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Mao W, Lazar N, van Tilbeurgh H, Loiseau PM, Pomel S. Minor Impact of A258D Mutation on Biochemical and Enzymatic Properties of Leishmania infantum GDP-Mannose Pyrophosphorylase. Microorganisms 2022; 10:microorganisms10020231. [PMID: 35208687 PMCID: PMC8877407 DOI: 10.3390/microorganisms10020231] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Accepted: 01/17/2022] [Indexed: 02/01/2023] Open
Abstract
Background: Leishmaniasis, a vector-borne disease caused by the protozoan parasite from the genus Leishmania, is endemic to tropical and subtropical areas. Few treatments are available against leishmaniasis, with all presenting issues of toxicity, resistance, and/or cost. In this context, the development of new antileishmanial drugs is urgently needed. GDP-mannose pyrophosphorylase (GDP-MP), an enzyme involved in the mannosylation pathway, has been described to constitute an attractive therapeutic target for the development of specific antileishmanial agents. Methods: In this work, we produced, purified, and analyzed the enzymatic properties of the recombinant L. infantum GDP-MP (LiGDP-MP), a single leishmanial GDP-MP that presents mutation of an aspartate instead of an alanine at position 258, which is also the single residue difference with the homolog in L. donovani: LdGDP-MP. Results: The purified LiGDP-MP displayed high substrate and cofactor specificities, a sequential random mechanism of reaction, and the following kinetic constants: Vm at 0.6 µM·min−1, Km from 15–18 µM, kcat from 12.5–13 min−1, and kcat/Km at around 0.8 min−1µM−1. Conclusions: These results show that LiGDP-MP has similar biochemical and enzymatic properties to LdGDP-MP. Further studies are needed to determine the advantage for L. infantum of the A258D residue change in GDP-MP.
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Affiliation(s)
- Wei Mao
- Université Paris-Saclay, CNRS, BioCIS, 92290 Châtenay-Malabry, France; (W.M.); (P.M.L.)
| | - Noureddine Lazar
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France; (N.L.); (H.v.T.)
| | - Herman van Tilbeurgh
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France; (N.L.); (H.v.T.)
| | - Philippe M. Loiseau
- Université Paris-Saclay, CNRS, BioCIS, 92290 Châtenay-Malabry, France; (W.M.); (P.M.L.)
| | - Sébastien Pomel
- Université Paris-Saclay, CNRS, BioCIS, 92290 Châtenay-Malabry, France; (W.M.); (P.M.L.)
- Correspondence:
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Zangelmi E, Ronda L, Castagna C, Campanini B, Veiga-da-Cunha M, Van Schaftingen E, Peracchi A. Off to a slow start: Analyzing lag phases and accelerating rates in steady-state enzyme kinetics. Anal Biochem 2020; 593:113595. [PMID: 31987861 DOI: 10.1016/j.ab.2020.113595] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Revised: 01/10/2020] [Accepted: 01/20/2020] [Indexed: 10/25/2022]
Abstract
Steady-state enzyme kinetics typically relies on the measurement of 'initial rates', obtained when the substrate is not significantly consumed and the amount of product formed is negligible. Although initial rates are usually faster than those measured later in the reaction time-course, sometimes the speed of the reaction appears instead to increase with time, reaching a steady level only after an initial delay or 'lag phase'. This behavior needs to be interpreted by the experimentalists. To assist interpretation, this article analyzes the many reasons why, during an enzyme assay, the observed rate can be slow in the beginning and then progressively accelerate. The possible causes range from trivial artifacts to instances in which deeper mechanistic or biophysical factors are at play. We provide practical examples for most of these causes, based firstly on experiments conducted with ornithine δ-aminotransferase and with other pyridoxal-phosphate dependent enzymes that have been studied in our laboratory. On the side to this survey, we provide evidence that the product of the ornithine δ-aminotransferase reaction, glutamate 5-semialdehyde, cyclizes spontaneously to pyrroline 5-carboxylate with a rate constant greater than 3 s-1.
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Affiliation(s)
- Erika Zangelmi
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124, Parma, Italy
| | - Luca Ronda
- Department of Medicine and Surgery, University of Parma, 43126, Parma, Italy
| | - Camilla Castagna
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124, Parma, Italy
| | - Barbara Campanini
- Department of Food and Drug, University of Parma, 43124, Parma, Italy
| | - Maria Veiga-da-Cunha
- De Duve Institute and WELBIO, UCLouvain, Avenue Hippocrate 75, 1200, Bruxelles, Belgium
| | - Emile Van Schaftingen
- De Duve Institute and WELBIO, UCLouvain, Avenue Hippocrate 75, 1200, Bruxelles, Belgium
| | - Alessio Peracchi
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, 43124, Parma, Italy.
