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Chen T, Hojka M, Davey P, Sun Y, Dykes GF, Zhou F, Lawson T, Nixon PJ, Lin Y, Liu LN. Engineering α-carboxysomes into plant chloroplasts to support autotrophic photosynthesis. Nat Commun 2023; 14:2118. [PMID: 37185249 PMCID: PMC10130085 DOI: 10.1038/s41467-023-37490-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 03/17/2023] [Indexed: 05/17/2023] Open
Abstract
The growth in world population, climate change, and resource scarcity necessitate a sustainable increase in crop productivity. Photosynthesis in major crops is limited by the inefficiency of the key CO2-fixing enzyme Rubisco, owing to its low carboxylation rate and poor ability to discriminate between CO2 and O2. In cyanobacteria and proteobacteria, carboxysomes function as the central CO2-fixing organelles that elevate CO2 levels around encapsulated Rubisco to enhance carboxylation. There is growing interest in engineering carboxysomes into crop chloroplasts as a potential route for improving photosynthesis and crop yields. Here, we generate morphologically correct carboxysomes in tobacco chloroplasts by transforming nine carboxysome genetic components derived from a proteobacterium. The chloroplast-expressed carboxysomes display a structural and functional integrity comparable to native carboxysomes and support autotrophic growth and photosynthesis of the transplastomic plants at elevated CO2. Our study provides proof-of-concept for a route to engineering fully functional CO2-fixing modules and entire CO2-concentrating mechanisms into chloroplasts to improve crop photosynthesis and productivity.
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Affiliation(s)
- Taiyu Chen
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research, Huazhong Agricultural University, 430070, Wuhan, China
| | - Marta Hojka
- Department of Life Sciences, Sir Ernst Chain Building-Wolfson Laboratories, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK
| | - Philip Davey
- School of Life Sciences, University of Essex, Colchester, CO4 4SQ, UK
| | - Yaqi Sun
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK
| | - Gregory F Dykes
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK
| | - Fei Zhou
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research, Huazhong Agricultural University, 430070, Wuhan, China
| | - Tracy Lawson
- School of Life Sciences, University of Essex, Colchester, CO4 4SQ, UK
| | - Peter J Nixon
- Department of Life Sciences, Sir Ernst Chain Building-Wolfson Laboratories, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK
| | - Yongjun Lin
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research, Huazhong Agricultural University, 430070, Wuhan, China.
| | - Lu-Ning Liu
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK.
- College of Marine Life Sciences, and Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ocean University of China, 266003, Qingdao, China.
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2
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Chen T, Riaz S, Davey P, Zhao Z, Sun Y, Dykes GF, Zhou F, Hartwell J, Lawson T, Nixon PJ, Lin Y, Liu LN. Producing fast and active Rubisco in tobacco to enhance photosynthesis. THE PLANT CELL 2023; 35:795-807. [PMID: 36471570 PMCID: PMC9940876 DOI: 10.1093/plcell/koac348] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 10/24/2022] [Accepted: 12/02/2022] [Indexed: 05/28/2023]
Abstract
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) performs most of the carbon fixation on Earth. However, plant Rubisco is an intrinsically inefficient enzyme given its low carboxylation rate, representing a major limitation to photosynthesis. Replacing endogenous plant Rubisco with a faster Rubisco is anticipated to enhance crop photosynthesis and productivity. However, the requirement of chaperones for Rubisco expression and assembly has obstructed the efficient production of functional foreign Rubisco in chloroplasts. Here, we report the engineering of a Form 1A Rubisco from the proteobacterium Halothiobacillus neapolitanus in Escherichia coli and tobacco (Nicotiana tabacum) chloroplasts without any cognate chaperones. The native tobacco gene encoding Rubisco large subunit was genetically replaced with H. neapolitanus Rubisco (HnRubisco) large and small subunit genes. We show that HnRubisco subunits can form functional L8S8 hexadecamers in tobacco chloroplasts at high efficiency, accounting for ∼40% of the wild-type tobacco Rubisco content. The chloroplast-expressed HnRubisco displayed a ∼2-fold greater carboxylation rate and supported a similar autotrophic growth rate of transgenic plants to that of wild-type in air supplemented with 1% CO2. This study represents a step toward the engineering of a fast and highly active Rubisco in chloroplasts to improve crop photosynthesis and growth.
