bims-bramad 2020-09-27 papers

bims-bramad

Biomed News

on Branched chain amino acid catabolism in metabolic diseases

Issue of 2020‒09‒27
thirteen papers selected by
Dipsikha Biswas, Københavns Universitet

Multifaceted role of branched-chain amino acid metabolism in cancer.
Dietary intake of branched-chain amino acids and colorectal cancer risk.
Maternal and cord plasma branched-chain amino acids and child risk of attention-deficit hyperactivity disorder: a prospective birth cohort study.
Short-term branched-chain amino acid supplementation does not enhance vertical jump in professional volleyball players. A double-blind, controlled, randomized study.
Branched-Chain Fatty Acids-An Underexplored Class of Dairy-Derived Fatty Acids.
Urbanization in China is associated with pronounced perturbation of plasma metabolites.
The impact of Hayward green kiwifruit on dietary protein digestion and protein metabolism.
Role of Gut Microbiome and Microbial Metabolites in Alleviating Insulin Resistance After Bariatric Surgery.
Genomic Prediction Informed by Biological Processes Expands Our Understanding of the Genetic Architecture Underlying Free Amino Acid Traits in Dry Arabidopsis Seeds.
Global Response of Phaeobacter inhibens DSM 17395 to Deletion of Its 262-kb Chromid Encoding Antibiotic Synthesis.
Metabolic profiling of pre-gestational and gestational diabetes mellitus identifies novel predictors of pre-term delivery.
Safety, Tolerability, and Physiological Effects of AXA1665, a Novel Composition of Amino Acids, in Subjects With Child-Pugh A and B Cirrhosis.
High-yield production of L-valine in engineered Escherichia coli by a novel two-stage fermentation.

Oncogene. 2020 Sep 25.

Multifaceted role of branched-chain amino acid metabolism in cancer.

Hui Peng, Yingfei Wang, Weibo Luo.

Metabolic reprogramming fulfils increased nutrient demands and regulates numerous oncogenic processes in tumors, leading to tumor malignancy. Branched-chain amino acids (BCAAs, i.e., valine, leucine, and isoleucine) function as nitrogen donors to generate macromolecules such as nucleotides and are indispensable for human cancer cell growth. The cell-autonomous and non-autonomous roles of altered BCAA metabolism have been implicated in cancer progression and the key proteins in the BCAA metabolic pathway serve as possible prognostic and diagnostic biomarkers in human cancers. Here we summarize how BCAA metabolic reprogramming is regulated in cancer cells and how it influences cancer progression.

DOI: https://doi.org/10.1038/s41388-020-01480-z
Br J Nutr. 2020 Sep 23. 1-17

Dietary intake of branched-chain amino acids and colorectal cancer risk.

Marta Rossi, Federica Mascaretti, Maria Parpinel, Diego Serraino, Anna Crispo, Egidio Celentano, Attilio Giacosa, Carlo La Vecchia.

  An adequate intake of branched-chain amino acids (BCAAs) is required for protein synthesis and metabolic functions, including insulin metabolism. Emerging studies found positive associations between BCAAs and the risk of various diseases sharing etiological aspects with colorectal cancer (CRC), including type 2 diabetes, obesity, and pancreatic cancer.We investigated the relation between dietary BCAAs and CRC using data from a multicentric Italian case-control study, including 1953 cases of CRC (of these, 442 of sigmoid colon) and 4154 hospital controls with acute, non-neoplastic diseases. A validated food-frequency questionnaire was used to estimate the participants' usual diet and to assess dietary intakes of various nutrients, including energy, BCAAs and calcium. Odds ratio (ORs) and corresponding confidence intervals (CI) were computed by multiple logistic regression models adjusted for age, sex and other confounding factors, including total energy intake.BCAA intake was inversely related to CRC risk (OR for the highest versus the lowest quintile, 0.73; 95% CI, 0.55-0.97), but the association was attenuated after adjustment for calcium intake (OR, 0.90; 95% CI, 0.65-1.25). A linear inverse association with sigmoid colon cancer risk remained also after adjustment for other dietary factors, including calcium intake (OR, 0.49; 95% CI, 0.27-0.87).This study provides supporting evidence that higher levels of dietary BCAA intake are not associated with an increase of CRC risk, but confirms that they may be related to a reduced risk of sigmoid colon cancer.

