1
|
Smith MA, Benidickson KH, Plaxton WC. In Vivo Phosphorylation of the Cytosolic Glucose-6-Phosphate Dehydrogenase Isozyme G6PD6 in Phosphate-Resupplied Arabidopsis thaliana Suspension Cells and Seedlings. PLANTS (BASEL, SWITZERLAND) 2023; 13:31. [PMID: 38202338 PMCID: PMC10780934 DOI: 10.3390/plants13010031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Revised: 12/11/2023] [Accepted: 12/15/2023] [Indexed: 01/12/2024]
Abstract
Glucose-6-phosphate dehydrogenase (G6PD) catalyzes the first committed step of the oxidative pentose phosphate pathway (OPPP). Our recent phosphoproteomics study revealed that the cytosolic G6PD6 isozyme became hyperphosphorylated at Ser12, Thr13 and Ser18, 48 h following phosphate (Pi) resupply to Pi-starved (-Pi) Arabidopsis thaliana cell cultures. The aim of the present study was to assess whether G6PD6 phosphorylation also occurs in shoots or roots following Pi resupply to -Pi Arabidopsis seedlings, and to investigate its relationship with G6PD activity. Interrogation of phosphoproteomic databases indicated that N-terminal, multi-site phosphorylation of G6PD6 and its orthologs is quite prevalent. However, the functions of these phosphorylation events remain unknown. Immunoblotting with an anti-(pSer18 phosphosite-specific G6PD6) antibody confirmed that G6PD6 from Pi-resupplied, but not -Pi, Arabidopsis cell cultures or seedlings (i.e., roots) was phosphorylated at Ser18; this correlated with a significant increase in extractable G6PD activity, and biomass accumulation. Peptide kinase assays of Pi-resupplied cell culture extracts indicated that G6PD6 phosphorylation at Ser18 is catalyzed by a Ca2+-dependent protein kinase (CDPK), which correlates with the 'CDPK-like' targeting motif that flanks Ser18. Our results support the hypothesis that N-terminal phosphorylation activates G6PD6 to enhance OPPP flux and thus the production of reducing power (i.e., NADPH) and C-skeletons needed to establish the rapid resumption of growth that ensures Pi-resupply to -Pi Arabidopsis.
Collapse
Affiliation(s)
| | | | - William C. Plaxton
- Department of Biology, Queen’s University, Kingston, ON K7L 3N6, Canada; (M.A.S.); (K.H.B.)
| |
Collapse
|
2
|
Kilburn R, Fedosejevs ET, Mehta D, Soleimani F, Ghahremani M, Monaghan J, Thelen JJ, Uhrig RG, Snedden WA, Plaxton WC. Substrate profiling of the Arabidopsis Ca 2+-dependent protein kinase AtCPK4 and its Ricinus communis ortholog RcCDPK1. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2023; 331:111675. [PMID: 36931565 DOI: 10.1016/j.plantsci.2023.111675] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 03/10/2023] [Accepted: 03/12/2023] [Indexed: 06/18/2023]
Abstract
AtCPK4 and AtCPK11 are Arabidopsis thaliana Ca2+-dependent protein kinase (CDPK) paralogs that have been reported to positively regulate abscisic acid (ABA) signal transduction by phosphorylating ABA-responsive transcription factor-4 (AtABF4). By contrast, RcCDPK1, their closest Ricinus communis ortholog, participates in the control of anaplerotic carbon flux in developing castor oil seeds by catalyzing inhibitory phosphorylation of bacterial-type phosphoenolpyruvate carboxylase at Ser451. LC-MS/MS revealed that AtCPK4 and RcCDPK1 transphosphorylated several common, conserved residues of AtABF4 and its castor ortholog, TRANSCRIPTION FACTOR RESPONSIBLE FOR ABA REGULATON. Arabidopsis atcpk4/atcpk11 mutants displayed an ABA-insensitive phenotype that corroborated the involvement of AtCPK4/11 in ABA signaling. A kinase-client assay was employed to identify additional AtCPK4/RcCDPK1 targets. Both CDPKs were separately incubated with a library of 2095 peptides representative of Arabidopsis protein phosphosites; five overlapping targets were identified including PLANT INTRACELLULAR RAS-GROUP-RELATED LEUCINE-RICH REPEAT PROTEIN-9 (AtPIRL9) and the E3-ubiquitin ligase ARABIDOPSIS TOXICOS EN LEVADURA 6 (AtATL6). AtPIRL9 and AtATL6 residues phosphorylated by AtCPK4/RcCDPK1 conformed to a CDPK recognition motif that was conserved amongst their respective orthologs. Collectively, this study provides evidence for novel AtCPK4/RcCDPK1 substrates, which may help to expand regulatory networks linked to Ca2+- and ABA-signaling, immune responses, and central carbon metabolism.
