1
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Duangsri C, Salminen TA, Alix M, Kaewmongkol S, Akrimajirachoote N, Khetkorn W, Jittapalapong S, Mäenpää P, Incharoensakdi A, Raksajit W. Characterization and Homology Modeling of Catalytically Active Recombinant PhaC Ap Protein from Arthrospira platensis. BIOLOGY 2023; 12:biology12050751. [PMID: 37237563 DOI: 10.3390/biology12050751] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Revised: 04/30/2023] [Accepted: 05/17/2023] [Indexed: 05/28/2023]
Abstract
Polyhydroxybutyrate (PHB) is a biocompatible and biodegradable polymer that has the potential to replace fossil-derived polymers. The enzymes involved in the biosynthesis of PHB are β-ketothiolase (PhaA), acetoacetyl-CoA reductase (PhaB), and PHA synthase (PhaC). PhaC in Arthrospira platensis is the key enzyme for PHB production. In this study, the recombinant E. cloni®10G cells harboring A. platensis phaC (rPhaCAp) was constructed. The overexpressed and purified rPhaCAp with a predicted molecular mass of 69 kDa exhibited Vmax, Km, and kcat values of 24.5 ± 2 μmol/min/mg, 31.3 ± 2 µM and 412.7 ± 2 1/s, respectively. The catalytically active rPhaCAp was a homodimer. The three-dimensional structural model for the asymmetric PhaCAp homodimer was constructed based on Chromobacterium sp. USM2 PhaC (PhaCCs). The obtained model of PhaCAp revealed that the overall fold of one monomer was in the closed, catalytically inactive conformation whereas the other monomer was in the catalytically active, open conformation. In the active conformation, the catalytic triad residues (Cys151-Asp310-His339) were involved in the binding of substrate 3HB-CoA and the CAP domain of PhaCAp involved in the dimerization.
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Affiliation(s)
- Chanchanok Duangsri
- Program of Animal Health Technology, Faculty of Veterinary Technology, Kasetsart University, Bangkok 10900, Thailand
| | - Tiina A Salminen
- Structural Bioinformatics Laboratory and InFLAMES Research Flagship Center, Biochemistry, Faculty of Science and Engineering, Åbo Akademi University, 20520 Turku, Finland
| | - Marion Alix
- Structural Bioinformatics Laboratory and InFLAMES Research Flagship Center, Biochemistry, Faculty of Science and Engineering, Åbo Akademi University, 20520 Turku, Finland
| | - Sarawan Kaewmongkol
- Program of Animal Health Technology, Faculty of Veterinary Technology, Kasetsart University, Bangkok 10900, Thailand
| | | | - Wanthanee Khetkorn
- Division of Biology, Faculty of Science and Technology, Rajamangala University of Technology Thanyaburi (RMUTT), Thanyaburi, Pathumthani 12110, Thailand
| | - Sathaporn Jittapalapong
- Program of Animal Health Technology, Faculty of Veterinary Technology, Kasetsart University, Bangkok 10900, Thailand
| | - Pirkko Mäenpää
- Faculty of Technology, University of Turku, 20014 Turku, Finland
| | - Aran Incharoensakdi
- Laboratory of Cyanobacterial Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
- Academy of Science, Royal Society of Thailand, Bangkok 10300, Thailand
| | - Wuttinun Raksajit
- Program of Animal Health Technology, Faculty of Veterinary Technology, Kasetsart University, Bangkok 10900, Thailand
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2
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Lai J, Huang H, Lin M, Xu Y, Li X, Sun B. Enzyme catalyzes ester bond synthesis and hydrolysis: The key step for sustainable usage of plastics. Front Microbiol 2023; 13:1113705. [PMID: 36713200 PMCID: PMC9878459 DOI: 10.3389/fmicb.2022.1113705] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Accepted: 12/29/2022] [Indexed: 01/15/2023] Open
Abstract
Petro-plastic wastes cause serious environmental contamination that require effective solutions. Developing alternatives to petro-plastics and exploring feasible degrading methods are two solving routes. Bio-plastics like polyhydroxyalkanoates (PHAs), polylactic acid (PLA), polycaprolactone (PCL), poly (butylene succinate) (PBS), poly (ethylene furanoate) s (PEFs) and poly (ethylene succinate) (PES) have emerged as promising alternatives. Meanwhile, biodegradation plays important roles in recycling plastics (e.g., bio-plastics PHAs, PLA, PCL, PBS, PEFs and PES) and petro-plastics poly (ethylene terephthalate) (PET) and plasticizers in plastics (e.g., phthalate esters, PAEs). All these bio- and petro-materials show structure similarity by connecting monomers through ester bond. Thus, this review focused on bio-plastics and summarized the sequences and structures of the microbial enzymes catalyzing ester-bond synthesis. Most of these synthetic enzymes belonged to α/β-hydrolases with conserved serine catalytic active site and catalyzed the polymerization of monomers by forming ester bond. For enzymatic plastic degradation, enzymes about PHAs, PBS, PCL, PEFs, PES and PET were discussed, and most of the enzymes also belonged to the α/β hydrolases with a catalytic active residue serine, and nucleophilically attacked the ester bond of substrate to generate the cleavage of plastic backbone. Enzymes hydrolysis of the representative plasticizer PAEs were divided into three types (I, II, and III). Type I enzymes hydrolyzed only one ester-bond of PAEs, type II enzymes catalyzed the ester-bond of mono-ester phthalates, and type III enzymes hydrolyzed di-ester bonds of PAEs. Divergences of catalytic mechanisms among these enzymes were still unclear. This review provided references for producing bio-plastics, and degrading or recycling of bio- and petro-plastics from an enzymatic point of view.