Keywords:  Branched-chain amino acids; Colorectal cancer; Diet; Risk factor

DOI:  https://doi.org/10.1017/S0007114520003724
J Child Psychol Psychiatry. 2020 Sep 22.

Maternal and cord plasma branched-chain amino acids and child risk of attention-deficit hyperactivity disorder: a prospective birth cohort study.

Neha S Anand, Yuelong Ji, Guoying Wang, Xiumei Hong, Madeleine van der Rijn, Anne Riley, Colleen Pearson, Barry Zuckerman, Xiaobin Wang.

  BACKGROUND: Branched-chain amino acids (BCAA: leucine, isoleucine, and valine) are essential amino acids involved in biological functions of brain development and recently linked with autism. However, their role in attention-deficit hyperactivity disorder (ADHD) is not well-studied. We investigated individual and combined relationships of maternal plasma and newborn cord plasma BCAAs with childhood development of ADHD.METHODS: We utilized the Boston Birth Cohort, a predominantly urban, low-income, US minority population. Child developmental outcomes were defined in three mutually exclusive groups - ADHD, neurotypical (NT), or other developmental disabilities based on physician diagnoses per ICD-9 or 10 in medical records. The final sample included 626 children (299 ADHD, 327 NT) excluding other developmental disabilities. BCAAs were measured by liquid chromatography-tandem mass spectrometry. We used factor analysis to create composite scores of maternal and cord BCAA, which we divided into tertiles. Logistic regressions analyzed relationships between maternal or cord BCAA tertiles with child ADHD risk, controlling for maternal race, age, parity, smoking, education, low birth weight, preterm birth, and child sex. Additionally, we analyzed maternal and cord plasma BCAAs jointly on child ADHD risk.
RESULTS: Adjusted logistic regression found significantly increased odds of child ADHD diagnosis for the second (OR 1.63, 95% CI: 1.04, 2.54, p = .032) and third tertiles (OR 2.01, 95% CI: 1.28, 3.15, p = .002) of cord BCAA scores compared to the first tertile. This finding held for the third tertile when further adjusting for maternal BCAA score. There was no significant association between maternal BCAA score and child ADHD risk, nor a significant interaction between maternal and cord BCAA scores.
CONCLUSIONS: In this prospective US birth cohort, higher cord BCAA levels were associated with a greater risk of developing ADHD in childhood. These results have implications for further research into mechanisms of ADHD development and possible early life screening and interventions.

Keywords:  Attention-Deficit Hyperactivity Disorder; branched-chain amino acids; cord blood; metabolome

DOI:  https://doi.org/10.1111/jcpp.13332
Nutr Hosp. 2020 Sep 22.

Short-term branched-chain amino acid supplementation does not enhance vertical jump in professional volleyball players. A double-blind, controlled, randomized study.

Juan Pedro Martín-Martínez, Julio Calleja Gonzalez, José Carmelo Adsuar Sala, Santiago Gómez-Pomares, Jorge Carlos-Vivas, Jorge Pérez-Gómez.

