| 1. |
- Christensen, Anna, et al.
(författare)
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Higher plant calreticulins have acquired specialized functions in arabidopsis
- 2010
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 5:6, s. e11342-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Calreticulin (CRT) is a ubiquitous ER protein involved in multiple cellular processes in animals, such as protein folding and calcium homeostasis. Like in animals, plants have evolved divergent CRTs, but their physiological functions are less understood. Arabidopsis contains three CRT proteins, where the two CRTs AtCRT1a and CRT1b represent one subgroup, and AtCRT3 a divergent member. Methodology/Principal Findings: Through expression of single Arabidopsis family members in CRT-deficient mouse fibroblasts we show that both subgroups have retained basic CRT functions, including ER Ca2+-holding potential and putative chaperone capabilities. However, other more general cellular defects due to the absence of CRT in the fibroblasts, such as cell adhesion deficiencies, were not fully restored. Furthermore, in planta expression, protein localization and mutant analyses revealed that the three Arabidopsis CRTs have acquired specialized functions. The AtCRT1a and CRT1b family members appear to be components of a general ER chaperone network. In contrast, and as recently shown, AtCRT3 is associated with immune responses, and is essential for responsiveness to the bacterial Pathogen-Associated Molecular Pattern (PAMP) elf18, derived from elongation factor (EF)-Tu. Whereas constitutively expressed AtCRT1a fully complemented Atcrt1b mutants, AtCRT3 did not. Conclusions/Significance: We conclude that the physiological functions of the two CRT subgroups in Arabidopsis have diverged, resulting in a role for AtCRT3 in PAMP associated responses, and possibly more general chaperone functions for AtCRT1a and CRT1b.
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| 2. |
- Mikami, Koji, et al.
(författare)
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A dibasic amino acid pair conserved in the activation loop directs plasma membrane localization and is necessary for activity of plant type I/II Phosphatidylinositol Phosphate Kinase
- 2010
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 153:3, s. 1004-1015
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Tidskriftsartikel (refereegranskat)abstract
- Phosphatidylinositol phosphate kinase (PIPK) is an enzyme involved in the regulation of cellular levels of phosphoinositides involved in various physiological processes, such as cytoskeletal organization, ion channel activation, and vesicle trafficking. In animals, research has focused on the modes of activation and function of PIPKs, providing an understanding of the importance of plasma membrane localization. However, it still remains unclear how this issue is regulated in plant PIPKs. Here, we demonstrate that the carboxyl-terminal catalytic domain, which contains the activation loop, is sufficient for plasma membrane localization of PpPIPK1, a type I/II B PIPK from the moss Physcomitrella patens. The importance of the carboxyl-terminal catalytic domain for plasma membrane localization was confirmed with Arabidopsis (Arabidopsis thaliana) AtPIP5K1. Our findings, in which substitution of a conserved dibasic amino acid pair in the activation loop of PpPIPK1 completely prevented plasma membrane targeting and abolished enzymatic activity, demonstrate its critical role in these processes. Placing our results in the context of studies of eukaryotic PIPKs led us to conclude that the function of the dibasic amino acid pair in the activation loop in type I/II PIPKs is plant specific.
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| 3. |
- Mikami, Koji, et al.
(författare)
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Is membrane occupation and recognition nexus domain functional in plant phosphatidylinositol phosphate kinases?
- 2010
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Ingår i: Plant Signalling & Behavior. - : Landes Bioscience. - 1559-2316 .- 1559-2324. ; 5:10, s. 1241-1244
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Tidskriftsartikel (refereegranskat)abstract
- Phosphatidylinositol phosphate kinase (PIPK) catalyzes a key step controlling cellular contents of phosphatidylinositol- 4,5-bisphosphate [PtdIns(4,5)P2], a critical intracellular messenger involved in vesicle trafficking and modulation of actin cytoskeleton and also a substrate of phospholipase C to produce the two intracellular messengers, diacylglycerol and inositol-1,4,5-trisphosphate. In addition to the conserved C-terminal PIPK catalytic domain, plant PIPKs contain a unique structural feature consisting of a repeat of membrane occupation and recognition nexus (MORN) motifs, called the MORN domain, in the N-terminal half. The MORN domain has previously been proposed to regulate plasma membrane localization and phosphatidic acid (PA)-inducible activation. Recently, the importance of the catalytic domain, but not the MORN domain, in these aspects was demonstrated. These conflicting data raise the question about the function of the MORN domain in plant PIPKs. We therefore performed analyses of PpPIPK1 from the moss Physcomitrella patens to elucidate the importance of the MORN domain in the control of enzymatic activity; however, we found no effect on either enzymatic activity or activation by PA. Taken together with our previous findings of lack of function in plasma membrane localization, there is no positive evidence indicating roles of the MORN domain in enzymatic and functional regulations of PpPIPK1. Therefore, further biochemical and reverse genetic analyses are necessary to understand the biological significance of the MORN domain in plant PIPKs.
