| 41481. |
- Kleczkowski, Leszek A., 1954-, et al.
(författare)
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Magnesium and cell energetics : at the junction of metabolism of adenylate and non-adenylate nucleotides
- 2023
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Ingår i: Journal of plant physiology (Print). - : Elsevier. - 0176-1617 .- 1618-1328. ; 280
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Tidskriftsartikel (refereegranskat)abstract
- Free magnesium (Mg2+) represents a powerful signal arising from interconversions of adenylates (ATP, ADP and AMP). This is a consequence of the involvement of adenylate kinase (AK) which equilibrates adenylates and uses defined species of Mg-complexed and Mg-free adenylates in both directions of its reaction. However, cells contain also other reversible Mg2+-dependent enzymes that equilibrate non-adenylate nucleotides (uridylates, cytidylates and guanylates), i.e. nucleoside monophosphate kinases (NMPKs) and nucleoside diphosphate kinase (NDPK). Here, we propose that AK activity is tightly coupled to activities of NMPK and NDPK, linking adenylate equilibrium to equilibria of other nucleotides, and with [Mg2+] controlling the ratios of Mg-chelated and Mg-free nucleotides. This coupling establishes main hubs for adenylate-driven equilibration of non-adenylate nucleotides, with [Mg2+] acting as signal arising from all nucleotides rather than adenylates only. Further consequences involve an overall adenylate control of UTP-, GTP- and CTP-dependent pathways and the availability of substrates for RNA and DNA synthesis.
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| 41482. |
- Kleczkowski, Leszek A., 1954-, et al.
(författare)
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Magnesium signaling in plants
- 2021
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Ingår i: International Journal of Molecular Sciences. - : MPDI. - 1661-6596 .- 1422-0067. ; 22:3
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Forskningsöversikt (refereegranskat)abstract
- Free magnesium (Mg2+) is a signal of the adenylate (ATP+ADP+AMP) status in the cells. It results from the equilibrium of adenylate kinase (AK), which uses Mg-chelated and Mgfree adenylates as substrates in both directions of its reaction. The AK-mediated primary control of intracellular [Mg2+] is finely interwoven with the operation of membrane-bound adenylateand Mg2+-translocators, which in a given compartment control the supply of free adenylates and Mg2+ for the AK-mediated equilibration. As a result, [Mg2+] itself varies both between and within the compartments, depending on their energetic status and environmental clues. Other key nucleotide-utilizing/producing enzymes (e.g., nucleoside diphosphate kinase) may also be involved in fine-tuning of the intracellular [Mg2+]. Changes in [Mg2+] regulate activities of myriads of Mgutilizing/ requiring enzymes, affecting metabolism under both normal and stress conditions, and impacting photosynthetic performance, respiration, phloem loading and other processes. In compartments controlled by AK equilibrium (cytosol, chloroplasts, mitochondria, nucleus), the intracellular [Mg2+] can be calculated from total adenylate contents, based on the dependence of the apparent equilibrium constant of AK on [Mg2+]. Magnesium signaling, reflecting cellular adenylate status, is likely widespread in all eukaryotic and prokaryotic organisms, due simply to the omnipresent nature of AK and to its involvement in adenylate equilibration.
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| 41483. |
- Kleczkowski, Leszek A, 1954-, et al.
(författare)
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Mechanisms of UDP-glucose synthesis in plants
- 2010
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Ingår i: Critical reviews in plant sciences. - : Informa UK Limited. - 0735-2689 .- 1549-7836. ; 29:4, s. 191-203
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Tidskriftsartikel (refereegranskat)abstract
- Substantial progress has been made in studies on enzymes synthesizing UDP-glucose (UDPG) which is essential for sucrose and cell wall biosynthesis, and in an array of other processes, e.g. glycosylation of proteins and lipids. The enzymes include UDPG pyrophosphorylase, UDP-sugar pyrophosphorylase (USPase) and sucrose synthase (SuSy). Genes coding for those proteins are under complex spatial and temporal regulation, and are frequently coexpressed. Recent evidence for regulation of some of the UDPG-synthesizing proteins by posttranslational modifications and oligomerization, together with discoveries of novel isozymes and unexpected locations within a cell (including chloroplasts and mitochondria) have made the studies exciting, but complex. The enzymes differ in specificity for sugar and nucleotide portions of their substrates/products, and may be involved in distinct metabolic pathways, but also in signaling. Homology models for USPase and SuSy structures are presented, based on recent crystallization of structurally related proteins. Future challenges in research on UDPG-producing enzymes are underlined.
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| 41484. |
- Kleczkowski, Leszek A, 1954-, et al.
