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Choi SH, Lee SS, Lee HY, Kim S, Kim JW, Jin MS. Cryo-EM structure of cadmium-bound human ABCB6. Commun Biol 2024; 7:672. [PMID: 38822018 PMCID: PMC11143254 DOI: 10.1038/s42003-024-06377-1] [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: 09/22/2023] [Accepted: 05/23/2024] [Indexed: 06/02/2024] Open
Abstract
ATP-binding cassette transporter B6 (ABCB6), a protein essential for heme biosynthesis in mitochondria, also functions as a heavy metal efflux pump. Here, we present cryo-electron microscopy structures of human ABCB6 bound to a cadmium Cd(II) ion in the presence of antioxidant thiol peptides glutathione (GSH) and phytochelatin 2 (PC2) at resolutions of 3.2 and 3.1 Å, respectively. The overall folding of the two structures resembles the inward-facing apo state but with less separation between the two halves of the transporter. Two GSH molecules are symmetrically bound to the Cd(II) ion in a bent conformation, with the central cysteine protruding towards the metal. The N-terminal glutamate and C-terminal glycine of GSH do not directly interact with Cd(II) but contribute to neutralizing positive charges of the binding cavity by forming hydrogen bonds and van der Waals interactions with nearby residues. In the presence of PC2, Cd(II) binding to ABCB6 is similar to that observed with GSH, except that two cysteine residues of each PC2 molecule participate in Cd(II) coordination to form a tetrathiolate. Structural comparison of human ABCB6 and its homologous Atm-type transporters indicate that their distinct substrate specificity might be attributed to variations in the capping residues situated at the top of the substrate-binding cavity.
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Affiliation(s)
- Seung Hun Choi
- School of Life Sciences, GIST, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, Republic of Korea
| | - Sang Soo Lee
- School of Life Sciences, GIST, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, Republic of Korea
| | - Hyeon You Lee
- School of Life Sciences, GIST, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, Republic of Korea
| | - Subin Kim
- School of Life Sciences, GIST, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, Republic of Korea
| | - Ji Won Kim
- Department of Life Sciences, POSTECH, 77 Cheongam-Ro, Nam-gu, Pohang, Republic of Korea
| | - Mi Sun Jin
- School of Life Sciences, GIST, 123 Cheomdangwagi-ro, Buk-gu, Gwangju, Republic of Korea.
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Thiriet-Rupert S, Gain G, Jadoul A, Vigneron A, Bosman B, Carnol M, Motte P, Cardol P, Nouet C, Hanikenne M. Long-term acclimation to cadmium exposure reveals extensive phenotypic plasticity in Chlamydomonas. PLANT PHYSIOLOGY 2021; 187:1653-1678. [PMID: 34618070 PMCID: PMC8566208 DOI: 10.1093/plphys/kiab375] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Accepted: 07/17/2021] [Indexed: 05/06/2023]
Abstract
Increasing industrial and anthropogenic activities are producing and releasing more and more pollutants in the environment. Among them, toxic metals are one of the major threats for human health and natural ecosystems. Because photosynthetic organisms play a critical role in primary productivity and pollution management, investigating their response to metal toxicity is of major interest. Here, the green microalga Chlamydomonas (Chlamydomonas reinhardtii) was subjected to short (3 d) or chronic (6 months) exposure to 50 µM cadmium (Cd), and the recovery from chronic exposure was also examined. An extensive phenotypic characterization and transcriptomic analysis showed that the impact of Cd on biomass production of short-term (ST) exposed cells was almost entirely abolished by long-term (LT) acclimation. The underlying mechanisms were initiated at ST and further amplified after LT exposure resulting in a reversible equilibrium allowing biomass production similar to control condition. This included modification of cell wall-related gene expression and biofilm-like structure formation, dynamics of metal ion uptake and homeostasis, photosynthesis efficiency recovery and Cd acclimation through metal homeostasis adjustment. The contribution of the identified coordination of phosphorus and iron homeostasis (partly) mediated by the main phosphorus homeostasis regulator, Phosphate Starvation Response 1, and a basic Helix-Loop-Helix transcription factor (Cre05.g241636) was further investigated. The study reveals the highly dynamic physiological plasticity enabling algal cell growth in an extreme environment.
