L-citrulline is a nonprotein amino acid that plays an important role in human health and has great market demand. Although microbial cell factories have been widely used for biosynthesis, there are still challenges such as genetic instability and low efficiency in the biosynthesis of L-citrulline. In this study, an efficient, plasmid-free, non-inducible L-citrulline-producing strain of Escherichia coli BL21(DE3) was engineered by combined strategies. Firstly, a chassis strain capable of synthesizing L-citrulline was constructed by block of L-citrulline degradation and removal of feedback inhibition, with the L-citrulline titer of 0.43 g/L. Secondly, a push-pull-restrain strategy was employed to enhance the L-citrulline biosynthesis, which realized the L-citrulline titer of 6.0 g/L. Thirdly, the NADPH synthesis and L-citrulline transport were strengthened to promote the synthesis efficiency, which achieved the L-citrulline titer of 11.6 g/L. Finally, fed-batch fermentation was performed with the engineered strain in a 3 L fermenter, in which the L-citrulline titer reached 44.9 g/L. This study lays the foundation for the industrial production of L-citrulline and provides insights for the modification of other amino acid metabolic networks.
Citrulline/biosynthesis* ; Escherichia coli/genetics* ; Metabolic Engineering/methods* ; Fermentation ; NADP/biosynthesis*

NAD kinase catalyzes the phosphorylation of coenzyme I [NAD(H)] to form coenzyme II [NADP(H)], and NADPH is an important cofactor in L-isoleucine biosynthesis. In order to improve NADPH supply, ppnK, the gene encoding NAD kinase in Corynebacterium glutamicum was cloned and separately expressed in an L-isoleucine synthetic strain, Brevibacterium lactofermentum JHI3-156, by an inducible expression vector pDXW-8 and a constitutive expression vector pDXW-9. Compared with the control strain JHI3-156/pDXW-8, NAD kinase activity of the inducible ppnK-expressing strain JHI3-156/pDXW-8-ppnK was increased by 83.5%. NADP(H)/NAD(H) ratio was also increased by 63.8%. L-isoleucine biosynthesis was improved by 82.9%. Compared with the control strain JHI3-156/pDXW-9, NAD kinase activity of the constitutive ppnK-expressing strain JHI3-156/pDXW-9-ppnK was increased by 220%. NADP(H)/ NAD(H) ratio and NADPH concentration were increased by 134% and 21.7%, respectively. L-isoleucine biosynthesis was increased by 41.7%. These results demonstrate that NAD kinase can improve the coenzyme II supply and L-isoleucine biosynthesis, which would also be useful for biosynthesis of other amino acids.
Brevibacterium ; genetics ; metabolism ; Cloning, Molecular ; Corynebacterium glutamicum ; enzymology ; Isoleucine ; biosynthesis ; Metabolic Engineering ; NAD ; metabolism ; NADP ; metabolism ; Phosphotransferases (Alcohol Group Acceptor) ; genetics ; metabolism ; Recombinant Proteins ; genetics ; metabolism

The xylose reductase of Pichia stipitis is one of the most important enzymes. It can be used to build up recombinant Saccharomyces cerevisiae strain for utilizing xylose and producing ethanol. Intercellular redox imbalance caused by NADPH preference over NADH for Pichia stipitis xylose reductase (PsXR) has been considered to be one of the main factors for poor ethanol productivity. Some key amino acids of PsXR, which affect the activity or coenzyme preference, were investigated in our previous study. In this study, Lys21 were rational designed for site-directed mutagenesis to alter coenzyme specificity of PsXR from NADPH and NADH into single NADH. The wild gene and mutagenesis genes were ligated into pET28b, and were transferred into E.coli BL21(DE3). After induced by IPTG, the xylose reductases were purified. Purified mutants K21A (Lys21-->Ala), K21R(Lys21-->Arg) were characterized by steady-state kinetic analysis. The results showed that the coenzyme dependence of K21A was completely reversed to NADH.
Aldehyde Reductase ; metabolism ; Amino Acid Substitution ; genetics ; Coenzymes ; pharmacology ; Escherichia coli ; genetics ; metabolism ; Ethanol ; pharmacology ; Lysine ; genetics ; Mutagenesis, Site-Directed ; NAD ; metabolism ; NADP ; metabolism ; Pichia ; chemistry ; genetics ; metabolism ; Recombinant Proteins ; biosynthesis ; genetics ; metabolism ; Recombination, Genetic ; Xylose ; pharmacology

OBJECTIVETo study the expression of thymidine phosphorylase (TP), thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) mRNA in breast cancer and its correlation with prognosis.

METHODSExpression levels of TP, TS and DPD mRNA in 86 micro-selected breast cancer tissues and 9 normal breast tissues were detected by real-time quantitative PCR.

RESULTSThe median expression levels of TP, TS and DPD mRNA in tumor tissue and in normal tissues were 16.54, 0.38, 2.47 and 11.75, 0.25, 8.33, respectively, there were no significant differences (P >0.05). The expression levels of TP, TS and DPD mRNA showed no association with tumor size, lymph node metastasis, pathological grade and clinical stage, except that of DPD showed a negative association with patients' ages. There was no significant difference in disease-free survival or overall survival between the patients with high and low TP or DPD mRNA levels. Disease-free survival tends to be better in the patients with low TS mRNA level than those with high TS mRNA, but the difference was not significant (P=0.069), while the overall survival showed a statistically difference (59.00 month and 70.30 month) (P=0.0496).

CONCLUSIONThe expression level of TS mRNA may serve as a prognostic marker for breast cancer patients.

Adult ; Age Factors ; Aged ; Aged, 80 and over ; Breast ; enzymology ; Breast Neoplasms ; enzymology ; mortality ; pathology ; Dihydrouracil Dehydrogenase (NADP) ; biosynthesis ; genetics ; Disease-Free Survival ; Female ; Follow-Up Studies ; Humans ; Lymphatic Metastasis ; Middle Aged ; Neoplasm Staging ; Prognosis ; RNA, Messenger ; biosynthesis ; genetics ; Survival Rate ; Thymidine Phosphorylase ; biosynthesis ; genetics ; Thymidylate Synthase ; biosynthesis ; genetics