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Pomel S, Mao W, Ha-Duong T, Cavé C, Loiseau PM. GDP-Mannose Pyrophosphorylase: A Biologically Validated Target for Drug Development Against Leishmaniasis. Front Cell Infect Microbiol 2019; 9:186. [PMID: 31214516 PMCID: PMC6554559 DOI: 10.3389/fcimb.2019.00186] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Accepted: 05/15/2019] [Indexed: 01/02/2023] Open
Abstract
Leishmaniases are neglected tropical diseases that threaten about 350 million people in 98 countries around the world. In order to find new antileishmanial drugs, an original approach consists in reducing the pathogenic effect of the parasite by impairing the glycoconjugate biosynthesis, necessary for parasite recognition and internalization by the macrophage. Some proteins appear to be critical in this way, and one of them, the GDP-Mannose Pyrophosphorylase (GDP-MP), is an attractive target for the design of specific inhibitors as it is essential for Leishmania survival and it presents significant differences with the host counterpart. Two GDP-MP inhibitors, compounds A and B, have been identified in two distinct studies by high throughput screening and by a rational approach based on molecular modeling, respectively. Compound B was found to be the most promising as it exhibited specific competitive inhibition of leishmanial GDP-MP and antileishmanial activities at the micromolar range with interesting selectivity indexes, as opposed to compound A. Therefore, compound B can be used as a pharmacological tool for the development of new specific antileishmanial drugs.
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Affiliation(s)
- Sébastien Pomel
- UMR 8076 CNRS BioCIS, Université Paris-Sud, Université Paris-Saclay, Châtenay-Malabry, France
| | - Wei Mao
- UMR 8076 CNRS BioCIS, Université Paris-Sud, Université Paris-Saclay, Châtenay-Malabry, France
| | - Tâp Ha-Duong
- UMR 8076 CNRS BioCIS, Université Paris-Sud, Université Paris-Saclay, Châtenay-Malabry, France
| | - Christian Cavé
- UMR 8076 CNRS BioCIS, Université Paris-Sud, Université Paris-Saclay, Châtenay-Malabry, France
| | - Philippe M Loiseau
- UMR 8076 CNRS BioCIS, Université Paris-Sud, Université Paris-Saclay, Châtenay-Malabry, France
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Abstract
Starch is a plant storage polyglucan that accumulates in plastids. It is composed of two polymers, amylose and amylopectin, with different structures and plays several roles in helping to determine plant yield. In leaves, it acts as a buffer for night time carbon starvation. Genetically altered plants that cannot synthesize or degrade starch efficiently often grow poorly. There have been a number of successful approaches to manipulate leaf starch metabolism that has resulted in increased growth and yield. Its degradation is also a source of sugars that can help alleviate abiotic stress. In edible parts of plants, starch often makes up the majority of the dry weight constituting much of the calorific value of food and feed. Increasing starch in these organs can increase this as well as increasing yield. Enzymes involved in starch metabolism are well known, and there has been much research analyzing their functions in starch synthesis and degradation, as well as genetic and posttranslational regulatory mechanisms affecting them. In this mini review, we examine work on this topic and discuss future directions that could be used to manipulate this metabolite for improved yield.
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Affiliation(s)
| | - Jens Kossmann
- Department of Genetics, Institute for Plant Biotechnology, University of Stellenbosch, Stellenbosch, South Africa
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Figueroa CM, Kuhn ML, Hill BL, Iglesias AA, Ballicora MA. Resurrecting the Regulatory Properties of the Ostreococcus tauri ADP-Glucose Pyrophosphorylase Large Subunit. Front Plant Sci 2018; 9:1564. [PMID: 30425723 PMCID: PMC6218581 DOI: 10.3389/fpls.2018.01564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Accepted: 10/05/2018] [Indexed: 05/09/2023]
Abstract
ADP-glucose pyrophosphorylase (ADP-Glc PPase) catalyzes the first committed step for the synthesis of glycogen in cyanobacteria and starch in green algae and plants. The enzyme from cyanobacteria is homotetrameric (α4), while that from green algae and plants is heterotetrameric (α2β2). These ADP-Glc PPases are allosterically regulated by 3-phosphoglycerate (3PGA, activator) and inorganic orthophosphate (Pi, inhibitor). Previous studies on the cyanobacterial and plant enzymes showed that 3PGA binds to two highly conserved Lys residues located in the C-terminal domain. We observed that both Lys residues are present in the small (α) subunit of the Ostreococcus tauri enzyme; however, one of these Lys residues is replaced by Arg in the large (β) subunit. In this work, we obtained the K443R and R466K mutants of the O. tauri small and large subunits, respectively, and co-expressed them together or with their corresponding wild type counterparts. Our results show that restoring the Lys residue in the large subunit enhanced 3PGA affinity, whereas introduction of an Arg residue in the small subunit reduced 3PGA affinity of the heterotetramers. Inhibition kinetics also showed that heterotetramers containing the K443R small subunit mutant were less sensitive to Pi inhibition, but only minor changes were observed for those containing the R466K large subunit mutant, suggesting a leading role of the small subunit for Pi inhibition of the heterotetramer. We conclude that, during evolution, the ADP-Glc PPase large subunit from green algae and plants acquired mutations in its regulatory site. The rationale for this could have been to accommodate sensitivity to particular metabolic needs of the cell or tissue.