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Affiliation(s)
- Jinghui Lai
- Key Laboratory of Brewing Microbiology and Enzymatic Molecular Engineering of China General Chamber of Commence, Beijing Technology and Business University, Beijing, China
| | - Huiqin Huang
- Key Laboratory of Brewing Microbiology and Enzymatic Molecular Engineering of China General Chamber of Commence, Beijing Technology and Business University, Beijing, China
| | - Mengwei Lin
- Key Laboratory of Brewing Microbiology and Enzymatic Molecular Engineering of China General Chamber of Commence, Beijing Technology and Business University, Beijing, China
| | - Youqiang Xu
- Key Laboratory of Brewing Microbiology and Enzymatic Molecular Engineering of China General Chamber of Commence, Beijing Technology and Business University, Beijing, China
| | - Xiuting Li
- Key Laboratory of Brewing Microbiology and Enzymatic Molecular Engineering of China General Chamber of Commence, Beijing Technology and Business University, Beijing, China
- Key Laboratory of Brewing Molecular Engineering of China Light Industry, Beijing Technology and Business University, Beijing, China
| | - Baoguo Sun
- Key Laboratory of Brewing Microbiology and Enzymatic Molecular Engineering of China General Chamber of Commence, Beijing Technology and Business University, Beijing, China
- Key Laboratory of Brewing Molecular Engineering of China Light Industry, Beijing Technology and Business University, Beijing, China
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3
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Chek MF, Kim SY, Mori T, Tan HT, Sudesh K, Hakoshima T. Asymmetric Open-Closed Dimer Mechanism of Polyhydroxyalkanoate Synthase PhaC. iScience 2020; 23:101084. [PMID: 32388399 PMCID: PMC7214940 DOI: 10.1016/j.isci.2020.101084] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 04/01/2020] [Accepted: 04/15/2020] [Indexed: 12/15/2022] Open
Abstract
Biodegradable polyester polyhydroxyalkanoate (PHA) is a promising bioplastic material for industrial use as a replacement for petroleum-based plastics. PHA synthase PhaC forms an active dimer to polymerize acyl moieties from the substrate acyl-coenzyme A (CoA) into PHA polymers. Here we present the crystal structure of the catalytic domain of PhaC from Chromobacterium sp. USM2, bound to CoA. The structure reveals an asymmetric dimer, in which one protomer adopts an open conformation bound to CoA, whereas the other adopts a closed conformation in a CoA-free form. The open conformation is stabilized by the asymmetric dimerization and enables PhaC to accommodate CoA and also to create the product egress path. The bound CoA molecule has its β-mercaptoethanolamine moiety extended into the active site with the terminal SH group close to active center Cys291, enabling formation of the reaction intermediate by acylation of Cys291. Crystal structure of PhaCCs-CAT bound to coenzyme A A unique asymmetric open-closed dimer Restructuring of the CAP subdomain provides a cleft toward the active site The cleft enables the substrate entry and the product egress
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Affiliation(s)
- Min Fey Chek
- Structural Biology Laboratory, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
| | - Sun-Yong Kim
- Structural Biology Laboratory, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
| | - Tomoyuki Mori
- Structural Biology Laboratory, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
| | - Hua Tiang Tan
- School of Biological Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia
| | - Kumar Sudesh
- School of Biological Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia
| | - Toshio Hakoshima
- Structural Biology Laboratory, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.
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4
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Sanhueza C, Acevedo F, Rocha S, Villegas P, Seeger M, Navia R. Polyhydroxyalkanoates as biomaterial for electrospun scaffolds. Int J Biol Macromol 2019; 124:102-110. [DOI: 10.1016/j.ijbiomac.2018.11.068] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Revised: 10/24/2018] [Accepted: 11/12/2018] [Indexed: 01/15/2023]
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5
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Chek MF, Hiroe A, Hakoshima T, Sudesh K, Taguchi S. PHA synthase (PhaC): interpreting the functions of bioplastic-producing enzyme from a structural perspective. Appl Microbiol Biotechnol 2018; 103:1131-1141. [DOI: 10.1007/s00253-018-9538-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 11/20/2018] [Accepted: 11/22/2018] [Indexed: 02/07/2023]
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6
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Sagong HY, Son HF, Choi SY, Lee SY, Kim KJ. Structural Insights into Polyhydroxyalkanoates Biosynthesis. Trends Biochem Sci 2018; 43:790-805. [PMID: 30139647 DOI: 10.1016/j.tibs.2018.08.005] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Revised: 07/27/2018] [Accepted: 08/04/2018] [Indexed: 12/25/2022]
Abstract
Polyhydroxyalkanoates (PHAs) are diverse biopolyesters produced by numerous microorganisms and have attracted much attention as a substitute for petroleum-based polymers. Despite several decades of study, the detailed molecular mechanisms of PHA biosynthesis have remained unknown due to the lack of structural information on the key PHA biosynthetic enzyme PHA synthase. The recently determined crystal structure of PHA synthase, together with the structures of acetyl-coenzyme A (CoA) acetyltransferase and reductase, have changed this situation. Structural and biochemical studies provided important clues for the molecular mechanisms of each enzyme as well as the overall mechanism of PHA biosynthesis from acetyl-CoA. This new information and knowledge is expected to facilitate production of designed novel PHAs and also enhanced production of PHAs.
