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Jung YJ, Park KH, Jang TY, Yoo SM. Gene expression regulation by modulating Hfq expression in coordination with tailor-made sRNA-based knockdown in Escherichia coli. J Biotechnol 2024; 388:1-10. [PMID: 38616040 DOI: 10.1016/j.jbiotec.2024.04.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2024] [Revised: 04/04/2024] [Accepted: 04/11/2024] [Indexed: 04/16/2024]
Abstract
The tailor-made synthetic sRNA-based gene expression knockdown system has demonstrated its efficacy in achieving pathway balancing in microbes, facilitating precise target gene repression and fine-tuned control of gene expression. This system operates under a competitive mode of gene regulation, wherein the tailor-made synthetic sRNA shares the intrinsic intracellular Hfq protein with other RNAs. The limited intracellular Hfq amount has the potential to become a constraining factor in the post-transcription regulation of sRNAs. To enhance the efficiency of the tailor-made sRNA gene expression regulation platform, we introduced an Hfq expression level modulation-coordinated sRNA-based gene knockdown system. This system comprises tailor-made sRNA expression cassettes that produce varying Hfq expression levels using different strength promoters. Modulating the expression levels of Hfq significantly improved the repressing capacity of sRNA, as evidenced by evaluations with four fluorescence proteins. In order to validate the practical application of this system, we applied the Hfq-modulated sRNA-based gene knockdown cassette to Escherichia coli strains producing 5-aminolevulinic acid and L-tyrosine. Diversifying the expression levels of metabolic enzymes through this cassette resulted in substantial increases of 74.6% in 5-aminolevulinic acid and 144% in L-tyrosine production. Tailor-made synthetic sRNA-based gene expression knockdown system, coupled with Hfq copy modulation, exhibits potential for optimizing metabolic fluxes through biosynthetic pathways, thereby enhancing the production yields of bioproducts.
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Affiliation(s)
- Yu Jung Jung
- School of Integrative Engineering, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea
| | - Keun Ha Park
- School of Integrative Engineering, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea
| | - Tae Yeong Jang
- School of Integrative Engineering, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea
| | - Seung Min Yoo
- School of Integrative Engineering, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea.
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2
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Kukil K, Lindberg P. Metabolic engineering of Synechocystis sp. PCC 6803 for the improved production of phenylpropanoids. Microb Cell Fact 2024; 23:57. [PMID: 38369470 PMCID: PMC10875765 DOI: 10.1186/s12934-024-02330-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Accepted: 02/09/2024] [Indexed: 02/20/2024] Open
Abstract
BACKGROUND Phenylpropanoids are a large group of plant secondary metabolites with various biological functions, derived from aromatic amino acids. Cyanobacteria are promising host organisms for sustainable production of plant phenylpropanoids. We have previously engineered Synechocystis sp. PCC 6803 to produce trans-cinnamic acid (tCA) and p-coumaric acid (pCou), the first intermediates of phenylpropanoid pathway, by overexpression of phenylalanine- and tyrosine ammonia lyases. In this study, we aimed to enhance the production of the target compounds tCA and pCou in Synechocystis. RESULTS We eliminated the 4-hydroxyphenylpyruvate dioxygenase (HPPD) activity, which is a competing pathway consuming tyrosine and, possibly, phenylalanine for tocopherol synthesis. Moreover, several genes of the terminal steps of the shikimate pathway were overexpressed alone or in operons, such as aromatic transaminases, feedback insensitive cyclohexadienyl dehydrogenase (TyrC) from Zymomonas mobilis and the chorismate mutase (CM) domain of the fused chorismate mutase/prephenate dehydratase enzyme from Escherichia coli. The obtained engineered strains demonstrated nearly 1.5 times enhanced tCA and pCou production when HPPD was knocked out compared to the parental production strains, accumulating 138 ± 3.5 mg L-1 of tCA and 72.3 ± 10.3 mg L-1 of pCou after seven days of photoautotrophic growth. However, there was no further improvement when any of the pathway genes were overexpressed. Finally, we used previously obtained AtPRM8 and TsPRM8 Synechocystis strains with deregulated shikimate pathway as a background for the overexpression of synthetic constructs with ppd knockout. CONCLUSIONS HPPD elimination enhances the tCA and pCou productivity to a similar extent. The use of PRM8 based strains as a background for overexpression of synthetic constructs, however, did not promote tCA and pCou titers, which indicates a tight regulation of the terminal steps of phenylalanine and tyrosine synthesis. This work contributes to establishing cyanobacteria as hosts for phenylpropanoid production.
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Affiliation(s)
- Kateryna Kukil
- Microbial Chemistry, Department of Chemistry - Ångström, Uppsala University, Box 523, SE 751 20, Uppsala, Sweden
| | - Pia Lindberg
- Microbial Chemistry, Department of Chemistry - Ångström, Uppsala University, Box 523, SE 751 20, Uppsala, Sweden.
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Ji A, Bao P, Ma A, Wei X. An Efficient Prephenate Dehydrogenase Gene for the Biosynthesis of L-tyrosine: Gene Mining, Sequence Analysis, and Expression Optimization. Foods 2023; 12:3084. [PMID: 37628083 PMCID: PMC10453860 DOI: 10.3390/foods12163084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Revised: 08/14/2023] [Accepted: 08/15/2023] [Indexed: 08/27/2023] Open
Abstract
L-tyrosine is a key precursor for synthesis of various functional substances, but the microbial production of L-tyrosine faces huge challenges. The development of new microbial chassis cell and gene resource is especially important for the biosynthesis of L-tyrosine. In this study, the optimal host strain Bacillus amyloliquefaciens HZ-12 was firstly selected by detecting the production capacity of L-tyrosine. Subsequently, the recombinant expression of 15 prephenate dehydrogenase genes led to the discovery of the best gene, Bao-tyrA from B. amyloliquefaciens HZ-12. After the overexpression of Bao-tyrA, the L-tyrosine yield of the recombinant strain HZ/P43-Bao-tyrA reach 411 mg/L, increased by 42% compared with the control strain (HZ/pHY300PLK). Moreover, the nucleic acid sequence and deduced amino acid sequence of the gene Bao-tyrA were analyzed, and their conservative sites and catalytic mechanisms were proposed. Finally, the expression of Bao-tyrA was regulated through a promoter and 5'-UTR sequence to obtain the optimal expression elements. Thereby, the maximum L-tyrosine yield of 475 mg/L was obtained from HZ/P43-UTR3-Bao-tyrA. B. amyloliquefaciens was applied for the first time to produce L-tyrosine, and the optimal prephenate dehydrogenase gene Bao-tyrA and corresponding expression elements were obtained. This study provides new microbial host and gene resource for the construction of efficient L-tyrosine chassis cells, and also lays a solid foundation for the production of various functional tyrosine derivatives.
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Affiliation(s)
- Anying Ji
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; (A.J.); (P.B.); (A.M.)
- Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, Wuhan 430070, China
- Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518000, China
| | - Pengfei Bao
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; (A.J.); (P.B.); (A.M.)
- Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, Wuhan 430070, China
- Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518000, China
| | - Aimin Ma
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; (A.J.); (P.B.); (A.M.)
- Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, Wuhan 430070, China
- Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518000, China
| | - Xuetuan Wei
- State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, China; (A.J.); (P.B.); (A.M.)
- Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, Wuhan 430070, China
- Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, Shenzhen 518000, China
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Zhang P, Gao J, Zhang H, Wang Y, Liu Z, Lee SY, Mao X. Metabolic engineering of Escherichia coli for the production of an antifouling agent zosteric acid. Metab Eng 2023; 76:247-259. [PMID: 36822462 DOI: 10.1016/j.ymben.2023.02.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Revised: 02/13/2023] [Accepted: 02/19/2023] [Indexed: 02/23/2023]
Abstract
Zosteric acid (ZA) is a Zostera species-derived, sulfated phenolic acid compound with antifouling activity and has gained much attention due to its nontoxic and biodegradable characteristics. However, the yield of Zostera species available for ZA extraction is limited by natural factors, such as season, latitude, light, and temperature. Here we report the development of metabolically engineered Escherichia coli strains capable of producing ZA from glucose and glycerol. First, intracellular availability of the sulfur donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS) was enhanced by knocking out the cysH gene responsible for PAPS consumption and overexpressing the genes required for PAPS biosynthesis. Co-overexpression of the genes encoding tyrosine ammonia-lyase, sulfotransferase 1A1, ATP sulfurylase, and adenosine 5'-phosphosulfate kinase constructed ZA producing strain with enhanced PAPS supply. Second, the feedback-resistant forms of aroG and tyrA genes (encoding 3-deoxy-d-arabinoheptulosonate 7-phosphate synthase and chorismate mutase, respectively) were overexpressed to relieve the feedback regulation of L-tyrosine biosynthesis. Third, the pykA gene involved in phosphoenolpyruvate-consuming reaction, the regulator gene tyrR, the competing pathway gene pheA, and the ptsHIcrr genes essential for the PEP:carbohydrate phosphotransferase system were deleted. Moreover, all genes involved in the shikimate pathway and the talA, tktA, and tktB genes in the pentose phosphate pathway were examined for ZA production. The PTS-independent glucose uptake system, the expression vector system, and the carbon source were also optimized. As a result, the best-performing strain successfully produced 1.52 g L-1 ZA and 1.30 g L-1p-hydroxycinnamic acid from glucose and glycerol in a 700 mL fed-batch bioreactor.
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Affiliation(s)
- Peichao Zhang
- Qingdao Key Laboratory of Food Biotechnology, College of Food Science and Engineering, Ocean University of China, Qingdao, China
| | - Jing Gao
- Qingdao Key Laboratory of Food Biotechnology, College of Food Science and Engineering, Ocean University of China, Qingdao, China
| | - Haiyang Zhang
- Qingdao Key Laboratory of Food Biotechnology, College of Food Science and Engineering, Ocean University of China, Qingdao, China
| | - Yongzhen Wang
- Qingdao Key Laboratory of Food Biotechnology, College of Food Science and Engineering, Ocean University of China, Qingdao, China
| | - Zhen Liu
- Qingdao Key Laboratory of Food Biotechnology, College of Food Science and Engineering, Ocean University of China, Qingdao, China
| | - Sang Yup Lee
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Four), BioProcess Engineering Research Center, Institute for the BioCentury, KAIST, Daejeon, Republic of Korea.
| | - Xiangzhao Mao
- Qingdao Key Laboratory of Food Biotechnology, College of Food Science and Engineering, Ocean University of China, Qingdao, China; Laboratory for Marine Drugs and Bioproducts of Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.
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Fermentative production of Vitamin E tocotrienols in Saccharomyces cerevisiae under cold-shock-triggered temperature control. Nat Commun 2020; 11:5155. [PMID: 33056995 PMCID: PMC7560618 DOI: 10.1038/s41467-020-18958-9] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Accepted: 09/22/2020] [Indexed: 01/18/2023] Open
Abstract
The diverse physiological functions of tocotrienols have listed them as valuable supplementations to α-tocopherol-dominated Vitamin E products. To make tocotrienols more readily available, tocotrienols-producing S. cerevisiae has been constructed by combining the heterologous genes from photosynthetic organisms with the endogenous shikimate pathway and mevalonate pathway. After identification and elimination of metabolic bottlenecks and enhancement of precursors supply, the engineered yeast can produce tocotrienols at yield of up to 7.6 mg/g dry cell weight (DCW). In particular, proper truncation of the N-terminal transit peptide from the plant-sourced enzymes is crucial. To further solve the conflict between cell growth and tocotrienols accumulation so as to enable high-density fermentation, a cold-shock-triggered temperature control system is designed for efficient control of two-stage fermentation, leading to production of 320 mg/L tocotrienols. The success in high-density fermentation of tocotrienols by engineered yeast sheds light on the potential of fermentative production of vitamin E tocochromanols. Tocotrienols are valuable supplementations to α-tocopherol-dominated Vitamin E products. Here, the authors engineer baker’s yeast by combining the heterologous genes from photosynthetic organisms with the endogenous pathway for the production of tocotrienols under cold-shock-triggered temperature control.
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Kim B, Binkley R, Kim HU, Lee SY. Metabolic engineering ofEscherichia colifor the enhanced production ofl‐tyrosine. Biotechnol Bioeng 2018; 115:2554-2564. [DOI: 10.1002/bit.26797] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 06/11/2018] [Accepted: 07/04/2018] [Indexed: 12/20/2022]
Affiliation(s)
- Byoungjin Kim
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Plus Program)Institute for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST)Daejeon Republic of Korea
| | - Robert Binkley
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Plus Program)Institute for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST)Daejeon Republic of Korea
| | - Hyun Uk Kim
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Plus Program)Institute for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST)Daejeon Republic of Korea
- Systems Metabolic Engineering and Systems Healthcare Cross‐Generation Collaborative Laboratory, KAISTDaejeon Republic of Korea
- BioInformatics Research Center, KAISTDaejeon Republic of Korea
| | - Sang Yup Lee
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Plus Program)Institute for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST)Daejeon Republic of Korea
- Systems Metabolic Engineering and Systems Healthcare Cross‐Generation Collaborative Laboratory, KAISTDaejeon Republic of Korea
- BioInformatics Research Center, KAISTDaejeon Republic of Korea
- BioProcess Engineering Research Center, KAISTDaejeon Republic of Korea
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7
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Schenck CA, Men Y, Maeda HA. Conserved Molecular Mechanism of TyrA Dehydrogenase Substrate Specificity Underlying Alternative Tyrosine Biosynthetic Pathways in Plants and Microbes. Front Mol Biosci 2017; 4:73. [PMID: 29164132 PMCID: PMC5681985 DOI: 10.3389/fmolb.2017.00073] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 10/24/2017] [Indexed: 12/03/2022] Open
Abstract
L-Tyrosine (Tyr) is an aromatic amino acid synthesized de novo in plants and microbes. In animals, Tyr must be obtained through their diet or synthesized from L-phenylalanine. In addition to protein synthesis, Tyr serves as the precursor of neurotransmitters (e.g., dopamine and epinephrine) in animals and of numerous plant natural products, which serve essential functions in both plants and humans (e.g., vitamin E and morphine). Tyr is synthesized via two alternative routes mediated by a TyrA family enzyme, prephenate, or arogenate dehydrogenase (PDH/TyrAp or ADH/TyrAa), typically found in microbes and plants, respectively. Although ADH activity is also found in some bacteria, the origin of arogenate-specific TyrAa enzymes is unknown. We recently identified an acidic Asp222 residue that confers ADH activity in plant TyrAs. In this study, structure-guided phylogenetic analyses identified bacterial homologs, closely-related to plant TyrAs, that also have an acidic 222 residue and ADH activity. A more distant archaeon TyrA that preferred PDH activity had a non-acidic Gln, whose substitution to Glu introduced ADH activity. These results indicate that the conserved molecular mechanism operated during the evolution of arogenate-specific TyrAa in both plants and microbes.