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Affiliation(s)
- Stanislas Thiriet-Rupert
- InBioS-PhytoSystems, Functional Genomics and Plant Molecular Imaging, University of Liège, 4000 Liège, Belgium
- Present address: Unité de Génétique des Biofilms, Département Microbiologie, Institut Pasteur, Paris, France
| | - Gwenaëlle Gain
- InBioS-PhytoSystems, Functional Genomics and Plant Molecular Imaging, University of Liège, 4000 Liège, Belgium
- InBioS-PhytoSystems, Genetics and Physiology of Microalgae, University of Liège, 4000 Liège, Belgium
| | - Alice Jadoul
- InBioS-PhytoSystems, Functional Genomics and Plant Molecular Imaging, University of Liège, 4000 Liège, Belgium
| | - Amandine Vigneron
- InBioS-PhytoSystems, Functional Genomics and Plant Molecular Imaging, University of Liège, 4000 Liège, Belgium
| | - Bernard Bosman
- InBioS-PhytoSystems, Laboratory of Plant and Microbial Ecology, University of Liège, 4000 Liège, Belgium
| | - Monique Carnol
- InBioS-PhytoSystems, Laboratory of Plant and Microbial Ecology, University of Liège, 4000 Liège, Belgium
| | - Patrick Motte
- InBioS-PhytoSystems, Functional Genomics and Plant Molecular Imaging, University of Liège, 4000 Liège, Belgium
| | - Pierre Cardol
- InBioS-PhytoSystems, Genetics and Physiology of Microalgae, University of Liège, 4000 Liège, Belgium
| | - Cécile Nouet
- InBioS-PhytoSystems, Functional Genomics and Plant Molecular Imaging, University of Liège, 4000 Liège, Belgium
| | - Marc Hanikenne
- InBioS-PhytoSystems, Functional Genomics and Plant Molecular Imaging, University of Liège, 4000 Liège, Belgium
- Author for communication:
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Kim S, Sharma AK, Vatamaniuk OK. N-Terminal Extension and C-Terminal Domains Are Required for ABCB6/HMT-1 Protein Interactions, Function in Cadmium Detoxification, and Localization to the Endosomal-Recycling System in Caenorhabditis elegans. Front Physiol 2018; 9:885. [PMID: 30104978 PMCID: PMC6077975 DOI: 10.3389/fphys.2018.00885] [Citation(s) in RCA: 6] [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: 05/09/2018] [Accepted: 06/19/2018] [Indexed: 01/30/2023] Open
Abstract
The chronic exposure of humans to toxic metals such as cadmium from food and air causes dysfunction of vital organs, neurodegenerative conditions, and cancer. In this regard, members of the ABCB sub-family of the ATP-binding cassette (ABC) transporter superfamily, ABCB6/HMT-1, are acutely required for the detoxification of heavy metals and are present in genomes of many organisms including the nematode worm, Caenorhabditis elegans and humans. We showed previously that C. elegans ABCB6/HMT-1 detoxifies cadmium, copper, and arsenic, and is expressed in liver-like cells, the coelomocytes, head neurons and intestinal cells, which are the cell types that are affected by heavy metal poisoning in humans. The subcellular localization of ABCB6/HMT-1 proteins is unclear. ABCB6/HMT-1 proteins have a distinguishing topology: in addition to one transmembrane domain and one nucleotide-binding domain, they possess a hydrophobic N-terminal extension (NTE) domain encompassing five to six transmembrane spans. The role of the NTE domain in the function of ABCB6/HMT-1 in the native organism remains to be investigated. We used a versatile, multicellular model system, C. elegans, to establish the subcellular localization of ABCB6/HMT-1 and refine its structure-function studies in the native organism. We show that ABCB6/HMT-1 localizes mainly to the apical recycling endosomes and, in part, to early and late endosomes of intestinal cells. We also show that ABCB6/HMT-1 lacking the NTE domain is mistargeted to the plasma membrane and is unable to confer cadmium resistance. Although the NTE domain is essential for ABCB6/HMT-1 interaction with itself, the absence of NTE does not fully prevent this interaction. As a result, ABCB6/HMT-1 lacking the NTE domain, and expressed in wild-type worms or co-expressed with the full-length polypeptide, inactivates and mistargets the full-length ABCB6/HMT-1. We also show that the 43 amino acid residue stretch at the COOH-terminus is required for the ABCB6/HMT-1 interaction with itself and cadmium detoxification function. These results suggest that both NTE and COOH-terminus must be present to allow the protein to interact with itself and confer cadmium resistance. Considering that ABCB6/HMT-1 proteins are highly conserved, this study advances our understanding of how these proteins function in cadmium resistance in different species. Furthermore, these studies uncover the role of the endosomal-recycling system in cadmium detoxification.