To the best of the authors' knowledge, no previous studies have described the effect of branched-chain amino acids (BCAA) on vertical performance during a week in professional volleyball players. This study assessed BCAA supplementation for a week, aiming to improve vertical jump performance in male professional volleyball players. Twelve male volleyballers were randomly assigned to a BCAA group (n = 6) or a control group (n = 6). The BCAA group ingested 21 g over a week, 7 g per day on Monday, Wednesday, and Friday, before a volleyball training session, while the control group drank a placebo drink. Participants performed 8 maximal countermovement jumps (CMJ); the 3 CMJs on Monday and Wednesday were evaluated after warm-up, after plyometric training, and at the end of the training session; and the 2 CMJs on Friday were evaluated after warm-up, and at the end of the training session. Compared with baseline, significant differences in CMJ over the week were seen neither in the BCAA group (p < 0.000; SE = 0.31) nor between groups. The results indicated that 21 g of BCAA supplementation over a week did not improve vertical jump performance in professional volleyball players.

DOI: https://doi.org/10.20960/nh.03032
Nutrients. 2020 Sep 20. pii: E2875. [Epub ahead of print]12(9):

Branched-Chain Fatty Acids-An Underexplored Class of Dairy-Derived Fatty Acids.

Victoria M Taormina, Allison L Unger, Morgan R Schiksnis, Moises Torres-Gonzalez, Jana Kraft.

  Dairy fat and its fatty acids (FAs) have been shown to possess pro-health properties that can support health maintenance and disease prevention. In particular, branched-chain FAs (BCFAs), comprising approximately 2% of dairy fat, have recently been proposed as bioactive molecules contributing to the positive health effects associated with the consumption of full-fat dairy products. This narrative review evaluates human trials assessing the relationship between BCFAs and metabolic risk factors, while potential underlying biological mechanisms of BCFAs are explored through discussion of studies in animals and cell lines. In addition, this review details the biosynthetic pathway of BCFAs as well as the content and composition of BCFAs in common retail dairy products. Research performed with in vitro models demonstrates the potent, structure-specific properties of BCFAs to protect against inflammation, cancers, and metabolic disorders. Yet, human trials assessing the effect of BCFAs on disease risk are surprisingly scarce, and to our knowledge, no research has investigated the specific role of dietary BCFAs. Thus, our review highlights the critical need for scientific inquiry regarding dairy-derived BCFAs, and the influence of this overlooked FA class on human health.

Keywords:  anteiso; branched-chain amino acids; cancer; diabetes; inflammation; iso; metabolic diseases; milk; phytanic acid

DOI:  https://doi.org/10.3390/nu12092875
Metabolomics. 2020 Sep 19. 16(10): 103

Urbanization in China is associated with pronounced perturbation of plasma metabolites.

Yiqing Wang, Wei Sha, Huijun Wang, Annie Green Howard, Matthew C B Tsilimigras, Jiguo Zhang, Chang Su, Zhihong Wang, Bing Zhang, Anthony A Fodor, Penny Gordon-Larsen.

  INTRODUCTION: Urbanization is associated with major changes in environmental and lifestyle exposures that may influence metabolic signatures.OBJECTIVES: We investigated cross-sectional urban and rural differences in plasma metabolome analyzed by liquid chromatography/mass spectrometry platform in 500 Chinese adults aged 25-68 years from two neighboring southern Chinese provinces.
METHODS: We first examined the overall metabolome differences by urban and rural residential location, using Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) and random forest classification. We then tested the association between urbanization status and individual metabolites using a linear regression adjusting for age, sex, and province and conducted pathway analysis (Fisher's exact test) to identify metabolic pathways differed by urbanization status.
RESULTS: We observed distinct overall metabolome by urbanization status in OPLS-DA and random forest classification. Using linear regression, out of a total of 1108 unique metabolite features identified in this sample, we found that 266 metabolites were differed by urbanization status (positive false discovery rate-adjusted p-value, q-value < 0.05). For example, the following metabolites were positively associated with urbanization status: caffeine metabolites from xanthine metabolism, hazardous pollutants like 4-hydroxychlorothalonil and perfluorooctanesulfonate, and metabolites implicated in cardiometabolic diseases, such as branched-chain amino acids. In pathway analysis, we found that xanthine metabolism pathways differed by urbanization status (q-value = 1.64E-04).
CONCLUSION: We detected profound differences in host metabolites by urbanization status. Urban residents were characterized by metabolites signaling caffeine metabolism and toxic pollutants and metabolites on known pathways to cardiometabolic disease risks, compared to their rural counterparts. Our findings highlight the importance of considering urbanization in metabolomics analysis.