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Affiliation(s)
- Craig A Schenck
- Department of Botany, University of Wisconsin-Madison, Madison, WI, United States
| | - Yusen Men
- Department of Botany, University of Wisconsin-Madison, Madison, WI, United States
| | - Hiroshi A Maeda
- Department of Botany, University of Wisconsin-Madison, Madison, WI, United States
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8
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Shlaifer I, Quashie PK, Kim HY, Turnbull JL. Biochemical characterization of TyrA enzymes from Ignicoccus hospitalis and Haemophilus influenzae: A comparative study of the bifunctional and monofunctional dehydrogenase forms. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2016; 1865:312-320. [PMID: 28025081 DOI: 10.1016/j.bbapap.2016.12.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Revised: 11/23/2016] [Accepted: 12/22/2016] [Indexed: 02/08/2023]
Abstract
Biosynthesis of l-tyrosine (l-Tyr) is directed by the interplay of two enzymes. Chorismate mutase (CM) catalyzes the rearrangement of chorismate to prephenate, which is then converted to hydroxyphenylpyruvate by prephenate dehydrogenase (PD). This work reports the first characterization of the independently expressed PD domain of bifunctional CM-PD from the crenarchaeon Ignicoccus hospitalis and the first functional studies of both full-length CM-PD and the PD domain from the bacterium Haemophilus influenzae. All proteins were hexa-histidine tagged, expressed in Escherichia coli and purified. Expression and purification of I. hospitalis CM-PD generated a degradation product identified as a PD fragment lacking the protein's first 80 residues, Δ80CM-PD. A comparable stable PD domain could also be generated by limited tryptic digestion of this bifunctional enzyme. Thus, Δ80CM-PD constructs were prepared in both organisms. CM-PD and Δ80CM-PD from both organisms were dimeric and displayed the predicted enzymatic activities and thermal stabilities in accord with their hyperthermophilic and mesophilic origins. In contrast with H. influenzae PD activity which was NAD+-specific and displayed >75% inhibition with 50μM l-Tyr, I. hospitalis PD demonstrated dual cofactor specificity with a preference for NADP+ and an insensitivity to l-Tyr. These properties are consistent with a model of the I. hospitalis PD domain based on the previously reported structure of the H. influenzae homolog. Our results highlight the similarities and differences between the archaeal and bacterial TyrA proteins and reveal that the PD activity of both prokaryotes can be successfully mapped to a functionally independent unit.
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Affiliation(s)
- Irina Shlaifer
- Department of Chemistry and Biochemistry and the Centre for Structural and Functional Genomics, Concordia University, 7141 Sherbrooke St. West, Montréal, Québec H4B 1R6, Canada
| | - Peter Kojo Quashie
- Department of Chemistry and Biochemistry and the Centre for Structural and Functional Genomics, Concordia University, 7141 Sherbrooke St. West, Montréal, Québec H4B 1R6, Canada
| | - Hyun Young Kim
- Department of Chemistry and Biochemistry and the Centre for Structural and Functional Genomics, Concordia University, 7141 Sherbrooke St. West, Montréal, Québec H4B 1R6, Canada
| | - Joanne L Turnbull
- Department of Chemistry and Biochemistry and the Centre for Structural and Functional Genomics, Concordia University, 7141 Sherbrooke St. West, Montréal, Québec H4B 1R6, Canada.
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9
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Shlaifer I, Turnbull JL. Characterization of two key enzymes for aromatic amino acid biosynthesis in symbiotic archaea. Extremophiles 2016; 20:503-14. [DOI: 10.1007/s00792-016-0840-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Accepted: 05/15/2016] [Indexed: 10/21/2022]
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10
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Gold ND, Gowen CM, Lussier FX, Cautha SC, Mahadevan R, Martin VJJ. Metabolic engineering of a tyrosine-overproducing yeast platform using targeted metabolomics. Microb Cell Fact 2015; 14:73. [PMID: 26016674 PMCID: PMC4458059 DOI: 10.1186/s12934-015-0252-2] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Accepted: 05/06/2015] [Indexed: 11/30/2022] Open
Abstract
Background L-tyrosine is a common precursor for a wide range of valuable secondary metabolites, including benzylisoquinoline alkaloids (BIAs) and many polyketides. An industrially tractable yeast strain optimized for production of L-tyrosine could serve as a platform for the development of BIA and polyketide cell factories. This study applied a targeted metabolomics approach to evaluate metabolic engineering strategies to increase the availability of intracellular L-tyrosine in the yeast Saccharomyces cerevisiae CEN.PK. Our engineering strategies combined localized pathway engineering with global engineering of central metabolism, facilitated by genome-scale steady-state modelling. Results Addition of a tyrosine feedback resistant version of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase Aro4 from S. cerevisiae was combined with overexpression of either a tyrosine feedback resistant yeast chorismate mutase Aro7, the native pentafunctional arom protein Aro1, native prephenate dehydrogenase Tyr1 or cyclohexadienyl dehydrogenase TyrC from Zymomonas mobilis. Loss of aromatic carbon was limited by eliminating phenylpyruvate decarboxylase Aro10. The TAL gene from Rhodobacter sphaeroides was used to produce coumarate as a simple test case of a heterologous by-product of tyrosine. Additionally, multiple strategies for engineering global metabolism to promote tyrosine production were evaluated using metabolic modelling. The T21E mutant of pyruvate kinase Cdc19 was hypothesized to slow the conversion of phosphoenolpyruvate to pyruvate and accumulate the former as precursor to the shikimate pathway. The ZWF1 gene coding for glucose-6-phosphate dehydrogenase was deleted to create an NADPH deficiency designed to force the cell to couple its growth to tyrosine production via overexpressed NADP+-dependent prephenate dehydrogenase Tyr1. Our engineered Zwf1− strain expressing TYRC ARO4FBR and grown in the presence of methionine achieved an intracellular L-tyrosine accumulation up to 520 μmol/g DCW or 192 mM in the cytosol, but sustained flux through this pathway was found to depend on the complete elimination of feedback inhibition and degradation pathways. Conclusions Our targeted metabolomics approach confirmed a likely regulatory site at DAHP synthase and identified another possible cofactor limitation at prephenate dehydrogenase. Additionally, the genome-scale metabolic model identified design strategies that have the potential to improve availability of erythrose 4-phosphate for DAHP synthase and cofactor availability for prephenate dehydrogenase. We evaluated these strategies and provide recommendations for further improvement of aromatic amino acid biosynthesis in S. cerevisiae. Electronic supplementary material The online version of this article (doi:10.1186/s12934-015-0252-2) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Nicholas D Gold
- Department of Biology and Centre for Structural and Functional Genomics, Concordia University, 7141 Sherbrooke West, Montreal, QC, H4B 1R6, Canada.
| | - Christopher M Gowen
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON, M5S 3E5, Canada.
| | - Francois-Xavier Lussier
- Department of Biology and Centre for Structural and Functional Genomics, Concordia University, 7141 Sherbrooke West, Montreal, QC, H4B 1R6, Canada.
| | - Sarat C Cautha
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON, M5S 3E5, Canada.
| | - Radhakrishnan Mahadevan
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, ON, M5S 3E5, Canada. .,Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, ON, M5S 3G9, Canada.
| | - Vincent J J Martin
- Department of Biology and Centre for Structural and Functional Genomics, Concordia University, 7141 Sherbrooke West, Montreal, QC, H4B 1R6, Canada.
