source within the tricarboxylic acid cycle only enables an L ‐valine yield of Y Val/Glc = 0.5 mol L ‐valine/mol glucose (mol Val/mol Glc), the pentose phosphate pathway seems to be the most promising NADPH source. Based on the theoretical calculation of EMs, the gene encoding phosphoglucoisomerase (PGI) was deleted to achieve this EM with a theoretical yield Y Val/Glc = 0.86 mol Val/mol Glc during the production phase. The intracellular NADPH concentration was significantly increased in the PGI‐deficient mutant. L ‐Valine yield increased from 0.49 ± 0.13 to 0.67 ± 0.03 mol Val/mol Glc, and, concomitantly, the formation of by‐products such as pyruvate was reduced. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010