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Affiliation(s)
- Hye-Young Sagong
- School of Life Sciences, KNU Creative BioResearch Group, Kyungpook National University, Daegu 41566, Republic of Korea; KNU Institute for Microorganisms, Kyungpook National University, Daegu 41566, Republic of Korea
| | - Hyeoncheol Francis Son
- School of Life Sciences, KNU Creative BioResearch Group, Kyungpook National University, Daegu 41566, Republic of Korea; KNU Institute for Microorganisms, Kyungpook National University, Daegu 41566, Republic of Korea
| | - So Young Choi
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Plus Program), BioProcess Engineering Research Center, Center for Systems and Synthetic Biotechnology, and Institute for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
| | - Sang Yup Lee
- Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering (BK21 Plus Program), BioProcess Engineering Research Center, Center for Systems and Synthetic Biotechnology, and Institute for the BioCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.
| | - Kyung-Jin Kim
- School of Life Sciences, KNU Creative BioResearch Group, Kyungpook National University, Daegu 41566, Republic of Korea; KNU Institute for Microorganisms, Kyungpook National University, Daegu 41566, Republic of Korea.
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7
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Zou H, Shi M, Zhang T, Li L, Li L, Xian M. Natural and engineered polyhydroxyalkanoate (PHA) synthase: key enzyme in biopolyester production. Appl Microbiol Biotechnol 2017; 101:7417-7426. [DOI: 10.1007/s00253-017-8485-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 08/07/2017] [Accepted: 08/10/2017] [Indexed: 01/30/2023]
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8
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Higuchi-Takeuchi M, Motoda Y, Kigawa T, Numata K. Class I Polyhydroxyalkanoate Synthase from the Purple Photosynthetic Bacterium Rhodovulum sulfidophilum Predominantly Exists as a Functional Dimer in the Absence of a Substrate. ACS OMEGA 2017; 2:5071-5078. [PMID: 30023736 PMCID: PMC6044645 DOI: 10.1021/acsomega.7b00667] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 07/21/2017] [Indexed: 06/01/2023]
Abstract
Polyhydroxyalkanoates (PHAs) are a family of biopolyesters that accumulate as carbon and energy storage compounds in a variety of micro-organisms. The marine purple photosynthetic bacterium Rhodovulum sulfidophilum is capable of synthesizing PHA. In this study, we cloned a gene encoding a class I PHA synthase from R. sulfidophilum (phaCRs ) and synthesized PhaCRs using a cell-free protein expression system. The specific activity of PhaCRs increased linearly as the (R)-3-hydroxybutyryl-coenzyme A (3HB-CoA) concentration increased and never reached a plateau, even at 3.75 mM 3HB-CoA, suggesting that PhaCRs was not saturated because of low substrate affinity. Size exclusion chromatography and native polyacrylamide gel electrophoresis analyses revealed that PhaCRs exists predominantly as an active dimer even in the absence of 3HB-CoA, unlike previously characterized PhaCs. The linear relationship between the PhaCRs activity and 3HB-CoA concentrations could result from a low substrate affinity as well as the absence of a rate-limiting step during PHA polymerization because of the existence of predominantly active dimers.
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Affiliation(s)
- Mieko Higuchi-Takeuchi
- Enzyme Research
Team, Biomass Engineering Research Division, RIKEN Center for Sustainable Resource Science, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
| | - Yoko Motoda
- Enzyme Research
Team, Biomass Engineering Research Division, RIKEN Center for Sustainable Resource Science, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
| | - Takanori Kigawa
- Laboratory for Biomolecular Structure and
Dynamics, RIKEN Quantitative Biology Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Keiji Numata
- Enzyme Research
Team, Biomass Engineering Research Division, RIKEN Center for Sustainable Resource Science, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
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9
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Structure of polyhydroxyalkanoate (PHA) synthase PhaC from Chromobacterium sp. USM2, producing biodegradable plastics. Sci Rep 2017; 7:5312. [PMID: 28706283 PMCID: PMC5509742 DOI: 10.1038/s41598-017-05509-4] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Accepted: 06/05/2017] [Indexed: 11/08/2022] Open
Abstract
Polyhydroxyalkanoate (PHA) is a promising candidate for use as an alternative bioplastic to replace petroleum-based plastics. Our understanding of PHA synthase PhaC is poor due to the paucity of available three-dimensional structural information. Here we present a high-resolution crystal structure of the catalytic domain of PhaC from Chromobacterium sp. USM2, PhaC Cs -CAT. The structure shows that PhaC Cs -CAT forms an α/β hydrolase fold comprising α/β core and CAP subdomains. The active site containing Cys291, Asp447 and His477 is located at the bottom of the cavity, which is filled with water molecules and is covered by the partly disordered CAP subdomain. We designated our structure as the closed form, which is distinct from the recently reported catalytic domain from Cupriavidus necator (PhaC Cn -CAT). Structural comparison showed PhaC Cn -CAT adopting a partially open form maintaining a narrow substrate access channel to the active site, but no product egress. PhaC Cs -CAT forms a face-to-face dimer mediated by the CAP subdomains. This arrangement of the dimer is also distinct from that of the PhaC Cn -CAT dimer. These findings suggest that the CAP subdomain should undergo a conformational change during catalytic activity that involves rearrangement of the dimer to facilitate substrate entry and product formation and egress from the active site.