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| 4. |
- Ossipova, Elena, et al.
(författare)
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Affinity purified anti-citrullinated protein/peptide antibodies target antigens expressed in the rheumatoid joint
- 2014
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Ingår i: Arthritis Research & Therapy. - London : BioMed Central (BMC). - 1478-6362 .- 1478-6354. ; 16:4
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: A major subset of patients with rheumatoid arthritis (RA) is characterized by the presence of circulating autoantibodies directed to citrullinated proteins/peptides (ACPAs). These autoantibodies, which are commonly detected by using an enzyme-linked immunosorbent assay (ELISA) based on synthetic cyclic citrullinated peptides (CCPs), predict clinical onset and a destructive disease course. In the present study, we have used plasma and synovial fluids from patients with RA, for the affinity purification and characterization of anti-CCP2 reactive antibodies, with an aim to generate molecular tools that can be used in vitro and in vivo for future investigations into the pathobiology of the ACPA response. Specifically, this study aims to demonstrate that the surrogate marker CCP2 can capture ACPAs that bind to autoantigens expressed in vivo in the major inflammatory lesions of RA (that is, in the rheumatoid joint). METHODS: Plasma (n = 16) and synovial fluid (n = 26) samples were collected from RA patients with anti-CCP2 IgG levels of above 300 AU/mL. Total IgG was isolated on Protein G columns and subsequently applied to CCP2 affinity columns. Purified anti-CCP2 IgG was analyzed for reactivity and specificity by using the CCPlus(R) ELISA, in-house peptide ELISAs, Western blot, and immunohisto-/immunocytochemistry. RESULTS: Approximately 2% of the total IgG pool in both plasma and synovial fluid was CCP2-reactive. Purified anti-CCP2 reactive antibodies from different patients showed differences in binding to CCP2 and differences in binding to citrullinated peptides from alpha-enolase, vimentin, fibrinogen, and collagen type II, illustrating different ACPA fine-specificity profiles. Furthermore, the purified ACPA bound not only in vitro citrullinated proteins but, more importantly, in vivo-generated epitopes on synovial fluid cells and synovial tissues from patients with RA. CONCLUSIONS: We have isolated ACPAs from plasma and synovial fluid and demonstrated that the CCP2 peptides, frequently used in diagnostic ELISAs, de facto act as surrogate antigens for at least four different, well-characterized, largely non-cross-reactive, ACPA fine specificities. Moreover, we have determined the concentration and proportion of CCP2-reactive IgG molecules in rheumatoid plasma and synovial fluid, and we have shown that the purified ACPAs can be used to detect both in vitro- and in vivo-generated citrullinated epitopes by various techniques. We anticipate that these antibodies will provide us with new opportunities to investigate the potential pathogenic effects of human ACPAs. © 2014 Ossipova et al.; licensee BioMed Central Ltd.
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| 5. |
- Saavedra, Laura, et al.
(författare)
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PIP kinases and their role in plant tip growing cells
- 2012
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Ingår i: Plant Signalling & Behavior. - : Taylor & Francis. - 1559-2316 .- 1559-2324. ; 7:10, s. 1302-1305
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Forskningsöversikt (refereegranskat)abstract
- Phosphatidylinositol (4,5) bisphosphate, [PtdIns(4,5)P2], is a signaling lipid involved in many important processes in animal cells such as cytoskeleton organization, intracellular vesicular trafficking, secretion, cell motility, regulation of ion channels, and nuclear signaling pathways. In the last years PtdIns(4,5)P2 and its synthesizing enzyme, phosphatidylinositol phosphate kinase (PIPK), has been intensively studied in plant cells, revealing a key role in the control of polar tip growth. Analysis of the PIPK members from Arabidopsis thaliana, Oryza sativa and Physcomitrella patens showed that they share some regulatory features with animal PIPKs but also exert plant-specific modes of regulation. This review aims at giving an overview on the PIPK family from Arabidopsis thaliana and Physcomitrella patens. Even though their basic structure, modes of activation and physiological role is evolutionary conserved, modules responsible for plasma membrane localization are distinct for different PIPKs, depending on differences in physiological and/ or developmental status of cells, such as polarized and nonpolarized.