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Graindorge M, Giustini C, Kraut A, Moyet L, Curien G, Matringe M. Three different classes of aminotransferases evolved prephenate aminotransferase functionality in arogenate-competent microorganisms. J Biol Chem 2013; 289:3198-208. [PMID: 24302739 DOI: 10.1074/jbc.m113.486480] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The aromatic amino acids phenylalanine and tyrosine represent essential sources of high value natural aromatic compounds for human health and industry. Depending on the organism, alternative routes exist for their synthesis. Phenylalanine and tyrosine are synthesized either via phenylpyruvate/4-hydroxyphenylpyruvate or via arogenate. In arogenate-competent microorganisms, an aminotransferase is required for the transamination of prephenate into arogenate, but the identity of the genes is still unknown. We present here the first identification of prephenate aminotransferases (PATs) in seven arogenate-competent microorganisms and the discovery that PAT activity is provided by three different classes of aminotransferase, which belong to two different fold types of pyridoxal phosphate enzymes: an aspartate aminotransferase subgroup 1β in tested α- and β-proteobacteria, a branched-chain aminotransferase in tested cyanobacteria, and an N-succinyldiaminopimelate aminotransferase in tested actinobacteria and in the β-proteobacterium Nitrosomonas europaea. Recombinant PAT enzymes exhibit high activity toward prephenate, indicating that the corresponding genes encode bona fide PAT. PAT functionality was acquired without other modification of substrate specificity and is not a general catalytic property of the three classes of aminotransferases.
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Affiliation(s)
- Matthieu Graindorge
- From the Commissariat à l'Energie Atomique, Direction des Sciences du Vivant, institut de Recherches en Technologies et en Sciences pour le Vivant, Laboratoire de Physiologie Cellulaire et Végétale, F-38054 Grenoble, France
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Chávez-Béjar MI, Báez-Viveros JL, Martínez A, Bolívar F, Gosset G. Biotechnological production of l-tyrosine and derived compounds. Process Biochem 2012. [DOI: 10.1016/j.procbio.2012.04.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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13
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Ku HK, Do NH, Song JS, Choi S, Yeon SH, Shin MH, Kim KJ, Park SR, Park IY, Kim SK, Lee SJ. Crystal structure of prephenate dehydrogenase from Streptococcus mutans. Int J Biol Macromol 2011; 49:761-6. [PMID: 21798280 DOI: 10.1016/j.ijbiomac.2011.07.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2011] [Revised: 07/11/2011] [Accepted: 07/11/2011] [Indexed: 10/17/2022]
Abstract
Prephenate dehydrogenase (PDH) is a bacterial enzyme that catalyzes conversion of prephenate to 4-hydroxyphenylpyruvate through the oxidative decarboxylation pathway for tyrosine biosynthesis. This enzymatic pathway exists in prokaryotes but is absent in mammals, indicating that it is a potential target for the development of new antibiotics. The crystal structure of PDH from Streptococcus mutans in a complex with NAD(+) shows that the enzyme exists as a homo-dimer, each monomer consisting of two domains, a modified nucleotide binding N-terminal domain and a helical prephenate C-terminal binding domain. The latter is the dimerization domain. A structural comparison of PDHs from mesophilic S. mutans and thermophilic Aquifex aeolicus showed differences in the long loop between β6 and β7, which may be a reason for the high K(m) values of PDH from Streptococcus mutans.
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Affiliation(s)
- Hyung-Keun Ku
- Division of Metrology for Quality of Life, Department of Bio-Analytical Science, University of Science & Technology, Daejeon, Republic of Korea
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14
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Chiu HJ, Abdubek P, Astakhova T, Axelrod HL, Carlton D, Clayton T, Das D, Deller MC, Duan L, Feuerhelm J, Grant JC, Grzechnik A, Han GW, Jaroszewski L, Jin KK, Klock HE, Knuth MW, Kozbial P, Krishna SS, Kumar A, Marciano D, McMullan D, Miller MD, Morse AT, Nigoghossian E, Okach L, Reyes R, Tien HJ, Trame CB, van den Bedem H, Weekes D, Xu Q, Hodgson KO, Wooley J, Elsliger MA, Deacon AM, Godzik A, Lesley SA, Wilson IA. The structure of Haemophilus influenzae prephenate dehydrogenase suggests unique features of bifunctional TyrA enzymes. Acta Crystallogr Sect F Struct Biol Cryst Commun 2010; 66:1317-25. [PMID: 20944228 PMCID: PMC2954222 DOI: 10.1107/s1744309110021688] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2010] [Accepted: 06/07/2010] [Indexed: 11/10/2022]
Abstract
Chorismate mutase/prephenate dehydrogenase from Haemophilus influenzae Rd KW20 is a bifunctional enzyme that catalyzes the rearrangement of chorismate to prephenate and the NAD(P)(+)-dependent oxidative decarboxylation of prephenate to 4-hydroxyphenylpyruvate in tyrosine biosynthesis. The crystal structure of the prephenate dehydrogenase component (HinfPDH) of the TyrA protein from H. influenzae Rd KW20 in complex with the inhibitor tyrosine and cofactor NAD(+) has been determined to 2.0 Å resolution. HinfPDH is a dimeric enzyme, with each monomer consisting of an N-terminal α/β dinucleotide-binding domain and a C-terminal α-helical dimerization domain. The structure reveals key active-site residues at the domain interface, including His200, Arg297 and Ser179 that are involved in catalysis and/or ligand binding and are highly conserved in TyrA proteins from all three kingdoms of life. Tyrosine is bound directly at the catalytic site, suggesting that it is a competitive inhibitor of HinfPDH. Comparisons with its structural homologues reveal important differences around the active site, including the absence of an α-β motif in HinfPDH that is present in other TyrA proteins, such as Synechocystis sp. arogenate dehydrogenase. Residues from this motif are involved in discrimination between NADP(+) and NAD(+). The loop between β5 and β6 in the N-terminal domain is much shorter in HinfPDH and an extra helix is present at the C-terminus. Furthermore, HinfPDH adopts a more closed conformation compared with TyrA proteins that do not have tyrosine bound. This conformational change brings the substrate, cofactor and active-site residues into close proximity for catalysis. An ionic network consisting of Arg297 (a key residue for tyrosine binding), a water molecule, Asp206 (from the loop between β5 and β6) and Arg365' (from the additional C-terminal helix of the adjacent monomer) is observed that might be involved in gating the active site.