Collapse
Affiliation(s)
- Ryan Kilburn
- Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6
| | - Eric T Fedosejevs
- Department of Biochemistry, Christopher S. Bond Life Sciences Center, University of Missouri, 1201 Rollins Street, Columbia, MO 65211, USA
| | - Devang Mehta
- Department of Biological Sciences, University of Alberta, 11455 Saskatchewan Drive, Edmonton, Alberta, Canada T6G 2E9
| | - Faranak Soleimani
- Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6
| | - Mina Ghahremani
- Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6
| | - Jacqueline Monaghan
- Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6
| | - Jay J Thelen
- Department of Biochemistry, Christopher S. Bond Life Sciences Center, University of Missouri, 1201 Rollins Street, Columbia, MO 65211, USA
| | - R Glen Uhrig
- Department of Biological Sciences, University of Alberta, 11455 Saskatchewan Drive, Edmonton, Alberta, Canada T6G 2E9
| | - Wayne A Snedden
- Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6
| | - William C Plaxton
- Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6.
| |
Collapse
|
3
|
Kilburn R, Gerdis SA, She YM, Snedden WA, Plaxton WC. Autophosphorylation Inhibits RcCDPK1, a Dual-Specificity Kinase that Phosphorylates Bacterial-Type Phosphoenolpyruvate Carboxylase in Castor Oil Seeds. PLANT & CELL PHYSIOLOGY 2022; 63:683-698. [PMID: 35246690 DOI: 10.1093/pcp/pcac030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2022] [Revised: 03/01/2022] [Accepted: 03/04/2022] [Indexed: 06/14/2023]
Abstract
Phosphoenolpyruvate carboxylase (PEPC) is a tightly regulated enzyme that plays a crucial anaplerotic role in central plant metabolism. Bacterial-type PEPC (BTPC) of developing castor oil seeds (COS) is highly expressed as a catalytic and regulatory subunit of a novel Class-2 PEPC heteromeric complex. Ricinus communis Ca2+-dependent protein kinase-1 (RcCDPK1) catalyzes in vivo inhibitory phosphorylation of COS BTPC at Ser451. Autokinase activity of recombinant RcCDPK1 was detected and 42 autophosphorylated Ser, Thr or Tyr residues were mapped via liquid chromatography-tandem mass spectrometry. Prior autophosphorylation markedly attenuated the ability of RcCDPK1 to transphosphorylate its BTPC substrate at Ser451. However, fully dephosphorylated RcCDPK1 rapidly autophosphorylated during the initial stages of a BTPC transphosphorylation assay. This suggests that Ca2+-dependent binding of dephospho-RcCDPK1 to BTPC may trigger a structural change that leads to rapid autophosphorylation and subsequent substrate transphosphorylation. Tyr30 was identified as an autophosphorylation site via LC-MS/MS and immunoblotting with a phosphosite-specific antibody. Tyr30 occurs at the junction of RcCDPK1's N-terminal variable (NTVD) and catalytic domains and is widely conserved in plant and protist CDPKs. Interestingly, a reduced rate and extent of BTPC transphosphorylation occurred with a RcCDPK1Y30F mutant. Prior research demonstrated that RcCDPK1's NTVD is essential for its Ca2+-dependent autophosphorylation or BTPC transphosphorylation activities but plays no role in target recognition. We propose that Tyr30 autophosphorylation facilitates a Ca2+-dependent interaction between the NTVD and Ca2+-activation domain that primes RcCDPK1 for transphosphorylating BTPC at Ser451. Our results provide insights into links between the post-translational control of COS anaplerosis, Ca2+-dependent signaling and the biological significance of RcCDPK1 autophosphorylation.