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Affiliation(s)
- Sungjin Kim
- Section of Soil and Crop Sciences, School of Integrative Plant Science, Cornell University, Ithaca, NY, United States
| | - Anuj K. Sharma
- Section of Soil and Crop Sciences, School of Integrative Plant Science, Cornell University, Ithaca, NY, United States
| | - Olena K. Vatamaniuk
- Section of Soil and Crop Sciences, School of Integrative Plant Science, Cornell University, Ithaca, NY, United States
- Section of Plant Biology, School of Integrative Plant Science, Cornell University, Ithaca, NY, United States
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Penen F, Isaure MP, Dobritzsch D, Bertalan I, Castillo-Michel H, Proux O, Gontier E, Le Coustumer P, Schaumlöffel D. Pools of cadmium in Chlamydomonas reinhardtii revealed by chemical imaging and XAS spectroscopy. Metallomics 2018; 9:910-923. [PMID: 28598481 DOI: 10.1039/c7mt00029d] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The green micro-alga Chlamydomonas reinhardtii is commonly used as a model to investigate metallic stress in photosynthetic organisms. The aim of this study was to explore processes implemented by three C. reinhardtii strains to cope with cadmium (Cd), and particularly to evidence Cd sequestration in the cell. For that, we used a combination of subcellular fractionation and chemical imaging (micro X-ray fluorescence (μXRF) and transmission electron microscopy (TEM/X-EDS)) to identify subcellular compartments of Cd accumulation, and X-ray absorption spectroscopy (XAS) to determine chemical Cd speciation. C. reinhardtii wild type strain 11/32b (wt), a newly design strain (pcs1) expressing a modified phytochelatin synthase in the chloroplast and a cell wall less strain CC400 (cw15) were exposed to 70 μM Cd. At this Cd concentration, cell vitality was not affected, however, the strains showed various strategies to cope with Cd stress. In wt, most of Cd was diffused in the whole cell, and complexed by thiol ligands, while the other part was associated with phosphate in vacuolar Ca polyphosphate granules. Thiol ligands increased with exposure time, confirming their important role in Cd stress. In pcs1, Cd was also present as vacuolar Ca polyphosphate granules, and diffused in the cell as Cd-thiol complexes. In addition, while it should be regarded with caution, a minor proportion of Cd complexed by carboxyl groups, was potentially provided by starch produced around the pyrenoid and in the chloroplast. Results suggested that pcs1 uses thiol compounds such as PC to a lesser extent for Cd sequestration than wt. In cw15, an excretion of Cd, Ca polyphosphate granules has to be considered. Finally, Cd was detected in the pyrenoid of all strains.
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Affiliation(s)
- F Penen
- Université de Pau et des Pays de l'Adour, CNRS, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux (IPREM), UMR 5254, Hélioparc, 2 avenue Pierre Angot, 64053 Pau, France.