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10
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Wittenborn EC, Jost M, Wei Y, Stubbe J, Drennan CL. Structure of the Catalytic Domain of the Class I Polyhydroxybutyrate Synthase from Cupriavidus necator. J Biol Chem 2016; 291:25264-25277. [PMID: 27742839 DOI: 10.1074/jbc.m116.756833] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Revised: 10/11/2016] [Indexed: 11/06/2022] Open
Abstract
Polyhydroxybutyrate synthase (PhaC) catalyzes the polymerization of 3-(R)-hydroxybutyryl-coenzyme A as a means of carbon storage in many bacteria. The resulting polymers can be used to make biodegradable materials with properties similar to those of thermoplastics and are an environmentally friendly alternative to traditional petroleum-based plastics. A full biochemical and mechanistic understanding of this process has been hindered in part by a lack of structural information on PhaC. Here we present the first structure of the catalytic domain (residues 201-589) of the class I PhaC from Cupriavidus necator (formerly Ralstonia eutropha) to 1.80 Å resolution. We observe a symmetrical dimeric architecture in which the active site of each monomer is separated from the other by ∼33 Å across an extensive dimer interface, suggesting a mechanism in which polyhydroxybutyrate biosynthesis occurs at a single active site. The structure additionally highlights key side chain interactions within the active site that play likely roles in facilitating catalysis, leading to the proposal of a modified mechanistic scheme involving two distinct roles for the active site histidine. We also identify putative substrate entrance and product egress routes within the enzyme, which are discussed in the context of previously reported biochemical observations. Our structure lays a foundation for further biochemical and structural characterization of PhaC, which could assist in engineering efforts for the production of eco-friendly materials.
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Affiliation(s)
| | | | | | | | - Catherine L Drennan
- From the Departments of Chemistry, .,Biology, and.,Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
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11
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Jia K, Cao R, Hua DH, Li P. Study of Class I and Class III Polyhydroxyalkanoate (PHA) Synthases with Substrates Containing a Modified Side Chain. Biomacromolecules 2016; 17:1477-85. [PMID: 26974339 PMCID: PMC4862738 DOI: 10.1021/acs.biomac.6b00082] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Polyhydroxyalkanoates (PHAs) are carbon and energy storage polymers produced by a variety of microbial organisms under nutrient-limited conditions. They have been considered as an environmentally friendly alternative to oil-based plastics due to their renewability, versatility, and biodegradability. PHA synthase (PhaC) plays a central role in PHA biosynthesis, in which its activity and substrate specificity are major factors in determining the productivity and properties of the produced polymers. However, the effects of modifying the substrate side chain are not well understood because of the difficulty to accessing the desired analogues. In this report, a series of 3-(R)-hydroxyacyl coenzyme A (HACoA) analogues were synthesized and tested with class I synthases from Chromobacterium sp. USM2 (PhaCCs and A479S-PhaCCs) and Caulobacter crescentus (PhaCCc) as well as class III synthase from Allochromatium vinosum (PhaECAv). It was found that, while different PHA synthases displayed distinct preference with regard to the length of the alkyl side chains, they could withstand moderate side chain modifications such as terminal unsaturated bonds and the azide group. Specifically, the specific activity of PhaCCs toward propynyl analogue (HHxyCoA) was only 5-fold less than that toward the classical substrate HBCoA. The catalytic efficiency (kcat/Km) of PhaECAv toward azide analogue (HABCoA) was determined to be 2.86 × 10(5) M(-1) s(-1), which was 6.2% of the value of HBCoA (4.62 × 10(6) M(-1) s(-1)) measured in the presence of bovine serum albumin (BSA). These side chain modifications may be employed to introduce new material functions to PHAs as well as to study PHA biogenesis via click-chemistry, in which the latter remains unknown and is important for metabolic engineering to produce PHAs economically.