(författare)
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Molecular cloning and spatial expression of an ApL1 cDNA for the large subunit of ADP-glucose pyrophosphorylase from Arabidopsis thaliana
- 1999
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Ingår i: Zeitschrift für Naturforschung C - A Journal of Biosciences. - 0939-5075 .- 1865-7125. ; 54:5-6, s. 353-358
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Tidskriftsartikel (refereegranskat)abstract
- A cDNA, ApL1a, corresponding to a homologue of the large subunit of ADP-glucose pyrophosphorylase (AGPase), has been isolated/characterised by screening a cDNA library prepared from leaves of Arabidopsis thaliana, followed by rapid amplification of cDNA 3'-ends (3'-RACE). Within the 1685 nucleotide-long sequence (excluding polyA tail), an open reading frame encodes a protein of 522 amino acids (aa), with a calculated molecular weight of 57.7 kDa. The derived aa sequence does not contain any discernible transit peptide cleavage site motif, similarly to two other recently sequenced full-length Arabidopsis homologues for AGPase, and shows ca. 58-78% identity to homologous proteins from other plants/tissues. The corresponding gene was found to be expressed in all tissues examined (rosette and stem leaves, stems, flowers and fruits). The ubiquitous expression of the gene is consistent with its critical role in starch synthesis in Arabidopsis.
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| 41485. |
- Kleczkowski, Leszek A., 1954-, et al.
(författare)
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Multiple roles of glycerate kinase—from photorespiration to gluconeogenesis, C4 metabolism, and plant immunity
- 2024
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Ingår i: International Journal of Molecular Sciences. - : MDPI. - 1661-6596 .- 1422-0067. ; 25:6
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Forskningsöversikt (refereegranskat)abstract
- Plant glycerate kinase (GK) was previously considered an exclusively chloroplastic enzyme of the glycolate pathway (photorespiration), and its sole predicted role was to return most of the glycolate-derived carbon (as glycerate) to the Calvin cycle. However, recent discovery of cytosolic GK revealed metabolic links for glycerate to other processes. Although GK was initially proposed as being solely regulated by substrate availability, subsequent discoveries of its redox regulation and the light involvement in the production of chloroplastic and cytosolic GK isoforms have indicated a more refined regulation of the pathways of glycerate conversion. Here, we re-evaluate the importance of GK and emphasize its multifaceted role in plants. Thus, GK can be a major player in several branches of primary metabolism, including the glycolate pathway, gluconeogenesis, glycolysis, and C4 metabolism. In addition, recently, the chloroplastic (but not cytosolic) GK isoform was implicated as part of a light-dependent plant immune response to pathogen attack. The origins of glycerate are also discussed here; it is produced in several cell compartments and undergoes huge fluctuations depending on light/dark conditions. The recent discovery of the vacuolar glycerate transporter adds yet another layer to our understanding of glycerate transport/metabolism and that of other two- and three-carbon metabolites.
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| 41486. |
- Kleczkowski, Leszek A., 1954-, et al.
(författare)
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Optimization of nucleotide sugar supply for polysaccharide formation via thermodynamic buffering
- 2020
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Ingår i: Biochemical Journal. - : Portland Press. - 0264-6021 .- 1470-8728. ; 477:2, s. 341-356
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Tidskriftsartikel (refereegranskat)abstract
- Plant polysaccharides (cellulose, hemicellulose, pectin, starch) are either direct (i.e. leaf starch) or indirect products of photosynthesis, and they belong to the most abundant organic compounds in nature. Although each of these polymers is made by a specific enzymatic machinery, frequently in different cell locations, details of their synthesis share certain common features. Thus, the production of these polysaccharides is preceded by the formation of nucleotide sugars catalyzed by fully reversible reactions of various enzymes, mostly pyrophosphorylases. These 'buffering' enzymes are, generally, quite active and operate close to equilibrium. The nucleotide sugars are then used as substrates for irreversible reactions of various polysaccharide-synthesizing glycosyltransferases ('engine' enzymes), e.g. plastidial starch synthases, or plasma membrane-bound cellulose synthase and callose synthase, or ER/Golgi-located variety of glycosyltransferases forming hemicellulose and pectin backbones. Alternatively, the irreversible step might also be provided by a carrier transporting a given immediate precursor across a membrane. Here, we argue that local equilibria, established within metabolic pathways and cycles resulting in polysaccharide production, bring stability to the system via the arrangement of a flexible supply of nucleotide sugars. This metabolic system is itself under control of adenylate kinase and nucleoside-diphosphate kinase, which determine the availability of nucleotides (adenylates, uridylates, guanylates and cytidylates) and Mg2+, the latter serving as a feedback signal from the nucleotide metabolome. Under these conditions, the supply of nucleotide sugars to engine enzymes is stable and constant, and the metabolic process becomes optimized in its load and consumption, making the system steady and self-regulated.
