ORCID Profile
0000-0002-8447-7249
Current Organisation
Queen's University
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Publisher: Oxford University Press (OUP)
Date: 09-01-2008
Abstract: The phosphoenolpyruvate carboxylase (PEPC) interactome of developing castor oil seed (COS Ricinus communis) endosperm was assessed using coimmunopurification (co-IP) followed by proteomic analysis. Earlier studies suggested that immunologically unrelated 107-kD plant-type PEPCs (p107/PTPC) and 118-kD bacterial-type PEPCs (p118/BTPC) are subunits of an unusual 910-kD hetero-octameric class 2 PEPC complex of developing COS. The current results confirm that a tight physical interaction occurs between p118 and p107 because p118 quantitatively coimmunopurified with p107 following elution of COS extracts through an anti-p107-IgG immunoaffinity column. No PEPC activity or immunoreactive PEPC polypeptides were detected in the corresponding flow-through fractions. Although BTPCs lack the N-terminal phosphorylation motif characteristic of PTPCs, Pro-Q Diamond phosphoprotein staining, immunoblotting with phospho-serine (Ser)/threonine Akt substrate IgG, and phosphate-affinity PAGE established that coimmunopurified p118 was multiphosphorylated at unique Ser and/or threonine residues. Tandem mass spectrometric analysis of an endoproteinase Lys-C p118 peptide digest demonstrated that Ser-425 is subject to in vivo proline-directed phosphorylation. The co-IP of p118 with p107 did not appear to be influenced by their phosphorylation status. Because p118 phosphorylation was unchanged 48 h following elimination of photosynthate supply due to COS depodding, the signaling mechanisms responsible for photosynthate-dependent p107 phosphorylation differ from those controlling p118's in vivo phosphorylation. A 110-kD PTPC coimmunopurified with p118 and p107 when depodded COS was used. The plastidial pyruvate dehydrogenase complex (PDCpl) was identified as a novel PEPC interactor. Thus, a putative metabolon involving PEPC and PDCpl could function to channel carbon from phosphoenolpyruvate to acetyl-coenzyme A and/or to recycle CO2 from PDCpl to PEPC.
Publisher: Elsevier BV
Date: 09-2009
Publisher: Wiley
Date: 09-03-2012
DOI: 10.1016/J.FEBSLET.2012.02.054
Abstract: Phosphoenolpyruvate carboxylase (PEPC) is a tightly controlled anaplerotic enzyme situated at a pivotal branch point of plant carbohydrate-metabolism. In developing castor oil seeds (COS) a novel allosterically-densensitized 910-kDa Class-2 PEPC hetero-octameric complex arises from a tight interaction between 107-kDa plant-type PEPC and 118-kDa bacterial-type PEPC (BTPC) subunits. Mass spectrometry and immunoblotting with anti-phosphoSer451 specific antibodies established that COS BTPC is in vivo phosphorylated at Ser451, a highly conserved target residue that occurs within an intrinsically disordered region. This phosphorylation was enhanced during COS development or in response to depodding. Kinetic characterization of a phosphomimetic (S451D) mutant indicated that Ser451 phosphorylation inhibits the catalytic activity of BTPC subunits within the Class-2 PEPC complex.
Publisher: Portland Press Ltd.
Date: 27-04-2011
DOI: 10.1042/BJ20110078
Abstract: PEPC [PEP (phosphoenolpyruvate) carboxylase] is a tightly controlled enzyme located at the core of plant C-metabolism that catalyses the irreversible β-carboxylation of PEP to form oxaloacetate and Pi. The critical role of PEPC in assimilating atmospheric CO2 during C4 and Crassulacean acid metabolism photosynthesis has been studied extensively. PEPC also fulfils a broad spectrum of non-photosynthetic functions, particularly the anaplerotic replenishment of tricarboxylic acid cycle intermediates consumed during biosynthesis and nitrogen assimilation. An impressive array of strategies has evolved to co-ordinate in vivo PEPC activity with cellular demands for C4–C6 carboxylic acids. To achieve its erse roles and complex regulation, PEPC belongs to a small multigene family encoding several closely related PTPCs (plant-type PEPCs), along with a distantly related BTPC (bacterial-type PEPC). PTPC genes encode ~110-kDa polypeptides containing conserved serine-phosphorylation and lysine-mono-ubiquitination sites, and typically exist as homotetrameric Class-1 PEPCs. In contrast, BTPC genes encode larger ~117-kDa polypeptides owing to a unique intrinsically disordered domain that mediates BTPC's tight interaction with co-expressed PTPC subunits. This association results in the formation of unusual ~900-kDa Class-2 PEPC hetero-octameric complexes that are desensitized to allosteric effectors. BTPC is a catalytic and regulatory subunit of Class-2 PEPC that is subject to multi-site regulatory phosphorylation in vivo. The interaction between ergent PEPC polypeptides within Class-2 PEPCs adds another layer of complexity to the evolution, physiological functions and metabolic control of this essential CO2-fixing plant enzyme. The present review summarizes exciting developments concerning the functions, post-translational controls and subcellular location of plant PTPC and BTPC isoenzymes.