Keywords:  China; Plasma metabolomics; Pollution; Urbanization

DOI:  https://doi.org/10.1007/s11306-020-01724-9
Eur J Nutr. 2020 Sep 24.

The impact of Hayward green kiwifruit on dietary protein digestion and protein metabolism.

Sanghee Park, David D Church, Carlene Starck, Scott E Schutzler, Gohar Azhar, Il-Young Kim, Arny A Ferrando, Paul J Moughan, Robert R Wolfe.

  PURPOSE: The purpose of the study was to determine if an actinidin protease aids gastric digestion and the protein anabolic response to dietary protein.METHODS: Hayward green kiwifruit (containing an actinidin protease) and Hort 16A gold kiwifruit (devoid of actinidin protease) were given in conjunction with a beef meal to healthy older subjects. Twelve healthy older males (N = 6) and females (N = 6) were studied with a randomized, double-blinded, crossover design to assess muscle and whole-body protein metabolism before and after ingestion of kiwifruit and 100 g of ground beef. Subjects consumed 2 of each variety of kiwifruit daily for 14 d prior to each metabolic study, and again during each study with beef intake.
RESULTS: Hayward green kiwifruit consumption with beef resulted in a more rapid increase in peripheral plasma essential amino acid concentrations. There were significant time by kiwifruit intake interactions for plasma concentrations of EAAs, branched chain amino acids (BCAAs), and leucine (P < 0.01). However, there was no difference in the total amount of EAAs absorbed. As a result, there were no differences between kiwifruit in any of the measured parameters of protein kinetics.
CONCLUSION: Consumption of Hayward green kiwifruit, with a beef meal facilitates protein digestion and absorption of the constituent amino acids as compared to Hort 16A gold kiwifruit.
CLINICAL TRIAL: NCT04356573, April 21, 2020 "retrospectively registered".

Keywords:  Essential amino acids; Muscle protein synthetic rate; Stable isotope tracers; Whole-body protein turnover

DOI:  https://doi.org/10.1007/s00394-020-02363-5
Obes Surg. 2020 Sep 24.

Role of Gut Microbiome and Microbial Metabolites in Alleviating Insulin Resistance After Bariatric Surgery.

Mingfei Wang, Leping Li, Yuezhi Chen, Guodong Lian, Jinshen Wang, Jizhun Zhang, Keshu Shan, Liang Shang, Feng Tian, Changqing Jing.

  Insulin resistance (IR) is the most common pathophysiological change in patients with type 2 diabetes mellitus (T2DM). Several recent studies have suggested that the gut microbiome and microbial metabolites are involved in the pathogenesis of IR. Bariatric surgery, as an effective treatment for T2DM, can markedly alleviate IR through mechanisms that have not been elucidated. In this review, we summarize the current evidence on the changes in the gut microbiome and microbial metabolites (including lipopolysaccharide, short-chain fatty acids, branched-chain amino acids, aromatic amino acids, bile acids, methylamines, and indole derivatives) after bariatric surgery. Additionally, we discuss the mechanisms that correlate the changes in microbial metabolites with the postoperative alleviation of IR. Furthermore, we discuss the prospect of bariatric surgery as a treatment for T2DM.

Keywords:  Bariatric surgery; Gut microbiota; Insulin resistance; Microbial metabolite; T2DM

DOI:  https://doi.org/10.1007/s11695-020-04974-7
G3 (Bethesda). 2020 Sep 25. pii: g3.401240.2020. [Epub ahead of print]

Genomic Prediction Informed by Biological Processes Expands Our Understanding of the Genetic Architecture Underlying Free Amino Acid Traits in Dry Arabidopsis Seeds.