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Affiliation(s)
| | | | - Duy H. Hua
- Department of Chemistry, Kansas State University, Manhattan, Kansas, 66506, United States
| | - Ping Li
- Department of Chemistry, Kansas State University, Manhattan, Kansas, 66506, United States
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12
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Chen C, Cao R, Shrestha R, Ward C, Katz BB, Fischer CJ, Tomich JM, Li P. Trapping of intermediates with substrate analog HBOCoA in the polymerizations catalyzed by class III polyhydroxybutyrate (PHB) synthase from Allochromatium vinosum. ACS Chem Biol 2015; 10:1330-1339. [PMID: 25686368 DOI: 10.1021/cb5009958] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Polyhydroxybutyrate (PHB) synthases (PhaCs) catalyze the formation of biodegradable PHB polymers that are considered as an ideal alternative to petroleum-based plastics. To provide strong evidence for the preferred mechanistic model involving covalent and noncovalent intermediates, a substrate analog HBOCoA was synthesized chemoenzymatically. Substitution of sulfur in the native substrate HBCoA with an oxygen in HBOCoA enabled detection of (HB)nOCoA (n = 2-6) intermediates when the polymerization was catalyzed by wild-type (wt-)PhaECAv at 5.84 h(-1). This extremely slow rate is due to thermodynamically unfavorable steps that involve the formation of enzyme-bound PHB species (thioesters) from corresponding CoA oxoesters. Synthesized standards (HB)nOCoA (n = 2-3) were found to undergo both reacylation and hydrolysis catalyzed by the synthase. Distribution of the hydrolysis products highlights the importance of the penultimate ester group as previously suggested. Importantly, the reaction between primed synthase [(3)H]-sT-PhaECAv and HBOCoA yielded [(3)H]-sTet-O-CoA at a rate constant faster than 17.4 s(-1), which represents the first example that a substrate analog undergoes PHB chain elongation at a rate close to that of the native substrate (65.0 s(-1)). Therefore, for the first time with a wt-synthase, strong evidence was obtained to support our favored PHB chain elongation model.
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Affiliation(s)
| | | | | | - Christina Ward
- University of Saint Mary, Leavenworth, Kansas 66048, United States
| | | | - Christopher J. Fischer
- Department
of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, United States
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Buckley RM, Stubbe J. Chemistry with an artificial primer of polyhydroxybutyrate synthase suggests a mechanism for chain termination. Biochemistry 2015; 54:2117-25. [PMID: 25741756 PMCID: PMC4684083 DOI: 10.1021/bi501405b] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Polyhydroxybutyrate
(PHB) synthases (PhaCs) catalyze the conversion
of 3-(R)-hydroxybutyryl CoA (HBCoA) to PHB, which
is deposited as granules in the cytoplasm of microorganisms. The class
I PhaC from Caulobacter crescentus (PhaCCc) is a highly soluble protein with a turnover number of 75 s–1 and no lag phase in coenzyme A (CoA) release. Studies
with [1-14C]HBCoA and PhaCCc monitored by sodium
dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE)
and autoradiography reveal that the rate of elongation is much faster
than the rate of initiation. Priming with the artificial primer [3H]sTCoA and monitoring for CoA release reveal a single CoA/PhaC,
suggesting that the protein is uniformly loaded and that the elongation
process could be studied. Reaction of sT-PhaCCc with [1-14C]HBCoA revealed that priming with sTCoA increased the uniformity
of elongation, allowing distinct polymerization species to be observed
by SDS–PAGE and autoradiography. However, in the absence of
HBCoA, [3H]sT-PhaC unexpectedly generates [3H]sDCoA with a rate constant of 0.017 s–1. We propose
that the [3H]sDCoA forms via attack of CoA on the oxoester
of the [3H]sT-PhaC chain, leaving the synthase attached
to a single HB unit. Comparison of the relative rate constants of
thiolysis by CoA and elongation by PhaCCc, and the size
of the PHB polymer generated in vivo, suggests a mechanism for chain
termination and reinitiation.