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| 41487. |
- Kleczkowski, Leszek A., 1954-, et al.
(författare)
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Sugar activation for production of nucleotide sugars as aubstrates for glycosyltransferases in plants
- 2015
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Ingår i: Journal of Applied Glycoscience. - Tokyo : The Japanese Society of Applied Glycoscience. - 1344-7882 .- 1880-7291. ; 62:2, s. 25-36
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Forskningsöversikt (refereegranskat)abstract
- In order to serve as a glycosyl donor, a sugar or a sugar derivative (e.g. GlcA) needs to be “activated” to a highly energetic state of a nucleotide-sugar. This activation requires the involvement of specific enzymes which produce NDP-sugars (or, in one case, NMP-sugar), using NTP or NDP as substrate. The present review provides concise survey of distinct plant nucleotide-sugar pyrophosphorylases (all using NTP as one of the substrates and differing in sugar specificity) as well as nucleotide-sugar phosphorylases and sucrose synthase (all using NDP as one of substrates). The pyrophosphorylases discussed include UGPase, USPase, UAGPase, AGPase, GMPase (VTC1), and FKGP, whereas phosphorylases include ADP-Glc phosphorylase and GDP-Gal phosphorylase (VTC2/VTC5). We also discuss the activation mechanism of 3-deoxy-D-manno-octulosonic acid (Kdo) by CKS, leading to the formation of a unique NMP-linked sugar (CMP-Kdo).
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| 41488. |
- Kleczkowski, Leszek A, 1954-, et al.
(författare)
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UDP-sugar pyrophosphorylase : a new old mechanism for sugar activation
- 2011
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 156:1, s. 3-10
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments in studies on properties and functions of UDP-sugar pyrophosphorylase (USPase) in metabolism are presented. The protein was characterized from plants and protozoans (Leishmania, Trypanosoma), but apparently it is also present in bacteria. In plants, USPase deficiency leads to male-sterility. USPase produces a variety of UDP-sugars and their analogs required for cell wall biosynthesis as well as for protein and lipid glycosylation, among other functions. Substrate specificity of USPases from different sources is reviewed, and their function/ structure properties are discussed, based on recent crystallization of the protein, with emphasis on common structural blueprint with some other pyrophosphorylases. Some strategies for future research on USPase are discussed.
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| 41489. |
- Kleczkowski, Leszek, et al.
(författare)
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Factors affecting oligomerization status of UDP-glucose pyrophosphorylase.
- 2005
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Ingår i: Phytochemistry. - : Elsevier BV. - 0031-9422. ; 66:24, s. 2815-21
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Tidskriftsartikel (refereegranskat)abstract
- UDP-glucose pyrophosphorylase (UGPase) is involved in the production of UDP-glucose, a key precursor to polysaccharide synthesis in all organisms. UGPase activity has recently been proposed to be regulated by oligomerization, with monomer as the active species. In the present study, we investigated factors affecting oligomerization status of the enzyme, using purified recombinant barley UGPase. Incubation of wild-type (wt) UGPase with phosphate or Tris buffers promoted oligomerization, whereas Mops and Hepes completely dissociated the oligomers to monomers (the active form). Similar buffer effects were observed for KK127-128LL and C99S mutants of UGPase; however, the buffers had a relatively small effect on the oligomerization status of the LIV135-137NIN mutant, impaired in deoligomerization ability and showing only 6–9% activity of the wt. Buffer composition had no effect on UGPase activity at UGPase protein concentrations below ca. 20 ng/ml. However, at higher protein concentration the activity in Tris, but not Mops nor Hepes, underestimated the amount of the enzyme. The data suggest that oligomerization status of UGPase can be controlled by subtle changes in an immediate environment (buffers) and by protein dilution. The evidence is discussed in relation to our recent model of UGPase structure/function, and with respect to earlier reports on the oligomeric integrity/activity of UGPases from eukaryotic tissues.
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| 41490. |
- Kleczkowski, Leszek, et al.
(författare)
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UDP-glucose pyrophosphorylase. An old protein with new tricks.
- 2004
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 134:3, s. 912-8
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Tidskriftsartikel (refereegranskat)abstract
- Sugars are central to a plant's raison d'etre as products of photosynthesis. They are the ultimate source of energy and carbon skeletons for all biomolecules, and they provide the material out of which a plant builds its cell walls, fibers, and wood. Thus, regulation of any activity involved in biosynthesis of sugars, especially Suc (the major transport form of carbon in plants), is of utmost interest in understanding the growth and development strategies of a plant. Sugars are also potent regulators of gene expression, via e.g. a hexokinase (HXK) transduction mechanism that senses hexoses, or via Suc-specific or osmoticum transduction pathways, further underlying the importance of sugars in plant homeostasis.
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