Sarah D Turner-Hissong, Kevin A Bird, Alexander E Lipka, Elizabeth G King, Timothy M Beissinger, Ruthie Angelovici.

  Plant growth, development, and nutritional quality depends upon amino acid homeostasis, especially in seeds. However, our understanding of the underlying genetics influencing amino acid content and composition remains limited, with only a few candidate genes and quantitative trait loci identified to date. Improved knowledge of the genetics and biological processes that determine amino acid levels will enable researchers to use this information for plant breeding and biological discovery. Towards this goal, we used genomic prediction to identify biological processes that are associated with, and therefore potentially influence, free amino acid (FAA) composition in seeds of the model plant Arabidopsis thaliana Markers were split into categories based on metabolic pathway annotations and fit using a genomic partitioning model to evaluate the influence of each pathway on heritability explained, model fit, and predictive ability. Selected pathways included processes known to influence FAA composition, albeit to an unknown degree, and spanned four categories: amino acid, core, specialized, and protein metabolism. Using this approach, we identified associations for pathways containing known variants for FAA traits, in addition to finding new trait-pathway associations. Markers related to amino acid metabolism, which are directly involved in the FAA regulation, improved predictive ability for branched chain amino acids and histidine. The use of genomic partitioning also revealed patterns across biochemical families, in which serine-derived FAAs were associated with protein related annotations and aromatic FAAs were associated with specialized metabolic pathways. Taken together, these findings provide evidence that genomic partitioning is a viable strategy to uncover the relative contributions of biological processes to FAA traits in seeds, offering a promising framework to guide hypothesis testing and narrow the search space for candidate genes.

Keywords:  Arabidopsis; MultiBLUP; amino acids; complex traits; genomic prediction

DOI:  https://doi.org/10.1534/g3.120.401240
Microb Physiol. 2020 Jul 24. 1-16

Global Response of Phaeobacter inhibens DSM 17395 to Deletion of Its 262-kb Chromid Encoding Antibiotic Synthesis.

Daniel Wünsch, Annemieke Strijkstra, Lars Wöhlbrand, Heike M Freese, Sabine Scheve, Christina Hinrichs, Kathleen Trautwein, Michael Maczka, Jörn Petersen, Stefan Schulz, Jörg Overmann, Ralf Rabus.

  The marine alphaproteobacterium Phaeobacter inhibens DSM 17395, a member of the Roseobacter group, was recently shown to markedly enhance growth upon deletion of its 262-kb chromid encoding biosynthesis of tropodithietic acid (TDA). To scrutinize the metabolic/regulatory adaptations that underlie enhanced growth of the Δ262 mutant, its transcriptome and proteome compared to the wild type were investigated in process-controlled bioreactors with Casamino Acids as growth substrate. Genome resequencing revealed only few additional genetic changes (a heterogenic insertion, prophage activation, and several point mutations) between wild type and Δ262 mutant, albeit with no conceivable effect on the studied growth physiology. The abundances of the vast majority of transcripts and proteins involved in the catabolic network for complete substrate oxidation to CO2 were found to be unchanged, suggesting that the enhanced amino acid utilization of the Δ262 mutant did not require elevated synthesis of most enzymes of the catabolic network. Similarly, constituents of genetic information processing and cellular processes remained mostly unchanged. In contrast, 426 genes displayed differential expression, of which 410 were localized on the 3.2-Mb chromosome, 5 on the 65-kb chromid, and 11 on the 78-kb chromid. Notably, the branched-chain amino transferase IlvE acting on rapidly utilized Val, Ile, and Leu was upregulated. Moreover, the transportome was reconfigured, as evidenced from increased abundances of transcripts and proteins of several uptake systems for amino acids and inorganic nutrients (e.g., phosphate). Some components of the respiratory chain were also upregulated, which correlates with the higher respiration rates of the Δ262 mutant. Furthermore, chromosomally encoded transcripts and proteins that are peripherally related to TDA biosynthesis (e.g., the serine acyl transferase CysE) were strongly downregulated in the Δ262 mutant. Taken together, these observations reflect adaptations to enhanced growth as well as the functional interconnectivity of the replicons of P. inhibens DSM 17395.