Collapse
Affiliation(s)
- Ryan Kilburn
- Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada
| | - Suzanne A Gerdis
- Ottawa Research and Development Centre, Agriculture and Agri-Food Canada, Ottawa, ON K1A OC6, Canada
| | - Yi-Min She
- Centre for Biologics Evaluation, Biologic and Radiopharmaceutical Drugs Directorate, Health Canada, Ottawa, ON K1A OK9, Canada
| | - Wayne A Snedden
- Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada
| | - William C Plaxton
- Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada
| |
Collapse
|
4
|
O'Leary B, Plaxton WC. Multifaceted functions of post-translational enzyme modifications in the control of plant glycolysis. CURRENT OPINION IN PLANT BIOLOGY 2020; 55:28-37. [PMID: 32200227 DOI: 10.1016/j.pbi.2020.01.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Revised: 01/24/2020] [Accepted: 01/31/2020] [Indexed: 06/10/2023]
Abstract
Glycolysis is a central feature of metabolism and its regulation plays important roles during plant developmental and stress responses. Recent advances in proteomics and mass spectrometry have documented extensive and dynamic post-translational modifications (PTMs) of most glycolytic enzymes in diverse plant tissues. Protein PTMs represent fundamental regulatory events that integrate signalling and gene expression with cellular metabolic networks, and can regulate glycolytic enzyme activity, localization, protein:protein interactions, moonlighting functions, and turnover. Serine/threonine phosphorylation and redox PTMs of cysteine thiol groups appear to be the most prevalent forms of reversible covalent modification involved in plant glycolytic control. Additional PTMs including monoubiquitination also have important functions. However, the molecular functions and mechanisms of most glycolytic enzyme PTMs remain unknown, and represent important objectives for future studies.
Collapse
Affiliation(s)
- Brendan O'Leary
- Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley 6009, Australia
| | - William C Plaxton
- Department of Biology, Queen's University, Kingston, Ontario K7L3N6, Canada.
| |
Collapse
|
5
|
Ghahremani M, Tran H, Biglou SG, O'Gallagher B, She YM, Plaxton WC. A glycoform of the secreted purple acid phosphatase AtPAP26 co-purifies with a mannose-binding lectin (AtGAL1) upregulated by phosphate-starved Arabidopsis. PLANT, CELL & ENVIRONMENT 2019; 42:1139-1157. [PMID: 30156702 DOI: 10.1111/pce.13432] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Revised: 08/21/2018] [Accepted: 08/22/2018] [Indexed: 05/08/2023]
Abstract
The purple acid phosphatase AtPAP26 plays a central role in Pi-scavenging by Pi-starved (-Pi) Arabidopsis. Mass spectrometry (MS) of AtPAP26-S1 and AtPAP26-S2 glycoforms secreted by -Pi suspension cells demonstrated that N-glycans at Asn365 and Asn422 were modified in AtPAP26-S2 to form high-mannose glycans. A 55-kDa protein that co-purified with AtPAP26-S2 was identified as a Galanthus nivalis agglutinin-related and apple domain lectin-1 (AtGAL1; At1g78850). MS revealed that AtGAL1 was bisphosphorylated at Tyr38 and Thr39 and glycosylated at four conserved Asn residues. When AtGAL was incubated in the presence of a thiol-reducing reagent prior to immunoblotting, its cross-reactivity with anti-AtGAL1-IgG was markedly attenuated (consistent with three predicted disulfide bonds in AtGAL1's apple domain). Secreted AtGAL1 polypeptides were upregulated to a far greater extent than AtGAL1 transcripts during Pi deprivation, indicating posttranscriptional control of AtGAL1 expression. Growth of a -Pi atgal1 mutant was unaffected, possibly due to compensation by AtGAL1's closest paralog, AtGAL2 (At1g78860). Nevertheless, AtGAL1's induction by numerous stresses combined with the broad distribution of AtGAL1-like lectins in diverse species implies an important function for AtGAL1 orthologs within the plant kingdom. We hypothesize that binding of AtPAP26-S2's high-mannose glycans by AtGAL1 enhances AtPAP26 function to facilitate Pi-scavenging by -Pi Arabidopsis.