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| 6. |
- Saavedra, Laura, et al.
(författare)
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PIPKs are essential for rhizoid elongation and caulonemal cell development in the moss Physcomitrella patens
- 2011
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Ingår i: The Plant Journal. - 0960-7412 .- 1365-313X. ; 67:4, s. 635-647
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Tidskriftsartikel (refereegranskat)abstract
- PtdIns-4,5-bisphosphate is a lipid messenger of eukaryotic cells that plays a critical role in processes such as cytoskeleton organization, intracellular vesicular trafficking, secretion, cell motility, regulation of ion channels and nuclear signalling pathways. The enzymes responsible for the synthesis of PtdIns(4,5)P(2) are phosphatidylinositol phosphate kinases (PIPKs). The moss Physcomitrella patens contains two PIPKs, PpPIPK1 and PpPIPK2. To study their physiological role, both genes were disrupted by targeted homologous recombination and as a result mutant plants with lower PtdIns(4,5)P(2) levels were obtained. A strong phenotype for pipk1, but not for pipk2 single knockout lines, was obtained. The pipk1 knockout lines were impaired in rhizoid and caulonemal cell elongation, whereas pipk1-2 double knockout lines showed dramatic defects in protonemal and gametophore morphology manifested by the absence of rapidly elongating caulonemal cells in the protonemal tissue, leafy gametophores with very short rhizoids, and loss of sporophyte production. pipk1 complemented by overexpression of PpPIPK1 fully restored the wild-type phenotype whereas overexpression of the inactive PpPIPK1E885A did not. Overexpression of PpPIPK2 in the pipk1-2 double knockout did not restore the wild-type phenotype demonstrating that PpPIPK1 and PpPIPK2 are not functionally redundant. In vivo imaging of the cytoskeleton network revealed that the shortened caulonemal cells in the pipk1 mutants was the result of the absence of the apicobasal gradient of cortical F-actin cables normally observed in wild-type caulonemal cells. Our data indicate that both PpPIPKs play a crucial role in the development of the moss P. patens, and particularly in the regulation of tip growth.
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| 7. |
- Sun, Wenjun J., et al.
(författare)
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Calcium efflux of plasma membrane vesicles exposed to ELF magnetic fieldsutest of a nuclear magnetic resonance interaction model
- 2012
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Ingår i: Bioelectromagnetics. - : Wiley. - 0197-8462. ; 33:7, s. 535-542
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Tidskriftsartikel (refereegranskat)abstract
- The question whether very weak, low frequency magnetic fields can affect biological matter is still under debate. The theoretical possibility of such an interaction is often questioned and the site of interaction in the cell is unknown. In the present study, the influence of extremely weak 60?Hz magnetic fields on the transport of Ca2+ was studied in a biological system consisting of highly purified plasma membrane vesicles. We tested a newly proposed quantum mechanical model postulates that polarization of hydrogen nuclei can elicit a biological effect. Vesicles were exposed for half an hour at 32?degrees C and the calcium efflux was studied using radioactive 45Ca2+ as a tracer. A static magnetic field of 26?mu T and time-varying magnetic fields with a frequency of 60?Hz and amplitudes between 0.6 and 6.3?mu T were used. The predictions of the model, proposed by Lednev, that at a frequency of 60?Hz the biological effect under investigation would significantly be altered at the amplitudes of 1.3 and 3.9?mu T could not be confirmed. Bioelectromagnetics 33:535542, 2012. (c) 2012 Wiley Periodicals, Inc.
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| 8. |
- Thelin, Lisa, et al.
(författare)
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Diverging functions among calreticulin isoforms in higher plants
- 2011
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Ingår i: Plant Signalling & Behavior. - : Taylor & Francis. - 1559-2316 .- 1559-2324. ; 6:6, s. 905-910
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The ER chaperone calreticulin plays vital roles in numerous cellular processes, including Ca2+-homeostasis, apoptosis and cell adhesion, in animal cells. Although calreticulin has been systematically characterized in animal cells, the focus has been on one of the isoforms. However, recent advances in the plant calreticulin field have revealed functional divergence of calreticulin isoforms. While two of the plant isoforms appear to work within a general ER chaperone framework, the third isoform is associated with folding of receptors for brassinosteroids and bacterial peptides. Hence, the discovery of functional specialization of plant calreticulins opens up new vistas for calreticulins also in the animal field.
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