Advances in the optimization of central carbon metabolism in metabolic engineering

Abstract

Central carbon metabolism (CCM), including glycolysis, tricarboxylic acid cycle and the pentose phosphate pathway, is the most fundamental metabolic process in the activities of living organisms that maintains normal cellular growth. CCM has been widely used in microbial metabolic engineering in recent years due to its unique regulatory role in cellular metabolism. Using yeast and Escherichia coli as the representative organisms, we summarized the metabolic engineering strategies on the optimization of CCM in eukaryotic and prokaryotic microbial chassis, such as the introduction of heterologous CCM metabolic pathways and the optimization of key enzymes or regulatory factors, to lay the groundwork for the future use of CCM optimization in metabolic engineering. Furthermore, the bottlenecks in the application of CCM optimization in metabolic engineering and future application prospects are summarized.

Keywords: Central carbon metabolism; Escherichia coli; Metabolic engineering; Metabolic pathways; Microbial chassis; Yeast.

Fig. 1

The optimization of CCM by introduction of heterologous pathways to improve the carbon flux in S. cerevisiae. The black line represented glycolysis and pentose phosphate pathway, and the green line represented the tricarboxylic acid cycle. The red, blue and brown lines represented the implemented PHK, PDH and ACL pathways. The orange dot represented the products in CCM, while the purple dot represented ACP. G6P, Glucose 6-phosphate; F6P, Fructose-6-phosphate; F1,6P, Fructose-1,6-bisphosphate; GAP, Glyceraldehyde 3-phosphate; DHAP, Dihydroxyacetone phosphate; BPG, 1,3-Bisphosphoglycerate; 3PG, 3-Phosphoglycerate; 2PG, 2-Phosphoglycerate; PEP, Phosphoenolpyruvate; 6PG, 6-Phosphogluconate; 6PGL, 6-Phosphate glucono-1,5-lactone; X5P, Xylulose 5-phophate; Ru5P, Ribulose 5-phophate; R5P, Ribose 5-phosphate; E4P, Erythrose 4-phosphate; S7P, Sedoheptulose 7-phophate; ACP, Acetyl-phosphate; Acetyl-CoA, Acetyl coenzyme A; PK, Phosphoketolase; PTA, Phosphotransacetylase; PDH, Pyruvate dehydrogenase; ACL, ATP: citrate lyase

Fig. 2

The schematic diagram of the CCM with modulated enzymes in E. coli. The black line represented glycolysis and pentose phosphate pathway, and the green line represented the tricarboxylic acid cycle. The red line represented the glucose PTS system and the blue line represented the pathway catalyzed by modulated enzymes. The orange dot represented the products in CCM, while the purple dot represented the products in glucose PTS system. G6P, Glucose 6-phosphate; F6P, Fructose-6-phosphate; F1,6P, Fructose-1,6-bisphosphate; GAP, Glyceraldehyde 3-phosphate; DHAP, Dihydroxyacetone phosphate; 13DPG, 3-Phospho-D-glyceroyl phosphate; 3PG, 3-Phosphoglycerate; 2PG, 2-Phosphoglycerate; PEP, Phosphoenolpyruvate; 6PG15L, 6-Phospho D-glucono-1,5-lactone; X5P, Xylulose 5-phophate; Ru5P, Ribulose 5-phophate; R5P, Ribose 5-phosphate; E4P, Erythrose 4-phosphate; S7P, Sedoheptulose 7-phophate; EI, Phosphotransferases enzyme I; Hpr, Histidine phosphate carrier protein; EIIAB, Phosphotransferases enzyme II A and B; EIIC, Phosphotransferases enzyme II C; PGI, Glucose-6-phosphate isomerase; ZWF, Glucose-6-phosphate dehydrogenase; PYK, Pyruvate kinase; PEPC, Phosphoenolpyruvate carboxylase; TPIA, Triosephosphate isomerase; FBAA, Fructose-bisphosphate aldolase; CS, Citrate synthase; LDHA, Lactate dehydrogenase; POXB, Pyruvate oxidase