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Affiliation(s)
- Hsiu-Ju Chiu
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - Polat Abdubek
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Protein Sciences Department, Genomics Institute of the Novartis Research Foundation, San Diego, CA, USA
| | - Tamara Astakhova
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Center for Research in Biological Systems, University of California, San Diego, La Jolla, CA, USA
| | - Herbert L. Axelrod
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - Dennis Carlton
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Thomas Clayton
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Debanu Das
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - Marc C. Deller
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Lian Duan
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Center for Research in Biological Systems, University of California, San Diego, La Jolla, CA, USA
| | - Julie Feuerhelm
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Protein Sciences Department, Genomics Institute of the Novartis Research Foundation, San Diego, CA, USA
| | - Joanna C. Grant
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Protein Sciences Department, Genomics Institute of the Novartis Research Foundation, San Diego, CA, USA
| | - Anna Grzechnik
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Gye Won Han
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Lukasz Jaroszewski
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Center for Research in Biological Systems, University of California, San Diego, La Jolla, CA, USA
- Program on Bioinformatics and Systems Biology, Sanford–Burnham Medical Research Institute, La Jolla, CA, USA
| | - Kevin K. Jin
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - Heath E. Klock
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Protein Sciences Department, Genomics Institute of the Novartis Research Foundation, San Diego, CA, USA
| | - Mark W. Knuth
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Protein Sciences Department, Genomics Institute of the Novartis Research Foundation, San Diego, CA, USA
| | - Piotr Kozbial
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Program on Bioinformatics and Systems Biology, Sanford–Burnham Medical Research Institute, La Jolla, CA, USA
| | - S. Sri Krishna
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Center for Research in Biological Systems, University of California, San Diego, La Jolla, CA, USA
- Program on Bioinformatics and Systems Biology, Sanford–Burnham Medical Research Institute, La Jolla, CA, USA
| | - Abhinav Kumar
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - David Marciano
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Daniel McMullan
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Protein Sciences Department, Genomics Institute of the Novartis Research Foundation, San Diego, CA, USA
| | - Mitchell D. Miller
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - Andrew T. Morse
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Center for Research in Biological Systems, University of California, San Diego, La Jolla, CA, USA
| | - Edward Nigoghossian
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Protein Sciences Department, Genomics Institute of the Novartis Research Foundation, San Diego, CA, USA
| | - Linda Okach
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Protein Sciences Department, Genomics Institute of the Novartis Research Foundation, San Diego, CA, USA
| | - Ron Reyes
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - Henry J. Tien
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Christine B. Trame
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - Henry van den Bedem
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - Dana Weekes
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Program on Bioinformatics and Systems Biology, Sanford–Burnham Medical Research Institute, La Jolla, CA, USA
| | - Qingping Xu
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - Keith O. Hodgson
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Photon Science, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | - John Wooley
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Center for Research in Biological Systems, University of California, San Diego, La Jolla, CA, USA
| | - Marc-André Elsliger
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Ashley M. Deacon
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
| | - Adam Godzik
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Center for Research in Biological Systems, University of California, San Diego, La Jolla, CA, USA
- Program on Bioinformatics and Systems Biology, Sanford–Burnham Medical Research Institute, La Jolla, CA, USA
| | - Scott A. Lesley
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Protein Sciences Department, Genomics Institute of the Novartis Research Foundation, San Diego, CA, USA
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Ian A. Wilson
- Joint Center for Structural Genomics, http://www.jcsg.org, USA
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA, USA
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15
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Graindorge M, Giustini C, Jacomin AC, Kraut A, Curien G, Matringe M. Identification of a plant gene encoding glutamate/aspartate-prephenate aminotransferase: the last homeless enzyme of aromatic amino acids biosynthesis. FEBS Lett 2010; 584:4357-60. [PMID: 20883697 DOI: 10.1016/j.febslet.2010.09.037] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2010] [Revised: 09/20/2010] [Accepted: 09/22/2010] [Indexed: 10/19/2022]
Abstract
In all organisms synthesising phenylalanine and/or tyrosine via arogenate, a prephenate aminotransferase is required for the transamination of prephenate into arogenate. The identity of the gene encoding this enzyme in the organisms where this activity occurs is still unknown. Glutamate/aspartate-prephenate aminotransferase (PAT) is thus the last homeless enzyme in the aromatic amino acids pathway. We report on the purification, mass spectrometry identification and biochemical characterization of Arabidopsis thaliana prephenate aminotransferase. Our data revealed that this activity is housed by the prokaryotic-type plastidic aspartate aminotransferase (At2g22250). This represents the first identification of a gene encoding PAT.
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16
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Cohesion group approach for evolutionary analysis of TyrA, a protein family with wide-ranging substrate specificities. Microbiol Mol Biol Rev 2008; 72:13-53, table of contents. [PMID: 18322033 DOI: 10.1128/mmbr.00026-07] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Many enzymes and other proteins are difficult subjects for bioinformatic analysis because they exhibit variant catalytic, structural, regulatory, and fusion mode features within a protein family whose sequences are not highly conserved. However, such features reflect dynamic and interesting scenarios of evolutionary importance. The value of experimental data obtained from individual organisms is instantly magnified to the extent that given features of the experimental organism can be projected upon related organisms. But how can one decide how far along the similarity scale it is reasonable to go before such inferences become doubtful? How can a credible picture of evolutionary events be deduced within the vertical trace of inheritance in combination with intervening events of lateral gene transfer (LGT)? We present a comprehensive analysis of a dehydrogenase protein family (TyrA) as a prototype example of how these goals can be accomplished through the use of cohesion group analysis. With this approach, the full collection of homologs is sorted into groups by a method that eliminates bias caused by an uneven representation of sequences from organisms whose phylogenetic spacing is not optimal. Each sufficiently populated cohesion group is phylogenetically coherent and defined by an overall congruence with a distinct section of the 16S rRNA gene tree. Exceptions that occasionally are found implicate a clearly defined LGT scenario whereby the recipient lineage is apparent and the donor lineage of the gene transferred is localized to those organisms that define the cohesion group. Systematic procedures to manage and organize otherwise overwhelming amounts of data are demonstrated.
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17
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Metabolic engineering of Escherichia coli for L-tyrosine production by expression of genes coding for the chorismate mutase domain of the native chorismate mutase-prephenate dehydratase and a cyclohexadienyl dehydrogenase from Zymomonas mobilis. Appl Environ Microbiol 2008; 74:3284-90. [PMID: 18344329 DOI: 10.1128/aem.02456-07] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The expression of the feedback inhibition-insensitive enzyme cyclohexadienyl dehydrogenase (TyrC) from Zymomonas mobilis and the chorismate mutase domain from native chorismate mutase-prephenate dehydratase (PheA(CM)) from Escherichia coli was compared to the expression of native feedback inhibition-sensitive chorismate mutase-prephenate dehydrogenase (CM-TyrA(p)) with regard to the capacity to produce l-tyrosine in E. coli strains modified to increase the carbon flow to chorismate. Shake flask experiments showed that TyrC increased the yield of l-tyrosine from glucose (Y(l-Tyr/Glc)) by 6.8-fold compared to the yield obtained with CM-TyrA(p). In bioreactor experiments, a strain expressing both TyrC and PheA(CM) produced 3 g/liter of l-tyrosine with a Y(l-Tyr/Glc) of 66 mg/g. These values are 46 and 48% higher than the values for a strain expressing only TyrC. The results show that the feedback inhibition-insensitive enzymes can be employed for strain development as part of a metabolic engineering strategy for l-tyrosine production.
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18
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Kleeb AC, Edalat MH, Gamper M, Haugstetter J, Giger L, Neuenschwander M, Kast P, Hilvert D. Metabolic engineering of a genetic selection system with tunable stringency. Proc Natl Acad Sci U S A 2007; 104:13907-12. [PMID: 17715291 PMCID: PMC1955800 DOI: 10.1073/pnas.0705379104] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The biosynthesis of small molecules can be fine-tuned by (re)engineering metabolic flux within cells. We have adapted this approach to optimize an in vivo selection system for the conversion of prephenate to phenylpyruvate, a key step in the production of the essential aromatic amino acid phenylalanine. Careful control of prephenate concentration in a bacterial host lacking prephenate dehydratase, achieved through provision of a regulable enzyme that diverts it down a parallel biosynthetic pathway, provides the means to systematically increase selection pressure on replacements of the missing catalyst. Successful differentiation of dehydratases whose activities vary over a >50,000-fold range and the isolation of mechanistically informative prephenate dehydratase variants from large protein libraries illustrate the potential of the engineered selection strain for characterizing and evolving enzymes. Our approach complements other common methods for adjusting selection pressure and should be generally applicable to any selection system that is based on the conversion of an endogenous metabolite.