Keywords:  Amino acid metabolism; Chromids; Growth physiology; Phaeobacter inhibens; Plasmids; Roseobacter group; Tropodithietic acid synthesis

DOI:  https://doi.org/10.1159/000508591
J Transl Med. 2020 Sep 24. 18(1): 366

Metabolic profiling of pre-gestational and gestational diabetes mellitus identifies novel predictors of pre-term delivery.

Ilhame Diboun, Manjunath Ramanjaneya, Yasser Majeed, Lina Ahmed, Mohammed Bashir, Alexandra E Butler, Abdul Badi Abou-Samra, Stephen L Atkin, Nayef A Mazloum, Mohamed A Elrayess.

  BACKGROUND: Pregnant women with gestational diabetes mellitus (GDM) or type 2 diabetes mellitus (T2DM) are at increased risks of pre-term labor, hypertension and preeclampsia. In this study, metabolic profiling of blood samples collected from GDM, T2DM and control pregnant women was undertaken to identify potential diagnostic biomarkers in GDM/T2DM and compared to pregnancy outcome.METHODS: Sixty-seven pregnant women (21 controls, 32 GDM, 14 T2DM) in their second trimester underwent targeted metabolomics of plasma samples using tandem mass spectrometry with the Biocrates MxP® Quant 500 Kit. Linear regression models were used to identify the metabolic signature of GDM and T2DM, followed by generalized linear model (GLMNET) and Receiver Operating Characteristic (ROC) analysis to determine best predictors of GDM, T2DM and pre-term labor.
RESULTS: The gestational age at delivery was 2 weeks earlier in T2DM compared to GDM and controls and correlated negatively with maternal HbA1C and systolic blood pressure and positively with serum albumin. Linear regression models revealed elevated glutamate and branched chain amino acids in GDM + T2DM group compared to controls. Regression models also revealed association of lower levels of triacylglycerols and diacylglycerols containing oleic and linoleic fatty acids with pre-term delivery. A generalized linear model ROC analyses revealed that that glutamate is the best predictors of GDM compared to controls (area under curve; AUC = 0.81). The model also revealed that phosphatidylcholine diacyl C40:2, arachidonic acid, glycochenodeoxycholic acid, and phosphatidylcholine acyl-alkyl C34:3 are the best predictors of GDM + T2DM compared to controls (AUC = 0.90). The model also revealed that the triacylglycerols C17:2/36:4 and C18:1/34:1 are the best predictors of pre-term delivery (≤ 37 weeks) (AUC = 0.84).
CONCLUSIONS: This study highlights the metabolite alterations in women in their second trimester with diabetes mellitus and identifies predictive indicators of pre-term delivery. Future studies to confirm these associations in other cohorts and investigate their functional relevance and potential utilization for targeted therapies are warranted.

Keywords:  Gestational diabetes; Metabolomics; Pre-term delivery; Pregnancy; Type 2 diabetes

DOI:  https://doi.org/10.1186/s12967-020-02531-5
Clin Transl Gastroenterol. 2020 Aug;11(8): e00222

Safety, Tolerability, and Physiological Effects of AXA1665, a Novel Composition of Amino Acids, in Subjects With Child-Pugh A and B Cirrhosis.

Manu V Chakravarthy, Joel Neutel, Scharmen Confer, Peng Zhao, Noriaki Tatsuta, Sam Rebello, William C Comb, Michael Hamill, Tony Tramontin, Sean Carroll, Raffi Afeyan, Arun J Sanyal.