Collapse
Affiliation(s)
| | - Hue Tran
- Oncolytics Biotech Inc., Calgary, Canada
| | - Sanaz G Biglou
- Department of Biology, Queen's University, Kingston, Canada
| | | | - Yi-Min She
- Centre for Biologics Evaluation, Biologics and Genetic Therapies Directorate, Health Canada, Ottawa, Canada
| | - William C Plaxton
- Department of Biology, Queen's University, Kingston, Canada
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Canada
| |
Collapse
|
6
|
Enhanced biomass production by Phaeodactylum tricornutum overexpressing phosphoenolpyruvate carboxylase. ALGAL RES 2018. [DOI: 10.1016/j.algal.2017.08.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
|
7
|
Ting MKY, She YM, Plaxton WC. Transcript profiling indicates a widespread role for bacterial-type phosphoenolpyruvate carboxylase in malate-accumulating sink tissues. JOURNAL OF EXPERIMENTAL BOTANY 2017; 68:5857-5869. [PMID: 29240945 PMCID: PMC5854131 DOI: 10.1093/jxb/erx399] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Phosphoenolpyruvate carboxylase (PEPC) is an important regulatory enzyme situated at a key branch point of central plant metabolism. Plant genomes encode several plant-type PEPC (PTPC) isozymes, along with a distantly related bacterial-type PEPC (BTPC). BTPC is expressed at high levels in developing castor oil seeds where it tightly interacts with co-expressed PTPC polypeptides to form unusual hetero-octameric Class-2 PEPC complexes that are desensitized to allosteric inhibition by L-malate. Analysis of RNA-Seq and microarray transcriptome datasets revealed two distinct patterns of tissue-specific BTPC expression in vascular plants. Species such as Arabidopsis thaliana, strawberry, rice, maize, and poplar mainly exhibited pollen- or floral-specific BTPC expression. By contrast, BTPC transcripts were relatively abundant in developing castor, cotton, and soybean seeds, cassava tubers, as well as immature tomato, cucumber, grape, and avocado fruit. Immunoreactive 118 kDa BTPC polypeptides were detected on immunoblots of cucumber and tomato fruit extracts. Co-immunoprecipitation established that as in castor, BTPCs physically interact with endogenous PTPCs to form Class-2 PEPC complexes in tomato and cucumber fruit. We hypothesize that Class-2 PEPCs simultaneously maintain rapid anaplerotic PEP carboxylation and respiratory CO2 refixation in diverse, biosynthetically active sinks that accumulate high malate levels.