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Affiliation(s)
- Andreas C. Kleeb
- Laboratory of Organic Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
| | | | - Marianne Gamper
- Laboratory of Organic Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
| | | | - Lars Giger
- Laboratory of Organic Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
| | | | - Peter Kast
- Laboratory of Organic Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Donald Hilvert
- Laboratory of Organic Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland
- *To whom correspondence should be addressed. E-mail:
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19
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Legrand P, Dumas R, Seux M, Rippert P, Ravelli R, Ferrer JL, Matringe M. Biochemical characterization and crystal structure of Synechocystis arogenate dehydrogenase provide insights into catalytic reaction. Structure 2006; 14:767-76. [PMID: 16615917 DOI: 10.1016/j.str.2006.01.006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Revised: 01/10/2006] [Accepted: 01/17/2006] [Indexed: 10/24/2022]
Abstract
The extreme diversity in substrate specificity, and in the regulation mechanism of arogenate/prephenate dehydrogenase enzymes in nature, makes a comparative structural study of these enzymes of great interest. We report here on the biochemical and structural characterization of arogenate dehydrogenase from Synechocystis sp. (TyrAsy). This work paves the way for the understanding of the structural determinants leading to diversity in substrate specificity, and of the regulation mechanisms of arogenate/prephenate dehydrogenases. The overall structure of TyrAsy in complex with NADP was refined to 1.6 A. The asymmetric unit contains two TyrAsy homodimers, with each monomer consisting of a nucleotide binding N-terminal domain and a particularly unique alpha-helical C-terminal dimerization domain. The substrate arogenate was modeled into the active site. The model of the ternary complex enzyme-NADP-arogenate nicely reveals at the atomic level the concerted mechanism of the arogenate/prephenate dehydrogenase reaction.
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Affiliation(s)
- Pierre Legrand
- Institut de Biologie Structurale Jean-Pierre Ebel, Centre National de la Recherche Scientifique, Université Joseph Fourier, Laboratoire de Cristallographie et Cristallogenèse des Protéines/Groupe Synchrotron, 38027 Grenoble cedex 1, France
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20
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Bonvin J, Aponte RA, Marcantonio M, Singh S, Christendat D, Turnbull JL. Biochemical characterization of prephenate dehydrogenase from the hyperthermophilic bacterium Aquifex aeolicus. Protein Sci 2006; 15:1417-32. [PMID: 16731976 PMCID: PMC2265095 DOI: 10.1110/ps.051942206] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2005] [Revised: 03/01/2006] [Accepted: 03/01/2006] [Indexed: 10/24/2022]
Abstract
A monofunctional prephenate dehydrogenase (PD) from Aquifex aeolicus was expressed as a His-tagged protein in Escherichia coli and was purified by nickel affinity chromatography allowing the first biochemical and biophysical characterization of a thermostable PD. A. aeolicus PD is susceptible to proteolysis. In this report, the properties of the full-length PD are compared with one of these products, an N-terminally truncated protein variant (Delta19PD) also expressed recombinantly in E. coli. Both forms are dimeric and show maximum activity at 95 degrees C or higher. Delta19PD is more sensitive to temperature effects yielding a half-life of 55 min at 95 degrees C versus 2 h for PD, and values of kcat and Km for prephenate, which are twice those determined for PD at 80 degrees C. Low concentrations of guanidine-HCl activate enzyme activity, but at higher concentrations activity is lost concomitant with a multi-state pathway of denaturation that proceeds through unfolding of the dimer, oligomerization, then unfolding of monomers. Measurements of steady-state fluorescence intensity and its quenching by acrylamide in the presence of Gdn-HCl suggest that, of the two tryptophan residues per monomer, one is buried in a hydrophobic pocket and does not become solvent exposed until the protein unfolds, while the less buried tryptophan is at the active site. Tyrosine is a feedback inhibitor of PD activity over a wide temperature range and enhances the cooperativity between subunits in the binding of prephenate. Properties of this thermostable PD are compared and contrasted with those of E. coli chorismate mutase-prephenate dehydrogenase and other mesophilic homologs.
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Affiliation(s)
- Julie Bonvin
- Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec H4B 1R6, Canada
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21
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Song J, Bonner CA, Wolinsky M, Jensen RA. The TyrA family of aromatic-pathway dehydrogenases in phylogenetic context. BMC Biol 2005; 3:13. [PMID: 15888209 PMCID: PMC1173090 DOI: 10.1186/1741-7007-3-13] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2005] [Accepted: 05/12/2005] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The TyrA protein family includes members that catalyze two dehydrogenase reactions in distinct pathways leading to L-tyrosine and a third reaction that is not part of tyrosine biosynthesis. Family members share a catalytic core region of about 30 kDa, where inhibitors operate competitively by acting as substrate mimics. This protein family typifies many that are challenging for bioinformatic analysis because of relatively modest sequence conservation and small size. RESULTS Phylogenetic relationships of TyrA domains were evaluated in the context of combinatorial patterns of specificity for the two substrates, as well as the presence or absence of a variety of fusions. An interactive tool is provided for prediction of substrate specificity. Interactive alignments for a suite of catalytic-core TyrA domains of differing specificity are also provided to facilitate phylogenetic analysis. tyrA membership in apparent operons (or supraoperons) was examined, and patterns of conserved synteny in relationship to organismal positions on the 16S rRNA tree were ascertained for members of the domain Bacteria. A number of aromatic-pathway genes (hisHb, aroF, aroQ) have fused with tyrA, and it must be more than coincidental that the free-standing counterparts of all of the latter fused genes exhibit a distinct trace of syntenic association. CONCLUSION We propose that the ancestral TyrA dehydrogenase had broad specificity for both the cyclohexadienyl and pyridine nucleotide substrates. Indeed, TyrA proteins of this type persist today, but it is also common to find instances of narrowed substrate specificities, as well as of acquisition via gene fusion of additional catalytic domains or regulatory domains. In some clades a qualitative change associated with either narrowed substrate specificity or gene fusion has produced an evolutionary "jump" in the vertical genealogy of TyrA homologs. The evolutionary history of gene organizations that include tyrA can be deduced in genome assemblages of sufficiently close relatives, the most fruitful opportunities currently being in the Proteobacteria. The evolution of TyrA proteins within the broader context of how their regulation evolved and to what extent TyrA co-evolved with other genes as common members of aromatic-pathway regulons is now feasible as an emerging topic of ongoing inquiry.
