Fig. 1

Metabolic engineering strategies for L-cysteine biosynthesis in Escherichia coli: Through glycolysis (I, black arrows), the essential intermediate 3-phopsho-glycerate is produced, which is incorporated into L-serine biosynthesis (II, blue arrows). As a precursor amino acid, L-serine is used for the formation of L-cysteine (III, orange arrows). Alternatively, L-cysteine can be synthesised by the assimilatory sulphate reduction pathway (IV, yellow arrows). L-cysteine is transported out of the cell. Corresponding proteins for conversion of substrates are shown in black boxes. Boxes with green background represent expressed proteins within the synthetic plasmid constructs in this work. PtsI-III Phosphotransferase system I-III, PgI Glucose-6-phosphate isomerase, PfkA Phosphofructokinase 1, DhnA Fructose-bisphosphate aldolase, GapA Glyceraldehyde-3-phosphate dehydrogenase A, PgK Phosphoglycerate kinase, SerA D-3-phosphoglycerate dehydrogenase, SerC Phosphoserine aminotransferase, SerB Phosphoserine phosphatase, CysE Serine acetyltransferase, CysK Cysteine synthase A, CysA,P,U,W ATP-dependent sulphate/thiosulphate uptake system, CysM Cysteine synthase B, GrxA,B Glutaredoxin 1,2, NrdH Glutaredoxin-like protein, TrxAB Thioredoxin 1,2, EamA,B Cysteine exporter. Created with BioRender.com