Collapse
Affiliation(s)
- Michael K Y Ting
- Department of Biology, Queen’s University, Kingston, Ontario, Canada
| | - Yi-Min She
- Centre for Biologics Evaluation Biologics and Genetic Therapies Directorate, Health Canada, Ottawa, Ontario, Canada
| | - William C Plaxton
- Department of Biology, Queen’s University, Kingston, Ontario, Canada
- Department of Biomedical and Molecular Sciences, Queen’s University, Kingston, Ontario, Canada
- Correspondence:
| |
Collapse
|
8
|
Covarrubias AA, Cuevas-Velazquez CL, Romero-Pérez PS, Rendón-Luna DF, Chater CCC. Structural disorder in plant proteins: where plasticity meets sessility. Cell Mol Life Sci 2017; 74:3119-3147. [PMID: 28643166 PMCID: PMC11107788 DOI: 10.1007/s00018-017-2557-2] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 06/01/2017] [Indexed: 01/08/2023]
Abstract
Plants are sessile organisms. This intriguing nature provokes the question of how they survive despite the continual perturbations caused by their constantly changing environment. The large amount of knowledge accumulated to date demonstrates the fascinating dynamic and plastic mechanisms, which underpin the diverse strategies selected in plants in response to the fluctuating environment. This phenotypic plasticity requires an efficient integration of external cues to their growth and developmental programs that can only be achieved through the dynamic and interactive coordination of various signaling networks. Given the versatility of intrinsic structural disorder within proteins, this feature appears as one of the leading characters of such complex functional circuits, critical for plant adaptation and survival in their wild habitats. In this review, we present information of those intrinsically disordered proteins (IDPs) from plants for which their high level of predicted structural disorder has been correlated with a particular function, or where there is experimental evidence linking this structural feature with its protein function. Using examples of plant IDPs involved in the control of cell cycle, metabolism, hormonal signaling and regulation of gene expression, development and responses to stress, we demonstrate the critical importance of IDPs throughout the life of the plant.
Collapse
Affiliation(s)
- Alejandra A Covarrubias
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, 62250, Cuernavaca, Mexico.
| | - Cesar L Cuevas-Velazquez
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, 62250, Cuernavaca, Mexico
| | - Paulette S Romero-Pérez
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, 62250, Cuernavaca, Mexico
| | - David F Rendón-Luna
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, 62250, Cuernavaca, Mexico
| | - Caspar C C Chater
- Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, 62250, Cuernavaca, Mexico
| |
Collapse
|
9
|
O’Leary BM, Plaxton WC. Mechanisms and Functions of Post-translational Enzyme Modifications in the Organization and Control of Plant Respiratory Metabolism. ADVANCES IN PHOTOSYNTHESIS AND RESPIRATION 2017. [DOI: 10.1007/978-3-319-68703-2_13] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
|
10
|
The calcium-dependent protein kinase RcCDPK2 phosphorylates sucrose synthase at Ser11 in developing castor oil seeds. Biochem J 2016; 473:3667-3682. [PMID: 27512054 DOI: 10.1042/bcj20160531] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Accepted: 08/10/2016] [Indexed: 12/11/2022]
Abstract
Imported sucrose is cleaved by sucrose synthase (SUS) as a critical initial reaction in the biosynthesis of storage end-products by developing seeds. Although SUS is phosphorylated at a conserved seryl residue by an apparent CDPK (Ca2+-dependent protein kinase) in diverse plant tissues, the functions and mechanistic details of this process remain obscure. Thus, the native CDPK that phosphorylates RcSUS1 (Ricinus communis SUS1) at Ser11 in developing COS (castor oil seeds) was highly purified and identified as RcCDPK2 by MS/MS. Purified RcSUS1-K (-kinase) and heterologously expressed RcCDPK2 catalyzed Ca2+-dependent Ser11 phosphorylation of RcSUS1 and its corresponding dephosphopeptide, while exhibiting a high affinity for free Ca2+ ions [K0.5(Ca2+) < 0.4 µM]. RcSUS1-K activity, RcCDPK2 expression, and RcSUS1 Ser11 phosphorylation peaked during early COS development and then declined in parallel. The elimination of sucrose import via fruit excision triggered RcSUS1 dephosphorylation but did not alter RcSUS1-K activity, suggesting a link between sucrose signaling and posttranslational RcCDPK2 control. Both RcCDPK2-mCherry and RcSUS1-EYFP co-localized throughout the cytosol when transiently co-expressed in tobacco suspension cells, although RcCDPK2-mCherry was also partially localized to the nucleus. Subcellular fractionation revealed that ∼20% of RcSUS1-K activity associates with microsomal membranes in developing COS, as does RcSUS1. In contrast with RcCDPK1, which catalyzes inhibitory phosphorylation of COS bacterial-type phosphoenolpyruvate carboxylase at Ser451, RcCDPK2 exhibited broad substrate specificity, a wide pH-activity profile centered at pH 8.5, and insensitivity to metabolite effectors or thiol redox status. Our combined results indicate a possible link between cytosolic Ca2+-signaling and the control of photosynthate partitioning during COS development.
