Metabolic control analysis for lysine synthesis using Corynebacterium glutamicum and experimental verification

Metabolic control analysis was carried out for the lysine biosynthetic pathway in Corynebacterium glutamicum ATCC 21253 using mechanism-based kinetic models developed for enzymatic reactions for this pathway. The rate-limiting steps during lysine production were determined with the aid of flux control coefficients, which indicated that the lysine synthesis flux is governed mainly by both aspartokinase and permease activity in the export system. Analyses indicated that an increase in the activity of aspartokinase would significantly alleviate its effect on the overall flux, and the limiting step is expected to shift to permease and other lysine synthetic enzymes. The influences of many participating precursors and cofactors on lysine synthesis flux were also investigated through the calculation of response coefficients for individual parameters. Although most parameters were not found to exert significant influences on lysine flux, extracellular lysine concentration was found to have a substantial effect on lysine production, and detailed analysis indicated that a decrease in the external lysine concentration will enhance the metabolite synthesis considerably and shift the control from export step to other steps. Although a decrease in external pH (pH0) seems to increase lysine flux, consideration of the export carrier concentration in response to external pH confirmed the optimum pH0 to be 7.0. Two types of recombinant strains overexpressing aspartokinase and dihydrodipicolinate synthase were constructed to verify the results obtained from metabolic sensitivity analysis.