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Affiliation(s)
- Rachael M Buckley
- †Department of Chemistry and ‡Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - JoAnne Stubbe
- †Department of Chemistry and ‡Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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14
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Numata K, Motoda Y, Watanabe S, Osanai T, Kigawa T. Co-expression of Two Polyhydroxyalkanoate Synthase Subunits from Synechocystis sp. PCC 6803 by Cell-Free Synthesis and Their Specific Activity for Polymerization of 3-Hydroxybutyryl-Coenzyme A. Biochemistry 2015; 54:1401-7. [DOI: 10.1021/bi501560b] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Keiji Numata
- Enzyme
Research Team, RIKEN Center for Sustainable Resource Science, 2-1,
Hirosawa, Wako-shi, Saitama 351-0198, Japan
| | - Yoko Motoda
- Enzyme
Research Team, RIKEN Center for Sustainable Resource Science, 2-1,
Hirosawa, Wako-shi, Saitama 351-0198, Japan
| | - Satoru Watanabe
- Laboratory
for Biomolecular Structure and Dynamics, RIKEN Quantitative Biology Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Takashi Osanai
- Metabolic
Systems Research Team, RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Takanori Kigawa
- Laboratory
for Biomolecular Structure and Dynamics, RIKEN Quantitative Biology Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
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15
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Zhang W, Shrestha R, Buckley RM, Jewell J, Bossmann SH, Stubbe J, Li P. Mechanistic insight with HBCH2CoA as a probe to polyhydroxybutyrate (PHB) synthases. ACS Chem Biol 2014; 9:1773-9. [PMID: 24896226 PMCID: PMC4136709 DOI: 10.1021/cb5002735] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
![]()
Polyhydroxybutyrate (PHB) synthases
catalyze the polymerization
of 3-(R)-hydroxybutyrate coenzyme A (HBCoA) to produce
polyoxoesters of 1–2 MDa. A substrate analogue HBCH2CoA, in which the S in HBCoA is replaced with a
CH2 group, was synthesized in 13 steps using a chemoenzymatic
approach in a 7.5% overall yield. Kinetic studies reveal it is a competitive
inhibitor of a class I and a class III PHB synthases, with Kis of 40 and 14 μM, respectively. To probe
the elongation steps of the polymerization, HBCH2CoA was
incubated with a synthase acylated with a [3H]-saturated
trimer-CoA ([3H]-sTCoA). The products of the reaction were
shown to be the methylene analogue of [3H]-sTCoA ([3H]-sT-CH2-CoA), saturated dimer-([3H]-sD-CO2H), and trimer-acid ([3H]-sT-CO2H),
distinct from the expected methylene analogue of [3H]-saturated
tetramer-CoA ([3H]-sTet-CH2-CoA). Detection
of [3H]-sT-CH2-CoA and its slow rate of formation
suggest that HBCH2CoA may be reporting on the termination
and repriming process of the synthases, rather than elongation.
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Affiliation(s)
- Wei Zhang
- Department
of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
| | - Ruben Shrestha
- Department
of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
| | | | - Jamie Jewell
- Department
of Chemistry, Ohio Dominican University, Columbus, Ohio 43219, United States
| | - Stefan H. Bossmann
- Department
of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
| | | | - Ping Li
- Department
of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
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16
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Numata K, Morisaki K, Tomizawa S, Ohtani M, Demura T, Miyazaki M, Nogi Y, Deguchi S, Doi Y. Synthesis of poly- and oligo(hydroxyalkanoate)s by deep-sea bacteria, Colwellia spp., Moritella spp., and Shewanella spp. Polym J 2013. [DOI: 10.1038/pj.2013.25] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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17
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Numata K, Motoda Y, Watanabe S, Tochio N, Kigawa T, Doi Y. Active Intermediates of Polyhydroxyalkanoate Synthase from Aeromonas caviae in Polymerization Reaction. Biomacromolecules 2012; 13:3450-5. [DOI: 10.1021/bm301276k] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Keiji Numata
- Enzyme Research Team, RIKEN
Biomass Engineering Program, RIKEN, 2-1
Hirosawa, Wako-shi, Saitama 351-0198, Japan
| | - Yoko Motoda
- Enzyme Research Team, RIKEN
Biomass Engineering Program, RIKEN, 2-1
Hirosawa, Wako-shi, Saitama 351-0198, Japan
| | - Satoru Watanabe
- NMR Pipeline Methodology Research
Team, RIKEN Systems and Structural Biology Center, RIKEN, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Naoya Tochio
- NMR Pipeline Methodology Research
Team, RIKEN Systems and Structural Biology Center, RIKEN, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Takanori Kigawa
- NMR Pipeline Methodology Research
Team, RIKEN Systems and Structural Biology Center, RIKEN, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Yoshiharu Doi
- RIKEN Research Cluster for Innovation, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
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18
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Localization of poly(3-hydroxybutyrate) (PHB) granule-associated proteins during PHB granule formation and identification of two new phasins, PhaP6 and PhaP7, in Ralstonia eutropha H16. J Bacteriol 2012; 194:5909-21. [PMID: 22923598 DOI: 10.1128/jb.00779-12] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Poly(3-hydroxybutyrate) (PHB) granules are covered by a surface layer consisting of mainly phasins and other PHB granule-associated proteins (PGAPs). Phasins are small amphiphilic proteins that determine the number and size of accumulated PHB granules. Five phasin proteins (PhaP1 to PhaP5) are known for Ralstonia eutropha. In this study, we identified three additional potential phasin genes (H16_B1988, H16_B2296, and H16_B2326) by inspection of the R. eutropha genome for sequences with "phasin 2 motifs." To determine whether the corresponding proteins represent true PGAPs, fusions with eYFP (enhanced yellow fluorescent protein) were constructed. Similar fusions of eYFP with PhaP1 to PhaP5 as well as fusions with PHB synthase (PhaC1), an inactive PhaC1 variant (PhaC1-C319A), and PhaC2 were also made. All fusions were investigated in wild-type and PHB-negative backgrounds. Colocalization with PHB granules was found for all PhaC variants and for PhaP1 to PhaP5. Additionally, eYFP fusions with H16_B1988 and H16_B2326 colocalized with PHB. Fusions of H16_B2296 with eYFP, however, did not colocalize with PHB granules but did colocalize with the nucleoid region. Notably, all fusions (except H16_B2296) were soluble in a ΔphaC1 strain. These data confirm that H16_B1988 and H16_B2326 but not H16_B2296 encode true PGAPs, for which we propose the designation PhaP6 (H16_B1988) and PhaP7 (H16_B2326). When localization of phasins was investigated at different stages of PHB accumulation, fusions of PhaP6 and PhaP7 were soluble in the first 3 h under PHB-permissive conditions, although PHB granules appeared after 10 min. At later time points, the fusions colocalized with PHB. Remarkably, PHB granules of strains expressing eYFP fusions with PhaP5, PhaP6, or PhaP7 localized predominantly near the cell poles or in the area of future septum formation. This phenomenon was not observed for the other PGAPs (PhaP1 to PhaP4, PhaC1, PhaC1-C319A, and PhaC2) and indicated that some phasins can have additional functions. A chromosomal deletion of phaP6 or phaP7 had no visible effect on formation of PHB granules.