Collapse
|
11
|
Fedosejevs ET, Ying S, Park J, Anderson EM, Mullen RT, She YM, Plaxton WC. Biochemical and molecular characterization of RcSUS1, a cytosolic sucrose synthase phosphorylated in vivo at serine 11 in developing castor oil seeds. J Biol Chem 2014; 289:33412-24. [PMID: 25313400 PMCID: PMC4246097 DOI: 10.1074/jbc.m114.585554] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Revised: 10/06/2014] [Indexed: 11/06/2022] Open
Abstract
Sucrose synthase (SUS) catalyzes the UDP-dependent cleavage of sucrose into UDP-glucose and fructose and has become an important target for improving seed crops via metabolic engineering. A UDP-specific SUS homotetramer composed of 93-kDa subunits was purified to homogeneity from the triacylglyceride-rich endosperm of developing castor oil seeds (COS) and identified as RcSUS1 by mass spectrometry. RcSUS1 transcripts peaked during early development, whereas levels of SUS activity and immunoreactive 93-kDa SUS polypeptides maximized during mid-development, becoming undetectable in fully mature COS. The cytosolic location of the enzyme was established following transient expression of RcSUS1-enhanced YFP in tobacco suspension cells and fluorescence microscopy. Immunological studies using anti-phosphosite-specific antibodies revealed dynamic and high stoichiometric in vivo phosphorylation of RcSUS1 at its conserved Ser-11 residue during COS development. Incorporation of (32)P(i) from [γ-(32)P]ATP into a RcSUS1 peptide substrate, alongside a phosphosite-specific ELISA assay, established the presence of calcium-dependent RcSUS1 (Ser-11) kinase activity. Approximately 10% of RcSUS1 was associated with COS microsomal membranes and was hypophosphorylated relative to the remainder of RcSUS1 that partitioned into the soluble, cytosolic fraction. Elimination of sucrose supply caused by excision of intact pods of developing COS abolished RcSUS1 transcription while triggering the progressive dephosphorylation of RcSUS1 in planta. This did not influence the proportion of RcSUS1 associated with microsomal membranes but instead correlated with a subsequent marked decline in SUS activity and immunoreactive RcSUS1 polypeptides. Phosphorylation at Ser-11 appears to protect RcSUS1 from proteolysis, rather than influence its kinetic properties or partitioning between the soluble cytosol and microsomal membranes.
