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Query: EC:2.4.1.14 (SPS)
 813 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Sucrose-phosphate synthase (SPS; E.C. 2.4.1.14) is the plant enzyme thought to play a major role in sucrose biosynthesis. In photosynthetic and nonphotosynthetic tissues, SPS is regulated by metabolites and by reversible protein phosphorylation. In leaves, phosphorylation modulates SPS activity in response to light/dark signals and end-product accumulation. SPS is phosphorylated on multiple seryl residues in vivo, and the major regulatory phosphorylation site involved is Ser158 in spinach leaves and Ser162 in maize leaves. Regulation of the enzymatic activity of SPS appears to involve calcium, metabolites, and novel "coarse" control of the protein phosphatase that activates SPS. Activation of SPS also occurs during osmotic stress of leaf tissue in darkness, which may function to facilitate sucrose formation for osmoregulation. Manipulation of SPS expression in vivo confirms the role of this enzyme in the control of sucrose biosynthesis.
Annu Rev Plant Physiol Plant Mol Biol 1996 Jun
PMID:ROLE AND REGULATION OF SUCROSE-PHOSPHATE SYNTHASE IN HIGHER PLANTS. 1501 96

SCFGrr1, one of several members of the SCF family of E3 ubiquitin ligases in budding Saccharomyces cerevisiae, is required for both regulation of the cell cycle and nutritionally controlled transcription. In addition to its role in degradation of Gic2 and the CDK targets Cln1 and Cln2, Grr1 is also required for induction of glucose- and amino acid-regulated genes. Induction of HXT genes by glucose requires the Grr1-dependent degradation of Mth1. We show that Mth1 is ubiquitinated in vivo and degraded via the proteasome. Furthermore, phosphorylated Mth1, targeted by the casein kinases Yck1/2, binds to Grr1. That binding depends upon the Grr1 leucine-rich repeat (LRR) domain but not upon the F-box or basic residues within the LRR that are required for recognition of Cln2 and Gic2. Those observations extend to a large number of Grr1-dependent genes, some targets of the amino acid-regulated SPS signaling system, which are properly regulated in the absence of those basic LRR residues. Finally, we show that regulation of the SPS targets requires the Yck1/2 casein kinases. We propose that casein kinase I plays a similar role in both nutritional signaling pathways by phosphorylating pathway components and targeting them for ubiquitination by SCFGrr1.
Mol Cell Biol 2004 Oct
PMID:Regulation and recognition of SCFGrr1 targets in the glucose and amino acid signaling pathways. 1545 73

The constitutive cytosolic expression of a yeast ( Saccharomyces cerevisiae ) invertase within potato ( Solanum tuberosum ) tubers has previously been documented to produce a dramatic metabolic phenotype in which glycolysis, respiration and amino acid synthesis are markedly enhanced at the cost of starch synthesis. These transgenic lines were further characterised by a massive cycle of sucrose degradation and resynthesis via sucrose-phosphate synthase. We have recently developed a B33 patatin driven alc gene construct allowing tight chemical control of gene expression following supply of acetaldehyde with minimal pleiotropic effects of the inducing agent on metabolism. This construct was used for chemical induction of the yeast invertase gene after 10-weeks growth to dissect the complex metabolic phenotype obtained after constitute expression. Inducible expression led to increased invertase activity within 24 h in well-defined areas within growing tubers. Although the sucrose levels were reduced, there was no effect on the levels of starch whilst levels of many amino acids decreased. Labelling experiments revealed that these lines exhibited increased rates of sucrose cycling, whereas rates of glycolysis and of starch synthesis were not substantially changed. From these results we conclude that sucrose cycling is stimulated in response to a short-term increase in the rate of sucrose mobilisation, providing evidence for a role of sucrose cycling as a buffering capacity that regulates the net rate of sucrose usage. In contrast, the dramatic increase in hexose-phosphate levels and the switch from starch synthesis to respiration seen on the constitutive expression of the invertase was not observed in the inducible lines, suggesting that this is the result of cumulative pleiotropic effects that occurred when the transgene was expressed throughout development.
Plant Mol Biol 2004 Sep
PMID:Temporally regulated expression of a yeast invertase in potato tubers allows dissection of the complex metabolic phenotype obtained following its constitutive expression. 1560 30