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19
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Tomizawa S, Hyakutake M, Saito Y, Agus J, Mizuno K, Abe H, Tsuge T. Molecular Weight Change of Polyhydroxyalkanoate (PHA) Caused by the PhaC Subunit of PHA Synthase from Bacillus cereus YB-4 in Recombinant Escherichia coli. Biomacromolecules 2011; 12:2660-6. [DOI: 10.1021/bm2004687] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Satoshi Tomizawa
- Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
| | - Manami Hyakutake
- Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
| | - Yuta Saito
- Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
| | - Jumiarti Agus
- Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
| | - Kouhei Mizuno
- Division of Biochemical Engineering, Department of Materials Science and Chemical Engineering, Kitakyushu National College of Technology, 5-20-1 Shii, Kokuraminami-ku, Kitakyushu 802-0985, Japan
| | - Hideki Abe
- Bioplastic Research Team, RIKEN Biomass Engineering Program, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
| | - Takeharu Tsuge
- Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
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20
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21
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Li P, Chakraborty S, Stubbe J. Detection of covalent and noncovalent intermediates in the polymerization reaction catalyzed by a C149S class III polyhydroxybutyrate synthase. Biochemistry 2009; 48:9202-11. [PMID: 19711985 DOI: 10.1021/bi901329b] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Polyhydroxybutyrate (PHB) synthases catalyze the conversion of 3-hydroxybutyryl coenzyme A (HBCoA) to PHB with a molecular mass of 1.5 MDa. The class III synthase from Allochromatium vinosum is a tetramer of PhaEPhaC (each 40 kDa). The polymerization involves covalent catalysis using C149 of PhaC with one PHB chain per PhaEC dimer. Two mechanisms for elongation have been proposed. The first involves an active site composed of two monomers in which the growing hydroxybutyrate (HB) chain alternates between C149 on each monomer. The second involves C149 and covalent and noncovalent (HB)(n)CoA intermediates. Two approaches were investigated to distinguish between these models. The first involved the wild-type (wt) PhaEC primed with sTCoA [a CoA ester of (HB)(3) in which the terminal HO group is replaced with an H] which uniformly loads the enzyme. The primed synthase was reacted with [1-(14)C]HBCoA by a rapid chemical quench method and analyzed for covalent and noncovalent intermediates. Radiolabel was found only with the protein. The second approach used C149S-PhaEC which catalyzes polymer formation at (1)/(2200) of the rate of wt-PhaEC (1.79 min(-1) vs 3900 min(-1)). C149S-PhaEC was incubated with [1-(14)C]HBCoA and chemically quenched on the minute time scale to reveal noncovalently bound [1-(14)C](HB)(2)CoA and (HB)(3)CoA as well as covalently labeled protein. Synthesized (HB)(n)CoA (n = 2 or 3) was shown to acylate PhaEC with rate constants of 1-2 min(-1), and these species were converted into polymer. Thus, the (HB)(n)CoA analogues function as kinetically and chemically competent intermediates. These results support the mechanism involving covalently and noncovalently bound intermediates.