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Kim S, Selote DS, Vatamaniuk OK. The N-terminal extension domain of the C. elegans half-molecule ABC transporter, HMT-1, is required for protein-protein interactions and function. PLoS One 2010; 5:e12938. [PMID: 20886084 PMCID: PMC2944878 DOI: 10.1371/journal.pone.0012938] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2010] [Accepted: 08/31/2010] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Members of the HMT-1 (heavy metal tolerance factor 1) subfamily of the ATP-binding cassette (ABC) transporter superfamily detoxify heavy metals and have unique topology: they are half-molecule ABC transporters that, in addition to a single transmembrane domain (TMD1) and a single nucleotide-binding domain (NBD1), possess a hydrophobic NH2-terminal extension (NTE). These structural features distinguish HMTs from other ABC transporters in different species including Drosophila and humans. Functional ABC transporters, however, are comprised of at least four-domains (two TMDs and two NDBs) formed from either a single polypeptide or by the association of two or four separate subunits. Whether HMTs act as oligomers and what role the NTE domain plays in their function have not been determined. METHODOLOGY/PRINCIPAL FINDINGS In this study, we examined the oligomeric status of Caenorhabditis elegans HMT-1 and the functional significance of its NTE using gel-filtration chromatography in combination with the mating-based split-ubiquitin yeast two-hybrid system (mbSUS) and functional in vivo assays. We found that HMT-1 exists in a protein complex in C. elegans. Studies in S. cerevisiae showed that HMT-1 at a minimum homodimerizes and that oligomerization is essential for HMT-1 to confer cadmium tolerance. We also established that the NTE domain plays an important structural and functional role: it is essential for HMT-1 oligomerization and Cd-detoxification function. However, the NTE itself was not sufficient for oligomerization suggesting that multiple structural features of HMT-1 must associate to form a functional transporter. CONCLUSIONS The prominence of heavy metals as environmental toxins and the remarkable conservation of HMT-1 structural architecture and function in different species reinforce the value of continued studies of HMT-1 in model systems for identifying functional domains in HMT1 of humans.
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Affiliation(s)
- Sungjin Kim
- Department of Crop and Soil Sciences, Cornell University, Ithaca, New York, United States of America
| | - Devarshi S. Selote
- Department of Crop and Soil Sciences, Cornell University, Ithaca, New York, United States of America
| | - Olena K. Vatamaniuk
- Department of Crop and Soil Sciences, Cornell University, Ithaca, New York, United States of America
- * E-mail:
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Kovalchuk A, Driessen AJM. Phylogenetic analysis of fungal ABC transporters. BMC Genomics 2010; 11:177. [PMID: 20233411 PMCID: PMC2848647 DOI: 10.1186/1471-2164-11-177] [Citation(s) in RCA: 160] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2009] [Accepted: 03/16/2010] [Indexed: 12/22/2022] Open
Abstract
Background The superfamily of ABC proteins is among the largest known in nature. Its members are mainly, but not exclusively, involved in the transport of a broad range of substrates across biological membranes. Many contribute to multidrug resistance in microbial pathogens and cancer cells. The diversity of ABC proteins in fungi is comparable with those in multicellular animals, but so far fungal ABC proteins have barely been studied. Results We performed a phylogenetic analysis of the ABC proteins extracted from the genomes of 27 fungal species from 18 orders representing 5 fungal phyla thereby covering the most important groups. Our analysis demonstrated that some of the subfamilies of ABC proteins remained highly conserved in fungi, while others have undergone a remarkable group-specific diversification. Members of the various fungal phyla also differed significantly in the number of ABC proteins found in their genomes, which is especially reduced in the yeast S. cerevisiae and S. pombe. Conclusions Data obtained during our analysis should contribute to a better understanding of the diversity of the fungal ABC proteins and provide important clues about their possible biological functions.
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Affiliation(s)
- Andriy Kovalchuk
- Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.