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Affiliation(s)
- Carlos M. Figueroa
- Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, IL, United States
- Instituto de Agrobiotecnología del Litoral, Universidad Nacional del Litoral, CONICET, Facultad de Bioquímica y Ciencias Biológicas, Santa Fe, Argentina
| | - Misty L. Kuhn
- Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, IL, United States
| | - Benjamin L. Hill
- Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, IL, United States
| | - Alberto A. Iglesias
- Instituto de Agrobiotecnología del Litoral, Universidad Nacional del Litoral, CONICET, Facultad de Bioquímica y Ciencias Biológicas, Santa Fe, Argentina
- *Correspondence: Alberto A. Iglesias, Miguel A. Ballicora,
| | - Miguel A. Ballicora
- Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, IL, United States
- *Correspondence: Alberto A. Iglesias, Miguel A. Ballicora,
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Hannah LC, Shaw JR, Clancy MA, Georgelis N, Boehlein SK. A brittle-2 transgene increases maize yield by acting in maternal tissues to increase seed number. Plant Direct 2017; 1:e00029. [PMID: 31245677 PMCID: PMC6508519 DOI: 10.1002/pld3.29] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 11/03/2017] [Accepted: 11/14/2017] [Indexed: 05/24/2023]
Abstract
The enzyme ADP-glucose pyrophosphorylase is essential for starch biosynthesis and is highly regulated. Here, mutations that increased heat stability and interactions with allosteric effectors were incorporated into the small subunit of the isoform known to be expressed at high levels in the maize endosperm. The resulting variants were transformed into maize with expression targeted to the endosperm. Transgenes harboring the changes increased yield some 35%; however, yield enhancement occurred via an increase in seed number rather than by increased seed weight. Interestingly, seed number increase is controlled by the genotype of the plant rather than the genotype of the seed as seeds increase in number whether or not they contain the transgene as long as the maternal parent has the transgene. The transgene is however expressed in the endosperm, and the altered allosteric and stability properties initially seen in Escherichia coli expression experiments are also seen with the endosperm-expressed gene. The extent of seed number increase is positively correlated with the average daily high temperature during the first 4 days postpollination. While these results were unexpected, they echo the phenotypic changes caused by the insertion of an altered large subunit of this enzyme reported previously (Plant Cell, 24, 2012, 2352). These results call into question some of the reported fundamental differences separating starch synthesis in the endosperm vis-à-vis other plant tissues.
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Affiliation(s)
- L. Curtis Hannah
- Program in Plant Molecular and Cellular BiologyDepartment of Horticultural SciencesUniversity of FloridaGainesvilleFLUSA
| | - Janine R. Shaw
- Program in Plant Molecular and Cellular BiologyDepartment of Horticultural SciencesUniversity of FloridaGainesvilleFLUSA
| | - Maureen A. Clancy
- Program in Plant Molecular and Cellular BiologyDepartment of Horticultural SciencesUniversity of FloridaGainesvilleFLUSA
| | - Nikolaos Georgelis
- Program in Plant Molecular and Cellular BiologyDepartment of Horticultural SciencesUniversity of FloridaGainesvilleFLUSA
- Present address:
Simplot Plant SciencesJ.R. Simplot CompanyBoiseIDUSA
| | - Susan K. Boehlein
- Program in Plant Molecular and Cellular BiologyDepartment of Horticultural SciencesUniversity of FloridaGainesvilleFLUSA
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7
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Mao W, Daligaux P, Lazar N, Ha-Duong T, Cavé C, van Tilbeurgh H, Loiseau PM, Pomel S. Biochemical analysis of leishmanial and human GDP-Mannose Pyrophosphorylases and selection of inhibitors as new leads. Sci Rep 2017; 7:751. [PMID: 28389670 DOI: 10.1038/s41598-017-00848-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 03/16/2017] [Indexed: 12/12/2022] Open
Abstract
Leishmaniases are an ensemble of diseases caused by the protozoan parasite of the genus Leishmania. Current antileishmanial treatments are limited and present main issues of toxicity and drug resistance emergence. Therefore, the generation of new inhibitors specifically directed against a leishmanial target is an attractive strategy to expand the chemotherapeutic arsenal. GDP-Mannose Pyrophosphorylase (GDP-MP) is a prominent therapeutic target involved in host-parasite recognition which has been described to be essential for parasite survival. In this work, we produced and purified GDP-MPs from L. mexicana (LmGDP-MP), L. donovani (LdGDP-MP), and human (hGDP-MP), and compared their enzymatic properties. From a rationale design of 100 potential inhibitors, four compounds were identified having a promising and specific inhibitory effect on parasite GDP-MP and antileishmanial activities, one of them exhibits a competitive inhibition on LdGDP-MP and belongs to the 2-substituted quinoline series.