Prior data indicated that enhanced availability of sucrose, a major product of photosynthesis in source leaves and the carbon source for secondary wall cellulose synthesis in fiber sinks, might improve fiber quality under abiotic stress conditions. To test this hypothesis, a family of transgenic cotton plants (Gossypium hirsutum cv. Coker 312 elite) was produced that over-expressed spinach sucrose-phosphate synthase (SPS) because of its role in regulation of sucrose synthesis in photosynthetic and heterotrophic tissues. A family of 12 independent transgenic lines was characterized in terms of foreign gene insertion, expression of spinach SPS, production of spinach SPS protein, and development of enhanced extractable V (max) SPS activity in leaf and fiber. Lines with the highest V (max) SPS activity were further characterized in terms of carbon partitioning and fiber quality compared to wild-type and transgenic null controls. Leaves of transgenic SPS over-expressing lines showed higher sucrose:starch ratio and partitioning of (14)C to sucrose in preference to starch. In two growth chamber experiments with cool nights, ambient CO(2) concentration, and limited light below the canopy, the transgenic line with the highest SPS activity in leaf and fiber had higher fiber micronaire and maturity ratio associated with greater thickness of the cellulosic secondary wall.
Plant Mol Biol 2007 Apr
PMID:Transgenic cotton over-producing spinach sucrose phosphate synthase showed enhanced leaf sucrose synthesis and improved fiber quality under controlled environmental conditions. 1728 85

Cells of the budding yeast Saccharomyces cerevisiae sense extracellular amino acids and activate expression of amino acid permeases through the SPS-sensing pathway, which consists of Ssy1, an amino acid sensor on the plasma membrane, and two downstream factors, Ptr3 and Ssy5. Upon activation of SPS signaling, two transcription factors, Stp1 and Stp2, undergo Ssy5-dependent proteolytic processing that enables their nuclear translocation. Here we show that Ptr3 is a phosphoprotein whose hyperphosphorylation is increased by external amino acids and is dependent on Ssy1 but not on Ssy5. A deletion mutation in GRR1, encoding a component of the SCF(Grr1) E3 ubiquitin ligase, blocks amino acid-induced hyperphosphorylation of Ptr3. We found that two casein kinase I (CKI) proteins, Yck1 and Yck2, previously identified as positive regulators of SPS signaling, are required for hyperphosphorylation of Ptr3. Loss- and gain-of-function mutations in PTR3 result in decreased and increased Ptr3 hyperphosporylation, respectively. We found that a defect in PP2A phosphatase activity leads to the hyperphosphorylation of Ptr3 and constitutive activation of SPS signaling. Two-hybrid analysis revealed interactions between the N-terminal signal transduction domain of Ssy1 with Ptr3 and Yck1. Our findings reveal that CKI and PP2A phosphatase play antagonistic roles in SPS sensing by regulating Ptr3 phosphorylation.
Mol Cell Biol 2008 Jan
PMID:Activation of the SPS amino acid-sensing pathway in Saccharomyces cerevisiae correlates with the phosphorylation state of a sensor component, Ptr3. 1798 23

Upon stimulation, many proteins translocate into the nucleus in order to regulate a variety of cellular processes. The mechanism underlying the translocation is not clear since many of these proteins lack a canonical nuclear localization signal (NLS). We searched for an alternative mechanism in extracellular signal-regulated kinase (ERK)-2 and identified a 3 amino acid domain (SPS) that is phosphorylated upon stimulation to induce nuclear translocation of ERK2. A 19 amino acid stretch containing this phosphorylated domain inserts nondiffusible proteins to the nucleus autonomously. The phosphorylated SPS acts by binding to importin7 and the release from nuclear pore proteins. This allows its functioning both in passive and active ERK transports. A similar domain appears in many cytonuclear shuttling proteins, and we found that phosphorylation of similar sequences in SMAD3 or MEK1 also induces their nuclear accumulation. Therefore, our findings show that this phosphorylated domain acts as a general nuclear translocation signal (NTS).
Mol Cell 2008 Sep 26
PMID:Identification and characterization of a general nuclear translocation signal in signaling proteins. 1876 Sep 48

The effect of over-expression of AtDREB1A gene in chrysanthemums on heat stress tolerance was investigated. Transgenic plants with 35S:AtDREB1A construct (henceforth, 35S plants) and wild type (WT) plants were exposed to 45 degrees C as a heat stress treatment. When heat-treated for 36 h and followed by a 3-week recovery, approximately 70% of the 35S plants, but less than 20% of the WT plants were survived. Leaf electrolyte leakage was significantly lower in 35S plants than in WT plants. cDNA macroarray analysis showed that 55 of 74 DREB1A regulon members were up-regulated under heat stress in WT plants. In comparison with WT plants, 35S plants displayed greatly enhanced expression of the genes including signal transduction, transcription and HSP70 in the early time, and the genes including photosynthesis and metabolism in the late time of the heat treatment. We also found that the 35S plants maintained significantly higher photosynthetic capacity, and elevated activity of Rubisco and sucrose-phosphate synthase under heat stress. These results suggest that improvement of heat stress tolerance in transgenic chrysanthemum may be associated with enhanced tolerance of photosynthesis.
Plant Mol Biol 2009 Jun
PMID:Over-expression of AtDREB1A in chrysanthemum enhances tolerance to heat stress. 1923 75