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Schwartz MS, Benci JL, Selote DS, Sharma AK, Chen AGY, Dang H, Fares H, Vatamaniuk OK. Detoxification of multiple heavy metals by a half-molecule ABC transporter, HMT-1, and coelomocytes of Caenorhabditis elegans. PLoS One 2010; 5:e9564. [PMID: 20221439 PMCID: PMC2832763 DOI: 10.1371/journal.pone.0009564] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2009] [Accepted: 02/11/2010] [Indexed: 11/22/2022] Open
Abstract
Background Developing methods for protecting organisms in metal-polluted environments is contingent upon our understanding of cellular detoxification mechanisms. In this regard, half-molecule ATP-binding cassette (ABC) transporters of the HMT-1 subfamily are required for cadmium (Cd) detoxification. HMTs have conserved structural architecture that distinguishes them from other ABC transporters and allows the identification of homologs in genomes of different species including humans. We recently discovered that HMT-1 from the simple, unicellular organism, Schizosaccharomyces pombe, SpHMT1, acts independently of phytochelatin synthase (PCS) and detoxifies Cd, but not other heavy metals. Whether HMTs from multicellular organisms confer tolerance only to Cd or also to other heavy metals is not known. Methodology/Principal Findings Using molecular genetics approaches and functional in vivo assays we showed that HMT-1 from a multicellular organism, Caenorhabditis elegans, functions distinctly from its S. pombe counterpart in that in addition to Cd it confers tolerance to arsenic (As) and copper (Cu) while acting independently of pcs-1. Further investigation of hmt-1 and pcs-1 revealed that these genes are expressed in different cell types, supporting the notion that hmt-1 and pcs-1 operate in distinct detoxification pathways. Interestingly, pcs-1 and hmt-1 are co-expressed in highly endocytic C. elegans cells with unknown function, the coelomocytes. By analyzing heavy metal and oxidative stress sensitivities of the coelomocyte-deficient C. elegans strain we discovered that coelomocytes are essential mainly for detoxification of heavy metals, but not of oxidative stress, a by-product of heavy metal toxicity. Conclusions/Significance We established that HMT-1 from the multicellular organism confers tolerance to multiple heavy metals and is expressed in liver-like cells, the coelomocytes, as well as head neurons and intestinal cells, which are cell types that are affected by heavy metal poisoning in humans. We also showed that coelomocytes are involved in detoxification of heavy metals. Therefore, the HMT-1-dependent detoxification pathway and coelomocytes of C. elegans emerge as novel models for studies of heavy metal-promoted diseases.
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Affiliation(s)
- Marc S. Schwartz
- Department of Crop and Soil Sciences, Cornell University, Ithaca, New York, United States of America
| | - Joseph L. Benci
- Department of Crop and Soil Sciences, Cornell University, Ithaca, New York, United States of America
| | - Devarshi S. Selote
- Department of Crop and Soil Sciences, Cornell University, Ithaca, New York, United States of America
| | - Anuj K. Sharma
- Department of Crop and Soil Sciences, Cornell University, Ithaca, New York, United States of America
| | - Andy G. Y. Chen
- Department of Crop and Soil Sciences, Cornell University, Ithaca, New York, United States of America
| | - Hope Dang
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, United States of America
| | - Hanna Fares
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, United States of America
| | - Olena K. Vatamaniuk
- Department of Crop and Soil Sciences, Cornell University, Ithaca, New York, United States of America
- * E-mail:
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Sooksa-nguan T, Yakubov B, Kozlovskyy VI, Barkume CM, Howe KJ, Thannhauser TW, Rutzke MA, Hart JJ, Kochian LV, Rea PA, Vatamaniuk OK. Drosophila ABC Transporter, DmHMT-1, Confers Tolerance to Cadmium. J Biol Chem 2009; 284:354-362. [DOI: 10.1074/jbc.m806501200] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Wang T, Wu M. An ATP-binding cassette transporter related to yeast vacuolar ScYCF1 is important for Cd sequestration in Chlamydomonas reinhardtii. PLANT, CELL & ENVIRONMENT 2006; 29:1901-12. [PMID: 16930316 DOI: 10.1111/j.1365-3040.2006.01566.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
