Fig. 2

The metabolic pathway of l-pipecolic acid and the heterologous expression the key enzyme LCD. a The pathway and the strategies for metabolic engineering for l-pipecolic acid overproduction. The genes represented in red indicate increased flux by directly overexpression in the final recombinant strain E. coli BL21–dapA–lysC–lysA–pntAB–pipA. Enzymes encoded by the genes shown are: asd, aspartate semialdehyde dehydrogenase; dapA, dihydrodipicolinate synthase; dapB, dihydrodipicolinate reductase; dapC, N-succinyldiaminopimelate-aminotransferase; dapD, tetrahydrodipicolinate succinylase; dapE, N-succinyl-l-diaminopimelate desuccinylase; dapF, diaminopimelate epimerase; ddh, meso-diaminopimelate dehydrogenase from C. glutamicum; lysA, diaminopimelate decarboxylase; lysC, aspartate kinase III. b The detailed LCD catalytic process. The disassociated amine group are represented in red. c The heterologous expression of the key enzyme LCD. The over expressed LCD is about ~39 kD. Lane group 1 37 °C induced with 1 mM IPTG; Lane group 2 25 °C induced with 0.1 mM IPTG; Lane group 3 25 °C induced with 0.3 mM IPTG, Lane group 4 25 °C induced with 0.5 mM IPTG; Lane group 5 25 °C induced with 0.7 mM IPTG; Lane group 6 25 °C induced with 1 mM IPTG. The proteins in sediment is analyzed on the left while the protein in supernatant is analyzed on the right in every lane group