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Affiliation(s)
- Jian Song
- Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA
| | - Carol A Bonner
- Emerson Hall, University of Florida, P.O. Box 14425, Gainesville, Florida, 32604-2425, USA
| | - Murray Wolinsky
- Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA
| | - Roy A Jensen
- Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA
- Emerson Hall, University of Florida, P.O. Box 14425, Gainesville, Florida, 32604-2425, USA
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22
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Bonner C, Jensen R, Gander J, Keyhani N. A core catalytic domain of the TyrA protein family: arogenate dehydrogenase from Synechocystis. Biochem J 2005; 382:279-91. [PMID: 15171683 PMCID: PMC1133941 DOI: 10.1042/bj20031809] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2003] [Revised: 05/11/2004] [Accepted: 06/01/2004] [Indexed: 11/17/2022]
Abstract
The TyrA protein family includes prephenate dehydrogenases, cyclohexadienyl dehydrogenases and TyrA(a)s (arogenate dehydrogenases). tyrA(a) from Synechocystis sp. PCC 6803, encoding a 30 kDa TyrA(a) protein, was cloned into an overexpression vector in Escherichia coli. TyrA(a) was then purified to apparent homogeneity and characterized. This protein is a model structure for a catalytic core domain in the TyrA superfamily, uncomplicated by allosteric or fused domains. Competitive inhibitors acting at the catalytic core of TyrA proteins are analogues of any accepted cyclohexadienyl substrate. The homodimeric enzyme was specific for L-arogenate (K(m)=331 microM) and NADP+ (K(m)=38 microM), being unable to substitute prephenate or NAD+ respectively. L-Tyrosine was a potent inhibitor of the enzyme (K(i)=70 microM). NADPH had no detectable ability to inhibit the reaction. Although the mechanism is probably steady-state random order, properties of 2',5'-ADP as an inhibitor suggest a high preference for L-arogenate binding first. Comparative enzymology established that both of the arogenate-pathway enzymes, prephenate aminotransferase and TyrA(a), were present in many diverse cyanobacteria and in a variety of eukaryotic red and green algae.
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Affiliation(s)
- Carol A. Bonner
- *Department of Microbiology and Cell Science, Bldg 981, PO Box 110700, University of Florida, Gainesville, FL 32611, U.S.A
| | - Roy A. Jensen
- *Department of Microbiology and Cell Science, Bldg 981, PO Box 110700, University of Florida, Gainesville, FL 32611, U.S.A
- †Biosciences Division, Los Alamos National Laboratory, Los Alamos, NM 87544, U.S.A
- ‡Department of Chemistry, City College of New York, New York, NY 10031, U.S.A
| | - John E. Gander
- *Department of Microbiology and Cell Science, Bldg 981, PO Box 110700, University of Florida, Gainesville, FL 32611, U.S.A
| | - Nemat O. Keyhani
- *Department of Microbiology and Cell Science, Bldg 981, PO Box 110700, University of Florida, Gainesville, FL 32611, U.S.A
- To whom correspondence should be addressed (email )
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23
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Rippert P, Matringe M. Purification and kinetic analysis of the two recombinant arogenate dehydrogenase isoforms of Arabidopsis thaliana. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:4753-61. [PMID: 12354106 DOI: 10.1046/j.1432-1033.2002.03172.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The present study reports the first purification and kinetic characterization of two plant arogenate dehydrogenases (EC 1.3.1.43), an enzyme that catalyses the oxidative decarboxylation of arogenate into tyrosine in presence of NADP. The two Arabidopsis thaliana arogenate dehydrogenases TyrAAT1 and TyrAAT2 were overproduced in Escherichia coli and purified to homogeneity. Biochemical comparison of the two forms revealed that at low substrate concentration TyrAAT1 is four times more efficient in catalyzing the arogenate dehydrogenase reaction than TyrAAT2. Moreover, TyrAAT2 presents a weak prephenate dehydrogenase activity whereas TyrAAT1 does not. The mechanism of the dehydrogenase reaction catalyzed by these two forms has been investigated using steady-state kinetics. For both enzymes, steady-state velocity patterns are consistent with a rapid equilibrium, random mechanism in which two dead-end complexes, E-NADPH-arogenate and E-NADP-tyrosine, are formed.
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Affiliation(s)
- Pascal Rippert
- Laboratoire Mixte CNRS/INRA/Bayer CropScience (UMR 1932), Lyon, France
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24
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Xie G, Bonner CA, Jensen RA. Cyclohexadienyl dehydrogenase from Pseudomonas stutzeri exemplifies a widespread type of tyrosine-pathway dehydrogenase in the TyrA protein family. Comp Biochem Physiol C Toxicol Pharmacol 2000; 125:65-83. [PMID: 11790331 DOI: 10.1016/s0742-8413(99)00090-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The uni-domain cyclohexadienyl dehydrogenases are able to use the alternative intermediates of tyrosine biosynthesis, prephenate or L-arogenate, as substrates. Members of this TyrA protein family have been generally considered to fall into two classes: sensitive or insensitive to feedback inhibition by L-tyrosine. A gene (tyrA(c)) encoding a cyclohexadienyl dehydrogenase from Pseudomonas stutzeri JM300 was cloned, sequenced, and expressed at a high level in Escherichia coli. This is the first molecular-genetic and biochemical characterization of a purified protein representing the feedback-sensitive type of cyclohexadienyl dehydrogenase. The catalytic-efficiency constant k(cat)/K(m) for prephenate (7.0x10(7) M/s) was much better than that of L-arogenate (5.7x10(6) M/s). TyrA(c) was sensitive to feedback inhibition by either L-tyrosine or 4-hydroxyphenylpyruvate, competitively with respect to either prephenate or L-arogenate and non-competitively with respect to NAD(+). A variety of related compounds were tested as inhibitors, and the minimal inhibitor structure was found to require only the aromatic ring and a hydroxyl substituent. Analysis by multiple alignment was used to compare 17 protein sequences representing TyrA family members having catalytic domains that are independent or fused to other catalytic domains, that exhibit broad substrate specificity or narrow substrate specificity, and that possess or lack sensitivity to endproduct inhibitors. We propose that the entire TyrA protein family lacks a discrete allosteric domain and that inhibitors act competitively at the catalytic site of different family members which exhibit individuality in the range and extent of molecules recognized as substrate or inhibitor.
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Affiliation(s)
- G Xie
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611, USA
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Christendat D, Turnbull JL. Identifying groups involved in the binding of prephenate to prephenate dehydrogenase from Escherichia coli. Biochemistry 1999; 38:4782-93. [PMID: 10200166 DOI: 10.1021/bi982673o] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Site-directed mutagenesis was used to investigate the importance of Lys178, Arg286, and Arg294 in the binding of prephenate to the bifunctional enzyme chorismate mutase-prephenate dehydrogenase. From comparison of the kinetic parameters of wild-type enzyme and selected mutants, we conclude that only Arg294 interacts specifically with prephenate. The R294Q substitution reduces the enzyme's affinity for prephenate without affecting V/Et of the dehydrogenase reaction or the kinetic parameters of the mutase reaction. Arg294 likely interacts with the ring carboxylate at C-1 of prephenate since the dissociation constants for a series of inhibitors missing the ring carboxyl group were similar for wild-type and R294Q enzymes. The pH dependencies of log (V/KprephenateEt) and of pKi for hydroxyphenyllactate show that the wild-type dehydrogenase possesses a group with a pK of 8.8 that must be protonated for binding prephenate to the enzyme. None of the three conserved residues is this group since its titration is observed in the V/KprephenateEt profiles for the mutants K178Q, R286A, and R294Q. This group is also seen in the pH-rate profiles of the binding of two substrate analogues, hydroxyphenyllactate and deoxoprephenate. Their only common structural feature at C-1 is the side chain carboxylate, indicating that the protonated residue (pK 8.8) must interact with prephenate's side chain carboxylate. Gdn-HCl-induced denaturation was conducted on wild-type and selected mutant proteins. Unfolding of the wild-type enzyme proceeds through a partially unfolded dimer which dissociates into unfolded monomers. The order of stability is wild-type = R294Q > K178Q > R286A > K178R. The least unstable mutants have reduced mutase and dehydrogenase activities.