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Affiliation(s)
- Taiyu Chen
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research, Huazhong Agricultural University, Wuhan 430070, China
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
| | - Saba Riaz
- Department of Life Sciences, Sir Ernst Chain Building-Wolfson Laboratories, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Philip Davey
- School of Life Sciences, University of Essex, Colchester CO4 4SQ, UK
| | - Ziyu Zhao
- Department of Life Sciences, Sir Ernst Chain Building-Wolfson Laboratories, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Yaqi Sun
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
| | - Gregory F Dykes
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
| | - Fei Zhou
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research, Huazhong Agricultural University, Wuhan 430070, China
| | - James Hartwell
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
| | - Tracy Lawson
- School of Life Sciences, University of Essex, Colchester CO4 4SQ, UK
| | - Peter J Nixon
- Department of Life Sciences, Sir Ernst Chain Building-Wolfson Laboratories, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Yongjun Lin
- National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research, Huazhong Agricultural University, Wuhan 430070, China
| | - Lu-Ning Liu
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
- College of Marine Life Sciences, and Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ocean University of China, Qingdao 266003, China
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Tan YH, Poong SW, Yang CH, Lim PE, John B, Pai TW, Phang SM. Transcriptomic analysis reveals distinct mechanisms of adaptation of a polar picophytoplankter under ocean acidification conditions. MARINE ENVIRONMENTAL RESEARCH 2022; 182:105782. [PMID: 36308800 DOI: 10.1016/j.marenvres.2022.105782] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Revised: 10/12/2022] [Accepted: 10/14/2022] [Indexed: 06/16/2023]
Abstract
Human emissions of carbon dioxide are causing irreversible changes in our oceans and impacting marine phytoplankton, including a group of small green algae known as picochlorophytes. Picochlorophytes grown in natural phytoplankton communities under future predicted levels of carbon dioxide have been demonstrated to thrive, along with redistribution of the cellular metabolome that enhances growth rate and photosynthesis. Here, using next-generation sequencing technology, we measured levels of transcripts in a picochlorophyte Chlorella, isolated from the sub-Antarctic and acclimated under high and current ambient CO2 levels, to better understand the molecular mechanisms involved with its ability to acclimate to elevated CO2. Compared to other phytoplankton taxa that induce broad transcriptomic responses involving multiple parts of their cellular metabolism, the changes observed in Chlorella focused on activating gene regulation involved in different sets of pathways such as light harvesting complex binding proteins, amino acid synthesis and RNA modification, while carbon metabolism was largely unaffected. Triggering a specific set of genes could be a unique strategy of small green phytoplankton under high CO2 in polar oceans.
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Affiliation(s)
- Yong-Hao Tan
- Institute for Advanced Studies, University of Malaya, Kuala Lumpur, Malaysia; Institute of Ocean & Earth Sciences, University of Malaya, Kuala Lumpur, Malaysia
| | - Sze-Wan Poong
- Institute of Ocean & Earth Sciences, University of Malaya, Kuala Lumpur, Malaysia
| | - Cing-Han Yang
- Department of Computer Science and Engineering, National Taiwan Ocean University, Keelung, Taiwan
| | - Phaik-Eem Lim
- Institute of Ocean & Earth Sciences, University of Malaya, Kuala Lumpur, Malaysia.