INTRODUCTION: AXA1665 is a novel investigational amino acid (AA) composition specifically designed to impact AA imbalance, ammoniagenesis, and dysregulated anabolic activity associated with cirrhosis.METHODS: This 2-part study examined AXA1665 effects on safety, tolerability, and hepatic/muscle physiology in subjects with Child-Pugh A and B cirrhosis. Part 1 established plasma ammonia and AA concentration baselines with a standardized protein supplement. Part 2 included two 15-day domiciled periods separated by a 14-day washout. In period 1, subjects were randomly distributed to 2 groups: AXA1665 14.7 g t.i.d. (group 1) or control t.i.d. (group 2). In period 2, subjects from group 1 crossed over to control and those in group 2 crossed over to AXA1665 4.9 g t.i.d. All subjects were maintained on standard of care (standardized meals; 30-minute daily, supervised, mandatory physical activity; and daily late-evening snack).
RESULTS: In parts 1 and 2, 23 and 17 participants were enrolled, respectively. Dose-dependent increases were observed in plasma concentrations of AXA1665-constituent AAs. Fasted branched-chain AA-to-aromatic AA and valine-to-phenylalanine ratios were both increased (AXA1665 14.7 g t.i.d. control-adjusted change: 44.3% ± 2.7% and 47.2% ± 3.9%, respectively; P < 0.0001). Despite provision of additional nitrogen, mean fasted plasma ammonia concentration at day 15 numerically decreased (-21.1% in AXA1665 14.7 g t.i.d. vs -3.8% in control; P > 0.05). AXA1665 14.7 g t.i.d. produced a leaner body composition and significantly decreased Liver Frailty Index at day 15 vs control (-0.70 ± 0.15 vs -0.14 ± 0.17; P < 0.05). AXA1665 was safe and well tolerated.
DISCUSSION: AXA1665 has potential to mitigate core metabolic derangements associated with cirrhosis.

DOI: https://doi.org/10.14309/ctg.0000000000000222
Metab Eng. 2020 Sep 19. pii: S1096-7176(20)30152-X. [Epub ahead of print]

High-yield production of L-valine in engineered Escherichia coli by a novel two-stage fermentation.

Yanan Hao, Qian Ma, Xiaoqian Liu, Xiaoguang Fan, Jiaxuan Men, Heyun Wu, Shuai Jiang, Daoguang Tian, Bo Xiong, Xixian Xie.

  L-valine is an essential amino acid and an important amino acid in the food and feed industry. The relatively low titer and low fermentation yield currently limit the large-scale application of L-valine. Here, we constructed a chromosomally engineered Escherichia coli to efficiently produce L-valine. First, the synthetic pathway of L-valine was enhanced by heterologous introduction of a feedback-resistant acetolactate acid synthase from Bacillus subtilis and overexpression of other two enzymes in the L-valine synthetic pathway. For efficient efflux of L-valine, an exporter from Corynebacterium glutamicum was subsequently introduced. Next, the precursor pyruvate pool was increased by knockout of GTP pyrophosphokinase and introduction of a ppGpp 3'-pyrophosphohydrolase mutant to facilitate the glucose uptake process. Finally, in order to improve the redox cofactor balance, acetohydroxy acid isomeroreductase was replaced by a NADH-preferring mutant, and branched-chain amino acid aminotransferase was replaced by leucine dehydrogenase from Bacillus subtilis. Redox cofactor balance enabled the strain to synthesize L-valine under oxygen-limiting condition, significantly increasing the yield in the presence of glucose. Two-stage fed-batch fermentation of the final strain in a 5 L bioreactor produced 84 g/L L-valine with a yield and productivity of 0.41 g/g glucose and 2.33 g/L/h, respectively. To the best of our knowledge, this is the highest L-valine titer and yield ever reported in E. coli. The systems metabolic engineering strategy described here will be useful for future engineering of E. coli strains for the industrial production of L-valine and related products.

Keywords:  Escherichia coli; L-valine; Metabolic engineering; Two-stage fermentation

DOI:  https://doi.org/10.1016/j.ymben.2020.09.007