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Affiliation(s)
- D Christendat
- Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec, H3G 1M8, Canada
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Christendat D, Saridakis VC, Turnbull JL. Use of site-directed mutagenesis to identify residues specific for each reaction catalyzed by chorismate mutase-prephenate dehydrogenase from Escherichia coli. Biochemistry 1998; 37:15703-12. [PMID: 9843375 DOI: 10.1021/bi981412b] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Site-directed mutagenesis was performed on the bifunctional enzyme chorismate mutase-prephenate dehydrogenase in order to identify groups important for each of the two reactions. We selected two residues for mutagenesis, Lys37 and His131, identified previously by differential peptide mapping to be essential for activity [Christendat, D., and Turnbull, J. (1996) Biochemistry 35, 4468-4479]. Kinetic studies reveal that K37Q exhibits no mutase activity while retaining wild-type dehydrogenase activity, verifying that Lys37 plays a key role in the mutase. By contrast His131 is not critical for the dehydrogenase; H131A is a reasonably efficient catalyst exhibiting 10% dehydrogenase and 30% mutase activity compared to the wild-type enzyme. Chemical modification of H131A by diethyl pyrocarbonate further inactivated the dehydrogenase, suggesting that a different histidine is now accessible to modification. To identify this group, the protein's remaining eight histidines were changed to alanine or asparagine. A single substitution, H197N, decreased the dehydrogenase activity by 5 orders of magnitude while full mutase activity was retained. In H197N, the Michaelis constants for prephenate and NAD+ and the mutant's elution profile from Sepharose-AMP were similar to those of wild-type enzyme, indicating that catalysis rather than substrate binding is altered. Log V for the dehydrogenase reaction catalyzed by H197N is pH-independent and is in contrast to wild-type enzyme, which shows a decrease in activity at low pH and pK of about 6.5. We conclude that His197 is an essential catalytic residue in the dehydrogenase reaction.
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Affiliation(s)
- D Christendat
- Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada
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27
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Gu W, Zhao G, Eddy C, Jensen RA. Imidazole acetol phosphate aminotransferase in Zymomonas mobilis: molecular genetic, biochemical, and evolutionary analyses. J Bacteriol 1995; 177:1576-84. [PMID: 7883715 PMCID: PMC176775 DOI: 10.1128/jb.177.6.1576-1584.1995] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
hisH encodes imidazole acetol phosphate (IAP) aminotransferase in Zymomonas mobilis and is located immediately upstream of tyrC, a gene which codes for cyclohexadienyl dehydrogenase. A plasmid containing hisH was able to complement an Escherichia coli histidine auxotroph which lacked the homologous aminotransferase. DNA sequencing of hisH revealed an open reading frame of 1,110 bp, encoding a protein of 40,631 Da. The cloned hisH product was purified from E. coli and estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to have a molecular mass of 40,000 Da. Since the native enzyme had a molecular mass of 85,000 Da as determined by gel filtration, the active enzyme species must be a homodimer. The purified enzyme was able to transaminate aromatic amino acids and histidine in addition to histidinol phosphate. The existence of a single protein having broad substrate specificity was consistent with the constant ratio of activities obtained with different substrates following a variety of physical treatments (such as freeze-thaw, temperature inactivation, and manipulation of pyridoxal 5'-phosphate content). The purified enzyme did not require addition of pyridoxal 5'-phosphate, but dependence upon this cofactor was demonstrated following resolution of the enzyme and cofactor by hydroxylamine treatment. Kinetic data showed the classic ping-pong mechanism expected for aminotransferases. Km values of 0.17, 3.39, and 43.48 mM for histidinol phosphate, tyrosine, and phenylalanine were obtained. The gene structure around hisH-tyrC suggested an operon organization. The hisH-tyrC cluster in Z. mobilis is reminiscent of the hisH-tyrA component of a complex operon in Bacillus subtilis, which includes the tryptophan operon and aroE. Multiple alignment of all aminotransferase sequences available in the database showed that within the class I superfamily of aminotransferases, IAP aminotransferases (family I beta) are closer to the I gamma family (e.g., rat tyrosine aminotransferase) than to the I alpha family (e.g., rat aspartate aminotransferase or E. coli AspC). Signature motifs which distinguish the IAP aminotransferase family were identified in the region of the active-site lysine and in the region of the interdomain interface.
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Affiliation(s)
- W Gu
- Department of Microbiology and Cell Science, University of Florida, Gainesville 32611
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Griffin HG, Gasson MJ. Genetic aspects of aromatic amino acid biosynthesis in Lactococcus lactis. MOLECULAR & GENERAL GENETICS : MGG 1995; 246:119-27. [PMID: 7823907 DOI: 10.1007/bf00290140] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Polymerase chain reaction (PCR) primers designed from a multiple alignment of predicted amino acid sequences from bacterial aroA genes were used to amplify a fragment of Lactococcus lactis DNA. An 8 kb fragment was then cloned from a lambda library and the DNA sequence of a 4.4 kb region determined. This region was found to contain the genes tyrA, aroA, aroK, and pheA, which are involved in aromatic amino acid biosynthesis and folate metabolism. TyrA has been shown to be secreted and AroK also has a signal sequence, suggesting that these proteins have a secondary function, possibly in the transport of amino acids. The aroA gene from L. lactis has been shown to complement an E. coli mutant strain deficient in this gene. The arrangement of genes involved in aromatic amino acid biosynthesis in L. lactis appears to differ from that in other organisms.
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Affiliation(s)
- H G Griffin
- Institute of Food Research, Norwich Research Park, Colney, UK
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Xia T, Song J, Zhao G, Aldrich H, Jensen RA. The aroQ-encoded monofunctional chorismate mutase (CM-F) protein is a periplasmic enzyme in Erwinia herbicola. J Bacteriol 1993; 175:4729-37. [PMID: 8335631 PMCID: PMC204924 DOI: 10.1128/jb.175.15.4729-4737.1993] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Enteric bacteria possess two species of chorismate mutase which exist as catalytic domains on the amino termini of the bifunctional PheA and TyrA proteins. In addition, some of these organisms possess a third chorismate mutase, CM-F, which exists as a small monofunctional protein. The CM-F gene (denoted aroQ) from Erwinia herbicola was cloned and sequenced for the first time. A strategy for selection by functional complementation in a chorismate mutase-free Escherichia coli background was devised by using a recombinant plasmid derivative of pUC18 carrying a Zymomonas mobilis tyrC insert which encodes cyclohexadienyl dehydrogenase. The aroQ gene is 543 bp in length, predicting a 181-residue protein product having a calculated molecular mass of 20,299 Da. The E. herbicola aroQ promoter is recognized by E. coli, and a putative sigma-70 promoter region was identified. N-terminal amino acid sequencing of the purified CM-F protein indicated cleavage of a 20-residue signal peptide. This was consistent with the monomeric molecular mass determined for the enzyme of about 18,000 Da. The native enzyme is a homodimer. The implied translocation of CM-F was confirmed by osmotic shock experiments which demonstrated a periplasmic location. Immunogold electron microscopy indicated a polar localization within the periplasm. Polyclonal antibody raised against E. herbicola CM-F did not cross-react with the CM-F protein from the closely related Serratia rubidaea, as well as from a number of other gram-negative bacteria. Furthermore, when the E. herbicola aroQ gene was used as a probe in Southern blot hybridizations with EcroRI digests of chromosomal DNA from S. rubidaea and other enteric organisms, no hybridization was detected at low stringency. Thus, the aroQ gene appears to be unusually divergent among closely related organisms. The deduced CM-F amino acid sequence did not exhibit compelling evidence for homology with the monofunctional chorismate mutase protein of Bacillus subtilis.
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Affiliation(s)
- T Xia
- Department of Microbiology and Cell Science, University of Florida, Gainesville 32611-0100
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