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Affiliation(s)
- Ping Li
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
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22
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Grage K, Jahns AC, Parlane N, Palanisamy R, Rasiah IA, Atwood JA, Rehm BHA. Bacterial Polyhydroxyalkanoate Granules: Biogenesis, Structure, and Potential Use as Nano-/Micro-Beads in Biotechnological and Biomedical Applications. Biomacromolecules 2009; 10:660-9. [DOI: 10.1021/bm801394s] [Citation(s) in RCA: 203] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Katrin Grage
- Institute of Molecular Biosciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand and Hopkirk Research Institute, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - Anika C. Jahns
- Institute of Molecular Biosciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand and Hopkirk Research Institute, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - Natalie Parlane
- Institute of Molecular Biosciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand and Hopkirk Research Institute, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - Rajasekaran Palanisamy
- Institute of Molecular Biosciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand and Hopkirk Research Institute, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - Indira A. Rasiah
- Institute of Molecular Biosciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand and Hopkirk Research Institute, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - Jane A. Atwood
- Institute of Molecular Biosciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand and Hopkirk Research Institute, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
| | - Bernd H. A. Rehm
- Institute of Molecular Biosciences, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand and Hopkirk Research Institute, Massey University, Private Bag 11222, Palmerston North 4442, New Zealand
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23
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Atwood JA, Rehm BHA. Protein engineering towards biotechnological production of bifunctional polyester beads. Biotechnol Lett 2008; 31:131-7. [DOI: 10.1007/s10529-008-9836-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Revised: 08/24/2008] [Accepted: 08/27/2008] [Indexed: 11/28/2022]
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24
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Han J, Lu Q, Zhou L, Zhou J, Xiang H. Molecular characterization of the phaECHm genes, required for biosynthesis of poly(3-hydroxybutyrate) in the extremely halophilic archaeon Haloarcula marismortui. Appl Environ Microbiol 2007; 73:6058-65. [PMID: 17675423 PMCID: PMC2075026 DOI: 10.1128/aem.00953-07] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Although many haloarchaea produce biodegradable polyhydroxyalkanoates (PHAs), the genes involved in PHA synthesis in the domain of Archaea have not yet been experimentally investigated yet. In this study, we revealed that Haloarcula marismortui was able to accumulate poly(3-hydroxybutyrate) (PHB) up to 21% of cellular dry weight when cultured in a minimal medium with excessive glucose and identified the phaE(Hm) and phaC(Hm) genes, probably encoding two subunits of a class III PHA synthase. These two genes were adjacent and directed by a single promoter located 26 bp upstream of the transcriptional start site and were constitutively expressed under both nutrient-rich and -limited conditions. Interestingly, PhaC(Hm) was revealed to be strongly bound with the PHB granules, but PhaE(Hm) seemed not to be. Introduction of either the phaE(Hm) or phaC(Hm) gene into Haloarcula hispanica, which harbors highly homologous phaEC(Hh) genes, could enhance the PHB synthesis in the recombinant strains, while coexpression of the both genes always generated the highest PHB yield. Significantly, knockout of the phaEC(Hh) genes in H. hispanica led to a complete loss of the PHA synthase activity. Complementation with phaEC(Hm) genes, but not a single one, restored the capability of PHB accumulation as well as the PHA synthase activity in this phaEC-deleted haloarchaeon. These results indicated that the phaEC genes are required for biosynthesis of PHB and might encode an active PHA synthase in the Haloarcula species.
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Affiliation(s)
- Jing Han
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing 100101, People's Republic of China
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25
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Tian J, Sinskey AJ, Stubbe J. Kinetic studies of polyhydroxybutyrate granule formation in Wautersia eutropha H16 by transmission electron microscopy. J Bacteriol 2005; 187:3814-24. [PMID: 15901706 PMCID: PMC1112049 DOI: 10.1128/jb.187.11.3814-3824.2005] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Wautersia eutropha, formerly known as Ralstonia eutropha, a gram-negative bacterium, accumulates polyhydroxybutyrate (PHB) as insoluble granules inside the cell when nutrients other than carbon are limited. In this paper, we report findings from kinetic studies of granule formation and degradation in W. eutropha H16 obtained using transmission electron microscopy (TEM). In nitrogen-limited growth medium, the phenotype of the cells at the early stages of granule formation was revealed for the first time. At the center of the cells, dark-stained "mediation elements" with small granules attached were observed. These mediation elements are proposed to serve as nucleation sites for granule initiation. TEM images also revealed that when W. eutropha cells were introduced into nitrogen-limited medium from nutrient-rich medium, the cell size increased two- to threefold, and the cells underwent additional volume changes during growth. Unbiased stereology was used to analyze the two-dimensional TEM images, from which the average volume of a W. eutropha H16 cell and the total surface area of granules per cell in nutrient-rich and PHB production media were obtained. These parameters were essential in the calculation of the concentration of proteins involved in PHB formation and utilization and their changes with time. The extent of protein coverage of the granule surface area is presented in the accompanying paper.
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Affiliation(s)
- Jiamin Tian
- Department of Chemistry, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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26
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Stubbe J, Tian J, He A, Sinskey AJ, Lawrence AG, Liu P. NONTEMPLATE-DEPENDENT POLYMERIZATION PROCESSES: Polyhydroxyalkanoate Synthases as a Paradigm. Annu Rev Biochem 2005; 74:433-80. [PMID: 15952894 DOI: 10.1146/annurev.biochem.74.082803.133013] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This review focuses on nontemplate-dependent polymerases that use water-soluble substrates and convert them into water-insoluble polymers that form granules or inclusions within the cell. The initial part of the review summarizes briefly the current knowledge of polymer formation catalyzed by starch and glycogen synthases, polyphosphate kinase (a polymerase), cyanophycin synthetases, and rubber synthases. Specifically, our current understanding of their mechanisms of initiation, elongation (including granule formation), termination, remodeling, and polymer reutilization will be presented. General underlying principles that govern these types of polymerization reactions will be enumerated as a paradigm for all nontemplate-dependent polymerizations. The bulk of the review then focuses on polyhydroxyalkanoate (PHA) synthases that generate polyoxoesters. These enzymes are of interest as they generate biodegradable polymers. Our current knowledge of PHA production and utilization in vitro and in vivo as well as the contribution of many proteins to these processes will be reviewed.
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Affiliation(s)
- Joanne Stubbe
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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