Publisher: Oxford University Press (OUP)
Date: 12-08-2011
DOI: 10.1093/JXB/ERR225
Publisher: Wiley
Date: 12-2007
Publisher: Wiley
Date: 14-04-2015
Publisher: Springer Netherlands
Date: 2012
Publisher: Oxford University Press (OUP)
Date: 12-12-2017
DOI: 10.1093/JXB/ERX399
Publisher: Wiley
Date: 20-04-2018
DOI: 10.1111/PCE.13191
Abstract: Orthophosphate (H
Publisher: Springer Science and Business Media LLC
Date: 04-08-2015
Abstract: Proteaceae in southwestern Australia have evolved on some of the most phosphorus-impoverished soils in the world. They exhibit a range of traits that allow them to both acquire and utilize phosphorus highly efficiently. This is in stark contrast with many model plants such as Arabidopsis thaliana and crop species, which evolved on soils where nitrogen is the major limiting nutrient. When exposed to low phosphorus availability, these plants typically exhibit phosphorus-starvation responses, whereas Proteaceae do not. This Review explores the traits that account for the very high efficiency of acquisition and use of phosphorus in Proteaceae, and explores which of these traits are promising for improving the phosphorus efficiency of crop plants.
Publisher: Portland Press Ltd.
Date: 15-12-2010
DOI: 10.1042/BJ20101361
Abstract: PEPC [PEP (phosphoenolpyruvate) carboxylase] is a tightly controlled anaplerotic enzyme situated at a pivotal branch point of plant carbohydrate metabolism. Two distinct oligomeric PEPC classes were discovered in developing COS (castor oil seeds). Class-1 PEPC is a typical homotetramer of 107 kDa PTPC (plant-type PEPC) subunits, whereas the novel 910-kDa Class-2 PEPC hetero-octamer arises from a tight interaction between Class-1 PEPC and 118 kDa BTPC (bacterial-type PEPC) subunits. Mass spectrometric analysis of immunopurified COS BTPC indicated that it is subject to in vivo proline-directed phosphorylation at Ser425. We show that immunoblots probed with phosphorylation site-specific antibodies demonstrated that Ser425 phosphorylation is promoted during COS development, becoming maximal at stage IX (maturation phase) or in response to depodding. Kinetic analyses of a recombinant, chimaeric Class-2 PEPC containing phosphomimetic BTPC mutant subunits (S425D) indicated that Ser425 phosphorylation results in significant BTPC inhibition by: (i) increasing its Km(PEP) 3-fold, (ii) reducing its I50 (L-malate and L-aspartate) values by 4.5- and 2.5-fold respectively, while (iii) decreasing its activity within the physiological pH range. The developmental pattern and kinetic influence of Ser425 BTPC phosphorylation is very distinct from the in vivo phosphorylation/activation of COS Class-1 PEPC's PTPC subunits at Ser11. Collectively, the results establish that BTPC's phospho-Ser425 content depends upon COS developmental and physiological status and that Ser425 phosphorylation attenuates the catalytic activity of BTPC subunits within a Class-2 PEPC complex. To the best of our knowledge, this study provides the first evidence for protein phosphorylation as a mechanism for the in vivo control of vascular plant BTPC activity.
Publisher: Wiley
Date: 14-04-2015
Publisher: Wiley
Date: 12-06-2012
DOI: 10.1111/J.1469-8137.2012.04190.X
Abstract: Limitation of grain crop productivity by phosphorus (P) is widespread and will probably increase in the future. Enhanced P efficiency can be achieved by improved uptake of phosphate from soil (P‐acquisition efficiency) and by improved productivity per unit P taken up (P‐use efficiency). This review focuses on improved P‐use efficiency, which can be achieved by plants that have overall lower P concentrations, and by optimal distribution and redistribution of P in the plant allowing maximum growth and biomass allocation to harvestable plant parts. Significant decreases in plant P pools may be possible, for ex le, through reductions of superfluous ribosomal RNA and replacement of phospholipids by sulfolipids and galactolipids. Improvements in P distribution within the plant may be possible by increased remobilization from tissues that no longer need it (e.g. senescing leaves) and reduced partitioning of P to developing grains. Such changes would prolong and enhance the productive use of P in photosynthesis and have nutritional and environmental benefits. Research considering physiological, metabolic, molecular biological, genetic and phylogenetic aspects of P‐use efficiency is urgently needed to allow significant progress to be made in our understanding of this complex trait. Contents Summary 306 I. The need to use phosphorus efficiently 307 II. P‐use efficiency and P dynamics in a growing crop 307 III. P pools in plants 307 IV. Phosphorus pools and growth rates 310 V. Are crops different from other plants in their P concentration? 310 VI. Phosphorus use and photosynthesis 311 VII. Crop development and canopy P distribution 312 VIII. Internal redistribution of P in a growing vegetative plant 313 IX. Allocation of P to reproductive structures 314 X. Constraints to P remobilisation 315 XI. Do physiological or phylogenetic trade‐offs constrain traits that could improve PUE? 316 XII. Identifying genetic loci associated with PUE 316 XIII. Conclusions 317 Acknowledgements 317 References 317
No related grants have been discovered for William Plaxton.