We generated a Cd-sensitive insertional mutant, Cds18, in Chlamydomonas reinhardtii and elucidated the deletion of a 10 kb fragment containing the promoter and a portion of the coding region for CrMRP2 gene that silenced the transcription of CrMRP2 in mutant Cds18. The association between CrMRP2 and Cd sensitivity was confirmed by complementing mutant Cds18 with a cloned genomic DNA fragment containing the promoter and complete coding sequence for CrMRP2. The genomic region and the full-length cDNA for CrMRP2 were cloned and sequenced. Computer searches detected the significant resemblance of CrMRP2 with HsMRP1, AtMRP3 and ScYCF1, in Homo sapiens, Arabidopsis thaliana and Saccharomyces cerevisiae, respectively. All are members of the multidrug resistance-associated protein (MRP)/cystic fibrosis transmembrane conductance regulator (CFTR) subfamily of ATP-binding cassette (ABC) transporters. When the cDNA of CrMRP2 was cloned into the yeast expression vector pEGKT and transformed into the yeast mutant strain DTY168 lacking ScYCF1, it restored the function of ScYCF1, a yeast vacuolar glutathione (GSH)-conjugate ABC transporter. A putative vacuolar-targeting motif (T/I/K)LP(L/K/I) was detected in the N-terminal part of CrMRP2. In wild-type C. reinhardtii, CrMRP2 transcription was significantly up-regulated upon Cd treatment. Comparing with mutant Cds18, the wild-type algal cells accumulated and sequestered more Cd in the stable high molecular weight (HMW) phytochelatin (PC)-Cd complex; the labile low molecular weight (LMW) PC-Cd complex was detected in mutant Cds18 at an earlier stage of Cd treatment. This study demonstrated the expression of CrMRP2 in C. reinhardtii and implicated its function in the formation/accumulation of stable HMW PC-Cd complex.
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Affiliation(s)
- Tingliang Wang
- Department of Biology, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong Special Administrative Region, China
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Merchant SS, Allen MD, Kropat J, Moseley JL, Long JC, Tottey S, Terauchi AM. Between a rock and a hard place: trace element nutrition in Chlamydomonas. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1763:578-94. [PMID: 16766055 DOI: 10.1016/j.bbamcr.2006.04.007] [Citation(s) in RCA: 187] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2006] [Revised: 04/06/2006] [Accepted: 04/06/2006] [Indexed: 11/23/2022]
Abstract
Photosynthetic organisms are among the earliest life forms on earth and their biochemistry is strictly dependent on a wide range of inorganic nutrients owing to the use of metal cofactor-dependent enzymes in photosynthesis, respiration, inorganic nitrogen and sulfur assimilation. Chlamydomonas reinhardtii is a photosynthetic eukaryotic model organism for the study of trace metal homeostasis. Chlamydomonas spp. are widely distributed and can be found in soil, glaciers, acid mines and sewage ponds, suggesting that the genus has significant capacity for acclimation to micronutrient availability. Analysis of the draft genome indicates that metal homeostasis mechanisms in Chlamydomonas represent a blend of mechanisms operating in animals, plants and microbes. A combination of classical genetics, differential expression and genomic analysis has led to the identification of homologues of components known to operate in fungi and animals (e.g., Fox1, Ftr1, Fre1, Fer1, Ctr1/2) as well as novel molecules involved in copper and iron nutrition (Crr1, Fea1/2). Besides activating iron assimilation pathways, iron-deficient Chlamydomonas cells re-adjust metabolism by reducing light delivery to photosystem I (to avoid photo-oxidative damage resulting from compromised FeS clusters) and by modifying the ferredoxin profile (perhaps to accommodate preferential allocation of reducing equivalents). Up-regulation of a MnSOD isoform may compensate for loss of FeSOD. Ferritin could function to buffer the iron released from programmed degradation of iron-containing enzymes in the chloroplast. Some metabolic adjustments are made in anticipation of deficiency while others occur only with sustained or severe deficiency. Copper-deficient Chlamydomonas cells induce a copper assimilation pathway consisting of a cell surface reductase and a Cu(+) transporter (presumed CTR homologue). There are metabolic adaptations in addition: the synthesis of "back-up" enzymes for plastocyanin in photosynthesis and the ferroxidase in iron assimilation plus activation of alternative oxidase to handle the electron "overflow" resulting from reduced cytochrome oxidase function. Oxygen-dependent enzymes in the tetrapyrrole pathway (coproporphyrinogen oxidase and aerobic oxidative cyclase) are also increased in expression and activity by as much as 10-fold but the connection between copper nutrition and tetrapyrroles is not understood. The copper-deficiency responses are mediated by copper response elements that are defined by a GTAC core sequence and a novel metalloregulator, Crr1, which uses a zinc-dependent SBP domain to bind to the CuRE. The Chlamydomonas model is ideal for future investigation of nutritional manganese deficiency and selenoenzyme function. It is also suited for studies of trace nutrient interactions, nutrition-dependent metabolic changes, the relationship between photo-oxidative stress and metal homeostasis, and the important questions of differential allocation of limiting metal nutrients (e.g., to respiration vs. photosynthesis).