| | - Beardall John
- School of Biological Sciences, Monash University, Clayton, Australia
| | - Tun-Wen Pai
- Department of Computer Science and Engineering, National Taiwan Ocean University, Keelung, Taiwan; Department of Computer Science and Information Engineering, National Taipei University of Technology, Taipei, Taiwan
| | - Siew-Moi Phang
- Institute of Ocean & Earth Sciences, University of Malaya, Kuala Lumpur, Malaysia; Department of Biotechnology, Faculty of Applied Science, UCSI University, Kuala Lumpur, Malaysia; The Chancellery, UCSI University, Kuala Lumpur, Malaysia
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4
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Huang J, Jiang Q, Yang M, Dykes GF, Weetman SL, Xin W, He HL, Liu LN. Probing the Internal pH and Permeability of a Carboxysome Shell. Biomacromolecules 2022; 23:4339-4348. [PMID: 36054822 PMCID: PMC9554877 DOI: 10.1021/acs.biomac.2c00781] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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The carboxysome is a protein-based nanoscale organelle
in cyanobacteria
and many proteobacteria, which encapsulates the key CO2-fixing enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)
and carbonic anhydrase (CA) within a polyhedral protein shell. The
intrinsic self-assembly and architectural features of carboxysomes
and the semipermeability of the protein shell provide the foundation
for the accumulation of CO2 within carboxysomes and enhanced
carboxylation. Here, we develop an approach to determine the interior
pH conditions and inorganic carbon accumulation within an α-carboxysome
shell derived from a chemoautotrophic proteobacterium Halothiobacillus neapolitanus and evaluate the shell
permeability. By incorporating a pH reporter, pHluorin2, within empty
α-carboxysome shells produced in Escherichia
coli, we probe the interior pH of the protein shells
with and without CA. Our in vivo and in vitro results demonstrate a lower interior pH of α-carboxysome shells
than the cytoplasmic pH and buffer pH, as well as the modulation of
the interior pH in response to changes in external environments, indicating
the shell permeability to bicarbonate ions and protons. We further
determine the saturated HCO3– concentration
of 15 mM within α-carboxysome shells and show the CA-mediated
increase in the interior CO2 level. Uncovering the interior
physiochemical microenvironment of carboxysomes is crucial for understanding
the mechanisms underlying carboxysomal shell permeability and enhancement
of Rubisco carboxylation within carboxysomes. Such fundamental knowledge
may inform reprogramming carboxysomes to improve metabolism and recruit
foreign enzymes for enhanced catalytical performance.
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Affiliation(s)
- Jiafeng Huang
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom.,School of Life Sciences, Central South University, Changsha 410017, China
| | - Qiuyao Jiang
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom.,Department of Central Laboratory, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, China
| | - Mengru Yang
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom
| | - Gregory F Dykes
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom
| | - Samantha L Weetman
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom
| | - Wei Xin
- Department of Central Laboratory, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, China.,Medical Science and Technology Innovation Center, Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan 271000, China
| | - Hai-Lun He
- School of Life Sciences, Central South University, Changsha 410017, China
| | - Lu-Ning Liu
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom.,College of Marine Life Sciences, and Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ocean University of China, Qingdao 266003, China
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5
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Liu LN. Advances in the bacterial organelles for CO 2 fixation. Trends Microbiol 2021; 30:567-580. [PMID: 34802870 DOI: 10.1016/j.tim.2021.10.004] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 10/19/2021] [Accepted: 10/22/2021] [Indexed: 02/08/2023]
Abstract
Carboxysomes are a family of bacterial microcompartments (BMCs), present in all cyanobacteria and some proteobacteria, which encapsulate the primary CO2-fixing enzyme, Rubisco, within a virus-like polyhedral protein shell. Carboxysomes provide significantly elevated levels of CO2 around Rubisco to maximize carboxylation and reduce wasteful photorespiration, thus functioning as the central CO2-fixation organelles of bacterial CO2-concentration mechanisms. Their intriguing architectural features allow carboxysomes to make a vast contribution to carbon assimilation on a global scale. In this review, we discuss recent research progress that provides new insights into the mechanisms of how carboxysomes are assembled and functionally maintained in bacteria and recent advances in synthetic biology to repurpose the metabolic module in diverse applications.
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Affiliation(s)
- Lu-Ning Liu
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK; College of Marine Life Sciences, and Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ocean University of China, 266003 Qingdao, China.
