| 1. |
- Valegård, Karin, et al.
(författare)
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Structural and functional analyses of Rubisco from arctic diatom species reveal unusual posttranslational modifications
- 2018
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 293:34, s. 13033-13043
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic performance of the major CO2-assimilating enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), restricts photosynthetic productivity. Natural diversity in the catalytic properties of Rubisco indicates possibilities for improvement. Oceanic phytoplankton contain some of the most efficient Rubisco enzymes, and diatoms in particular are responsible for a significant proportion of total marine primary production as well as being a major source of CO2 sequestration in polar cold waters. Until now, the biochemical properties and three-dimensional structures of Rubisco from diatoms were unknown. Here, diatoms from arctic waters were collected, cultivated, and analyzed for their CO2-fixing capability. We characterized the kinetic properties of five and determined the crystal structures of four Rubiscos selected for their high CO2-fixing efficiency. The DNA sequences of the rbcL, and rbcS genes of the selected diatoms were similar, reflecting their close phylogenetic relationship. The V-max and K-m for the oxygenase and carboxylase activities at 25 degrees C and the specificity factors (S-c/o) at 15, 25, and 35 degrees C were determined. The S-c/o values were high, approaching those of mono- and dicot plants, thus exhibiting good selectivity for CO(2 )relative to O-2. Structurally, diatom Rubiscos belong to form I C/D, containing small subunits characterized by a short beta A-beta B loop and a C-terminal extension that forms a beta-hairpin structure (beta E-beta F loop). Of note, the diatom Rubiscos featured a number of posttranslational modifications of the large subunit, including 4-hydroxyproline, beta-hydroxyleucine, hydroxylated and nitrosylated cysteine, mono- and dihydroxylated lysine, and trimethylated lysine. Our studies suggest adaptation toward achieving efficient CO2 fixation in arctic diatom Rubiscos.
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| 2. |
- Hsiao, An-Shan, et al.
(författare)
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Arabidopsis cytosolic acyl-CoA-binding proteins ACBP4, ACBP5 and ACBP6 have overlapping but distinct roles in seed development
- 2014
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Ingår i: Bioscience Reports. - 0144-8463 .- 1573-4935. ; 34:6, s. 865-877
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Tidskriftsartikel (refereegranskat)abstract
- Eukaryotic cytosolic ACBPs (acyl-CoA-binding proteins) bind acyl-CoA esters and maintain a cytosolic acyl-CoA pool, but the thermodynamics of their protein-lipid interactions and physiological relevance in plants are not well understood. Arabidopsis has three cytosolic ACBPs which have been identified as AtACBP4, AtACBP5 and AtACBP6, and microarray data indicated that all of them are expressed in seeds; AtACBP4 is expressed in early embryogenesis, whereas AtACBP5 is expressed later. ITC (isothermal titration calorimetry) in combination with transgenic Arabidopsis lines were used to investigate the roles of these three ACBPs from Arabidopsis thaliana. The dissociation constants, stoichiometry and enthalpy change of AtACBP interactions with various acyl-CoA esters were determined using ITC. Strong binding of recombinant (r) AtACBP6 with long-chain acyl-CoA (C16-to C18-CoA) esters was observed with dissociation constants in the nanomolar range. However, the affinity of rAtACBP4 and rAtACBP5 to these acyl-CoA esters was much weaker (dissociation constants in the micromolar range), suggesting that they interact with acyl-CoA esters differently from rAtACBP6. When transgenic Arabidopsis expressing AtACBP6pro::GUS was generated, strong GUS (beta-glucuronidase) expression in cotyledonary-staged embryos and seedlings prompted us to measure the acyl-CoA contents of the acbp6 mutant. This mutant accumulated higher levels of C18:1-CoA and C18:1- and C18:2-CoAs in cotyledonary-staged embryos and seedlings, respectively, in comparison with the wild type. The acbp4acbp5acbp6 mutant showed the lightest seed weight and highest sensitivity to abscisic acid during germination, suggesting their physiological functions in seeds.
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| 3. |
- Talamonti, Emanuela, et al.
(författare)
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Impairment of DHA synthesis alters the expression of neuronal plasticity markers and the brain inflammatory status in mice
- 2020
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Ingår i: The FASEB Journal. - 0892-6638 .- 1530-6860. ; 34:2, s. 2024-2040
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Tidskriftsartikel (refereegranskat)abstract
- Docosahexaenoic acid (DHA) is a omega-3 fatty acid typically obtained from the diet or endogenously synthesized through the action of elongases (ELOVLs) and desaturases. DHA is a key central nervous system constituent and the precursor of several molecules that regulate the resolution of inflammation. In the present study, we questioned whether the impaired synthesis of DHA affected neural plasticity and inflammatory status in the adult brain. To address this question, we investigated neural and inflammatory markers from mice deficient for ELOVL2 (Elovl2(-/-)), the key enzyme in DHA synthesis. From our findings, Elovl2(-/-) mice showed an altered expression of markers involved in synaptic plasticity, learning, and memory formation such as Egr-1, Arc1, and BDNF specifically in the cerebral cortex, impacting behavioral functions only marginally. In parallel, we also found that DHA-deficient mice were characterized by an increased expression of pro-inflammatory molecules, namely TNF, IL-1 beta, iNOS, caspase-1 as well as the activation and morphologic changes of microglia in the absence of any brain injury or disease. Reintroducing DHA in the diet of Elovl2(-/-) mice reversed such alterations in brain plasticity and inflammation. Hence, impairment of systemic DHA synthesis can modify the brain inflammatory and neural plasticity status, supporting the view that DHA is an essential fatty acid with an important role in keeping inflammation within its physiologic boundary and in shaping neuronal functions in the central nervous system.
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