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Affiliation(s)
- Sabeeha S Merchant
- Department of Chemistry and Biochemistry, Box 951569, University of California-Los Angeles, Los Angeles, CA 90095-1569, USA.
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Hanikenne M, Krämer U, Demoulin V, Baurain D. A comparative inventory of metal transporters in the green alga Chlamydomonas reinhardtii and the red alga Cyanidioschizon merolae. PLANT PHYSIOLOGY 2005; 137:428-46. [PMID: 15710683 PMCID: PMC1065346 DOI: 10.1104/pp.104.054189] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2004] [Revised: 11/16/2004] [Accepted: 11/18/2004] [Indexed: 05/20/2023]
Affiliation(s)
- Marc Hanikenne
- Metal Homeostasis Group, Max Planck Institute for Plant Molecular Physiology, 14476 Golm, Germany.
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Abstract
In this study, the effects of 1 mM sodium nitrite, a reactive nitrogen species (RNS) generator, and 0.5 mM paraquat, which produces reactive oxygen species (ROS), on gene expression in the marine dinoflagellate species Pyrocystis lunula were investigated using microarrays containing 3500 complementary DNAs (cDNAs). A total of 246 differentially expressed genes were identified under these treatments: 204 genes were specifically regulated in response to nitrite and 37 genes specifically to paraquat. Only six genes showed a dependence on both nitrite and paraquat, indicating that the two agents act predominantly via distinct pathways. Although many of these redox-regulated genes encode proteins from a diverse range of functional categories, the majority of them (68%) represent novel sequences. Temporary abnormal spherical cells occurred in nitrite-treated cultures, but not in those exposed to paraquat, suggesting that this response involves a specific pathway triggered by RNS. The genes involved include one that encodes a transcription factor unique to dinoflagellates (HPl), and genes encoding proteins similar to those regulating developmental processes in plants and animals such as NYD-SP5, shaggy and calcium-dependent kinases, the COP9 signalosome complex, ubiquitin-related proteases and a metacaspase.
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Affiliation(s)
- O Keith Okamoto
- Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138-2020, USA
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Hanikenne M. Chlamydomonas reinhardtii as a eukaryotic photosynthetic model for studies of heavy metal homeostasis and tolerance. THE NEW PHYTOLOGIST 2003; 159:331-340. [PMID: 33873346 DOI: 10.1046/j.1469-8137.2003.00788.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The green alga Chlamydomonas reinhardtii is a useful model of a photosynthetic cell. This unicellular eukaryote has been intensively used for studies of a number of physiological processes such as photosynthesis, respiration, nitrogen assimilation, flagella motility and basal body function. Its easy-to-manipulate and short life cycle make this organism a powerful tool for genetic analysis. Over the past 15 yr, a dramatically increased number of molecular technologies (including nuclear and organellar transformation systems, cosmid, yeast artificial chromosome (YAC) and bacterial artificial chromosome (BAC) libraries, reporter genes, RNA interference, DNA microarrays, etc.) have been applied to Chlamydomonas. Moreover, as parts of the Chlamydomonas genome project, molecular mapping, as well as whole genome and extended expressed sequence tag (EST) sequencing programs, are currently underway. These developments have allowed Chlamydomonas to become an extremely valuable model for molecular approaches to heavy metal homeostasis and tolerance in photosynthetic organisms.
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Affiliation(s)
- M Hanikenne
- Genetics of Microorganisms, Department of Life Sciences, B22, University of Liège, B4000 Liège, Belgium
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