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6
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Rottet S, Förster B, Hee WY, Rourke LM, Price GD, Long BM. Engineered Accumulation of Bicarbonate in Plant Chloroplasts: Known Knowns and Known Unknowns. FRONTIERS IN PLANT SCIENCE 2021; 12:727118. [PMID: 34531888 PMCID: PMC8438413 DOI: 10.3389/fpls.2021.727118] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Accepted: 08/06/2021] [Indexed: 05/10/2023]
Abstract
Heterologous synthesis of a biophysical CO2-concentrating mechanism (CCM) in plant chloroplasts offers significant potential to improve the photosynthetic efficiency of C3 plants and could translate into substantial increases in crop yield. In organisms utilizing a biophysical CCM, this mechanism efficiently surrounds a high turnover rate Rubisco with elevated CO2 concentrations to maximize carboxylation rates. A critical feature of both native biophysical CCMs and one engineered into a C3 plant chloroplast is functional bicarbonate (HCO3 -) transporters and vectorial CO2-to-HCO3 - converters. Engineering strategies aim to locate these transporters and conversion systems to the C3 chloroplast, enabling elevation of HCO3 - concentrations within the chloroplast stroma. Several CCM components have been identified in proteobacteria, cyanobacteria, and microalgae as likely candidates for this approach, yet their successful functional expression in C3 plant chloroplasts remains elusive. Here, we discuss the challenges in expressing and regulating functional HCO3 - transporter, and CO2-to-HCO3 - converter candidates in chloroplast membranes as an essential step in engineering a biophysical CCM within plant chloroplasts. We highlight the broad technical and physiological concerns which must be considered in proposed engineering strategies, and present our current status of both knowledge and knowledge-gaps which will affect successful engineering outcomes.
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Affiliation(s)
- Sarah Rottet
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
| | - Britta Förster
- Australian Research Council Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra, ACT, Australia
| | - Wei Yih Hee
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
| | - Loraine M. Rourke
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
| | - G. Dean Price
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
- Australian Research Council Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra, ACT, Australia
| | - Benedict M. Long
- Realizing Increased Photosynthetic Efficiency (RIPE), The Australian National University, Canberra, ACT, Australia
- Australian Research Council Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Canberra, ACT, Australia
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7
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Huokko T, Ni T, Dykes GF, Simpson DM, Brownridge P, Conradi FD, Beynon RJ, Nixon PJ, Mullineaux CW, Zhang P, Liu LN. Probing the biogenesis pathway and dynamics of thylakoid membranes. Nat Commun 2021; 12:3475. [PMID: 34108457 PMCID: PMC8190092 DOI: 10.1038/s41467-021-23680-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 05/11/2021] [Indexed: 01/30/2023] Open
Abstract
How thylakoid membranes are generated to form a metabolically active membrane network and how thylakoid membranes orchestrate the insertion and localization of protein complexes for efficient electron flux remain elusive. Here, we develop a method to modulate thylakoid biogenesis in the rod-shaped cyanobacterium Synechococcus elongatus PCC 7942 by modulating light intensity during cell growth, and probe the spatial-temporal stepwise biogenesis process of thylakoid membranes in cells. Our results reveal that the plasma membrane and regularly arranged concentric thylakoid layers have no physical connections. The newly synthesized thylakoid membrane fragments emerge between the plasma membrane and pre-existing thylakoids. Photosystem I monomers appear in the thylakoid membranes earlier than other mature photosystem assemblies, followed by generation of Photosystem I trimers and Photosystem II complexes. Redistribution of photosynthetic complexes during thylakoid biogenesis ensures establishment of the spatial organization of the functional thylakoid network. This study provides insights into the dynamic biogenesis process and maturation of the functional photosynthetic machinery.
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Affiliation(s)
- Tuomas Huokko
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - Tao Ni
- Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK
| | - Gregory F Dykes
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - Deborah M Simpson
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - Philip Brownridge
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - Fabian D Conradi
- School of Biological and Chemical Sciences, Queen Mary University of London, London, UK
| | - Robert J Beynon
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - Peter J Nixon
- Department of Life Sciences, Imperial College London, London, UK
| | - Conrad W Mullineaux
- School of Biological and Chemical Sciences, Queen Mary University of London, London, UK
| | - Peijun Zhang
- Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, UK
- Electron Bio-Imaging Centre, Diamond Light Source, Harwell Science and Innovation Campus, Didcot, UK
| | - Lu-Ning Liu
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK.
- College of Marine Life Sciences, and Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ocean University of China, Qingdao, China.