Collapse
Affiliation(s)
| | | | - Joonho Park
- the Department of Fine Chemistry, Seoul National University of Science and Technology, Nowon-Gu, Seoul 139-743, Korea
| | - Erin M Anderson
- the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada, and
| | - Robert T Mullen
- the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada, and
| | - Yi-Min She
- the Shanghai Center for Plant Stress Biology, Chinese Academy of Sciences, Shanghai 201602, China
| | - William C Plaxton
- From the Departments of Biology and Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario K7L 3N6, Canada,
| |
Collapse
|
12
|
Phosphorylation of bacterial-type phosphoenolpyruvate carboxylase by a Ca2+-dependent protein kinase suggests a link between Ca2+ signalling and anaplerotic pathway control in developing castor oil seeds. Biochem J 2014; 458:109-18. [PMID: 24266766 DOI: 10.1042/bj20131191] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The aim of the present study was to characterize the native protein kinase [BTPC (bacterial-type phosphoenolpyruvate carboxylase)-K (BTPC Ser451 kinase)] that in vivo phosphorylates Ser451 of the BTPC subunits of an unusual Class-2 PEP (phosphoenolpyruvate) carboxylase hetero-octameric complex of developing COS (castor oil seeds). COS BTPC-K was highly purified by PEG fractionation and hydrophobic size-exclusion anion-exchange and affinity chromatographies. BTPC-K phosphorylated BTPC strictly at Ser451 (Km=1.0 μM; pH optimum=7.3), a conserved target residue occurring within an intrinsically disordered region, as well as the protein histone III-S (Km=1.7 μM), but not a COS plant-type PEP carboxylase or sucrose synthase or α-casein. Its activity was Ca2+- (K0.5=2.7 μM) and ATP- (Km=6.6 μM) dependent, and markedly inhibited by trifluoperazine, 3-phosphoglycerate and PEP, but insensitive to calmodulin or 14-3-3 proteins. BTPC-K exhibited a native molecular mass of ~63 kDa and was soluble rather than membrane-bound. Inactivation and reactivation occurred upon BTPC-K's incubation with GSSG and then DTT respectively. Ser451 phosphorylation by BTPC-K inhibited BTPC activity by ~50% when assayed under suboptimal conditions (pH 7.3, 1 mM PEP and 10 mM L-malate). Our collective results indicate a possible link between cytosolic Ca2+ signalling and anaplerotic flux control in developing COS.
Collapse
|
13
|
Park J, Khuu N, Howard ASM, Mullen RT, Plaxton WC. Bacterial- and plant-type phosphoenolpyruvate carboxylase isozymes from developing castor oil seeds interact in vivo and associate with the surface of mitochondria. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2012; 71:251-62. [PMID: 22404138 DOI: 10.1111/j.1365-313x.2012.04985.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Phosphoenolpyruvate carboxylase (PEPC) from developing castor oil seeds (COS) exists as two distinct oligomeric isoforms. The typical class-1 PEPC homotetramer consists of 107-kDa plant-type PEPC (PTPC) subunits, whereas the allosterically desensitized 910-kDa class-2 PEPC hetero-octamer arises from the association of class-1 PEPC with 118-kDa bacterial-type PEPC (BTPC) subunits. The in vivo interaction and subcellular location of COS BTPC and PTPC were assessed by imaging fluorescent protein (FP)-tagged PEPCs in tobacco suspension-cultured cells. The BTPC-FP mainly localized to cytoplasmic punctate/globular structures, identified as mitochondria by co-immunostaining of endogenous cytochrome oxidase. Inhibition of respiration with KCN resulted in proportional decreases and increases in mitochondrial versus cytosolic BTPC-FP, respectively. The FP-PTPC and NLS-FP-PTPC (containing an appended nuclear localization signal, NLS) localized to the cytosol and nucleus, respectively, but both co-localized with mitochondrial-associated BTPC when co-expressed with BTPC-FP. Transmission electron microscopy of immunogold-labeled developing COS revealed that BTPC and PTPC are localized at the mitochondrial (outer) envelope, as well as the cytosol. Moreover, thermolysin-sensitive BTPC and PTPC polypeptides were detected on immunoblots of purified COS mitochondria. Overall, our results demonstrate that: (i) COS BTPC and PTPC interact in vivo as a class-2 PEPC complex that associates with the surface of mitochondria, (ii) BTPC's unique and divergent intrinsically disordered region mediates its interaction with PTPC, whereas (iii) the PTPC-containing class-1 PEPC is entirely cytosolic. We hypothesize that mitochondrial-associated class-2 PEPC facilitates rapid refixation of respiratory CO(2) while sustaining a large anaplerotic flux to replenish tricarboxylic acid cycle C-skeletons withdrawn for biosynthesis.
Collapse
Affiliation(s)
- Joonho Park
- Department of Biology, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | | | | | | | | |
Collapse
|