Extracellular amino acids induce the yeast SPS sensor to endoproteolytically cleave transcription factors Stp1 and Stp2 in a process termed receptor-activated proteolysis (RAP). Ssy5, the activating endoprotease, is synthesized with a large N-terminal prodomain and a C-terminal chymotrypsin-like catalytic (Cat) domain. During biogenesis, Ssy5 cleaves itself and the prodomain and Cat domain remain associated, forming an inactive primed protease. Here we show that the prodomain is a potent inhibitor of Cat domain activity and that its inactivation is a requisite for RAP. Accordingly, amino acid-induced signals trigger proteasome-dependent degradation of the prodomain. A mutation that stabilizes the prodomain prevents Stp1 processing, whereas destabilizing mutations lead to constitutive RAP-independent Stp1 processing. We fused a conditional degron to the prodomain to synthetically reprogram the amino acid-responsive SPS signaling pathway, placing it under temperature control. Our results define a regulatory mechanism that is novel for eukaryotic proteases functioning within cells.
Mol Cell Biol 2010 Jul
PMID:The prodomain of Ssy5 protease controls receptor-activated proteolysis of transcription factor Stp1. 2042 14

Regulated proteolysis serves as a mechanism to control cellular processes. The SPS (Ssy1-Ptr3-Ssy5) sensor in yeast responds to extracellular amino acids by endoproteolytically activating transcription factors Stp1 and Stp2 (Stp1/2). The processing endoprotease Ssy5 is regulated via proteasomal degradation of its noncovalently associated N-terminal prodomain. We find that degradation of the prodomain requires a conserved phosphodegron comprising phosphoacceptor sites and ubiquitin-accepting lysine residues. Upon amino acid induction, the phosphodegron is modified in a series of linked events by a set of general regulatory factors involved in diverse signaling pathways. First, an amino acid-induced conformational change triggers phosphodegron phosphorylation by the constitutively active plasma membrane-localized casein kinase I (Yck1/2). Next the prodomain becomes a substrate for polyubiquitylation by the Skp1/Cullin/Grr1 E3 ubiquitin ligase complex (SCF(Grr1)). Finally, the modified prodomain is concomitantly degraded by the 26S proteasome. These integrated events are requisite for unfettering the Ssy5 endoprotease, and thus Stp1/2 processing. The Ssy5 phosphoacceptor motif resembles the Yck1/2- and Grr1-dependent degrons of regulators in the Snf3/Rgt2 glucose-sensing pathway. Our work defines a novel proteolytic activation cascade that regulates an intracellular signaling protease and illustrates how general signaling components are recruited to distinct pathways that achieve conditional and specific signaling outputs.
Mol Biol Cell 2011 Aug 01
PMID:A phosphodegron controls nutrient-induced proteasomal activation of the signaling protease Ssy5. 2165 27

Nutrient sensing and metabolic reprogramming are crucial for metazoan cell aging and tumor growth. Here, we identify metabolic and regulatory parallels between a layered, multicellular yeast colony and a tumor-affected organism. During development, a yeast colony stratifies into U and L cells occupying the upper and lower colony regions, respectively. U cells activate a unique metabolism controlled by the glutamine-induced TOR pathway, amino acid-sensing systems (SPS and Gcn4p) and signaling from mitochondria with lowered respiration. These systems jointly modulate U cell physiology, which adapts to nutrient limitations and utilize the nutrients released from L cells. Stress-resistant U cells share metabolic pathways and other similar characteristics with tumor cells, including the ability to proliferate. L cells behave similarly to stressed and starving cells, which activate degradative mechanisms to provide nutrients to U cells. Our data suggest a nutrient flow between both cell types, resembling the Cori cycle and glutamine-NH(4)(+) shuttle between tumor and healthy metazoan cells.
Mol Cell 2012 May 25
PMID:Cell differentiation within a yeast colony: metabolic and regulatory parallels with a tumor-affected organism. 2256 Sep 24


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