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8
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Molecular mechanism underlying transport and allosteric inhibition of bicarbonate transporter SbtA. Proc Natl Acad Sci U S A 2021; 118:2101632118. [PMID: 34031249 DOI: 10.1073/pnas.2101632118] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
SbtA is a high-affinity, sodium-dependent bicarbonate transporter found in the cyanobacterial CO2-concentrating mechanism (CCM). SbtA forms a complex with SbtB, while SbtB allosterically regulates the transport activity of SbtA by binding with adenyl nucleotides. The underlying mechanism of transport and regulation of SbtA is largely unknown. In this study, we report the three-dimensional structures of the cyanobacterial Synechocystis sp. PCC 6803 SbtA-SbtB complex in both the presence and absence of HCO3 - and/or AMP at 2.7 Å and 3.2 Å resolution. An analysis of the inward-facing state of the SbtA structure reveals the HCO3 -/Na+ binding site, providing evidence for the functional unit as a trimer. A structural comparison found that SbtA adopts an elevator mechanism for bicarbonate transport. A structure-based analysis revealed that the allosteric inhibition of SbtA by SbtB occurs mainly through the T-loop of SbtB, which binds to both the core domain and the scaffold domain of SbtA and locks it in an inward-facing state. T-loop conformation is stabilized by the AMP molecules binding at the SbtB trimer interfaces and may be adjusted by other adenyl nucleotides. The unique regulatory mechanism of SbtA by SbtB makes it important to study inorganic carbon uptake systems in CCM, which can be used to modify photosynthesis in crops.
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Sun Y, Huang F, Dykes GF, Liu LN. Diurnal Regulation of In Vivo Localization and CO 2-Fixing Activity of Carboxysomes in Synechococcus elongatus PCC 7942. Life (Basel) 2020; 10:E169. [PMID: 32872408 PMCID: PMC7555275 DOI: 10.3390/life10090169] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 08/23/2020] [Accepted: 08/27/2020] [Indexed: 12/13/2022] Open
Abstract
Carboxysomes are the specific CO2-fixing microcompartments in all cyanobacteria. Although it is known that the organization and subcellular localization of carboxysomes are dependent on external light conditions and are highly relevant to their functions, how carboxysome organization and function are actively orchestrated in natural diurnal cycles has remained elusive. Here, we explore the dynamic regulation of carboxysome positioning and carbon fixation in the model cyanobacterium Synechococcus elongatus PCC 7942 in response to diurnal light-dark cycles, using live-cell confocal imaging and Rubisco assays. We found that carboxysomes are prone to locate close to the central line along the short axis of the cell and exhibit a greater preference of polar distribution in the dark phase, coupled with a reduction in carbon fixation. Moreover, we show that deleting the gene encoding the circadian clock protein KaiA could lead to an increase in carboxysome numbers per cell and reduced portions of pole-located carboxysomes. Our study provides insight into the diurnal regulation of carbon fixation in cyanobacteria and the general cellular strategies of cyanobacteria living in natural habitat for environmental acclimation.
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Affiliation(s)
| | | | | | - Lu-Ning Liu
- Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK; (Y.S.); (F.H.); (G.F.D.)
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10
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Rubisco accumulation factor 1 (Raf1) plays essential roles in mediating Rubisco assembly and carboxysome biogenesis. Proc Natl Acad Sci U S A 2020; 117:17418-17428. [PMID: 32636267 PMCID: PMC7382273 DOI: 10.1073/pnas.2007990117] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Carboxysomes are membrane-free organelles for carbon assimilation in cyanobacteria. The carboxysome consists of a proteinaceous shell that structurally resembles virus capsids and internal enzymes including ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), the primary carbon-fixing enzyme in photosynthesis. The formation of carboxysomes requires hierarchical self-assembly of thousands of protein subunits, initiated from Rubisco assembly and packaging to shell encapsulation. Here we study the role of Rubisco assembly factor 1 (Raf1) in Rubisco assembly and carboxysome formation in a model cyanobacterium, Synechococcus elongatus PCC7942 (Syn7942). Cryo-electron microscopy reveals that Raf1 facilitates Rubisco assembly by mediating RbcL dimer formation and dimer-dimer interactions. Syn7942 cells lacking Raf1 are unable to form canonical intact carboxysomes but generate a large number of intermediate assemblies comprising Rubisco, CcaA, CcmM, and CcmN without shell encapsulation and a low abundance of carboxysome-like structures with reduced dimensions and irregular shell shapes and internal organization. As a consequence, the Raf1-depleted cells exhibit reduced Rubisco content, CO2-fixing activity, and cell growth. Our results provide mechanistic insight into the chaperone-assisted Rubisco assembly and biogenesis of carboxysomes. Advanced understanding of the biogenesis and stepwise formation process of the biogeochemically important organelle may inform strategies for heterologous engineering of functional CO2-fixing modules to improve photosynthesis.
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