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8
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Cakir B, Tuncel A, Green AR, Koper K, Hwang SK, Okita TW, Kang C. Substrate binding properties of potato tuber ADP-glucose pyrophosphorylase as determined by isothermal titration calorimetry. FEBS Lett 2015; 589:1444-9. [PMID: 25953126 DOI: 10.1016/j.febslet.2015.04.042] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Revised: 04/14/2015] [Accepted: 04/21/2015] [Indexed: 11/15/2022]
Abstract
Substrate binding properties of the large (LS) and small (SS) subunits of potato tuber ADP-glucose pyrophosphorylase were investigated by using isothermal titration calorimetry. Our results clearly show that the wild type heterotetramer (S(WT)L(WT)) possesses two distinct types of ATP binding sites, whereas the homotetrameric LS and SS variant forms only exhibited properties of one of the two binding sites. The wild type enzyme also exhibited significantly increased affinity to this substrate compared to the homotetrameric enzyme forms. No stable binding was evident for the second substrate, glucose-1-phosphate, in the presence or absence of ATPγS suggesting that interaction of glucose-1-phosphate is dependent on hydrolysis of ATP and supports the Theorell-Chance bi bi reaction mechanism.
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Affiliation(s)
- Bilal Cakir
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA
| | - Aytug Tuncel
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA
| | - Abigail R Green
- School of Molecular Biosciences, Washington State University, Pullman, WA 99164, USA
| | - Kaan Koper
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA
| | - Seon-Kap Hwang
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA
| | - Thomas W Okita
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA.
| | - ChulHee Kang
- School of Molecular Biosciences, Washington State University, Pullman, WA 99164, USA.
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Boehlein SK, Shaw JR, Stewart JD, Sullivan B, Hannah LC. Enhancing the heat stability and kinetic parameters of the maize endosperm ADP-glucose pyrophosphorylase using iterative saturation mutagenesis. Arch Biochem Biophys 2015; 568:28-37. [DOI: 10.1016/j.abb.2015.01.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Revised: 01/08/2015] [Accepted: 01/11/2015] [Indexed: 11/30/2022]
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Tuncel A, Kawaguchi J, Ihara Y, Matsusaka H, Nishi A, Nakamura T, Kuhara S, Hirakawa H, Nakamura Y, Cakir B, Nagamine A, Okita TW, Hwang SK, Satoh H. The rice endosperm ADP-glucose pyrophosphorylase large subunit is essential for optimal catalysis and allosteric regulation of the heterotetrameric enzyme. Plant Cell Physiol 2014; 55:1169-83. [PMID: 24747952 DOI: 10.1093/pcp/pcu057] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Although an alternative pathway has been suggested, the prevailing view is that starch synthesis in cereal endosperm is controlled by the activity of the cytosolic isoform of ADPglucose pyrophosphorylase (AGPase). In rice, the cytosolic AGPase isoform is encoded by the OsAGPS2b and OsAGPL2 genes, which code for the small (S2b) and large (L2) subunits of the heterotetrameric enzyme, respectively. In this study, we isolated several allelic missense and nonsense OsAGPL2 mutants by N-methyl-N-nitrosourea (MNU) treatment of fertilized egg cells and by TILLING (Targeting Induced Local Lesions in Genomes). Interestingly, seeds from three of the missense mutants (two containing T139I and A171V) were severely shriveled and had seed weight and starch content comparable with the shriveled seeds from OsAGPL2 null mutants. Results from kinetic analysis of the purified recombinant enzymes revealed that the catalytic and allosteric regulatory properties of these mutant enzymes were significantly impaired. The missense heterotetramer enzymes and the S2b homotetramer had lower specific (catalytic) activities and affinities for the activator 3-phosphoglycerate (3-PGA). The missense heterotetramer enzymes showed more sensitivity to inhibition by the inhibitor inorganic phosphate (Pi) than the wild-type AGPase, while the S2b homotetramer was profoundly tolerant to Pi inhibition. Thus, our results provide definitive evidence that starch biosynthesis during rice endosperm development is controlled predominantly by the catalytic activity of the cytoplasmic AGPase and its allosteric regulation by the effectors. Moreover, our results show that the L2 subunit is essential for both catalysis and allosteric regulatory properties of the heterotetramer enzyme.
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Affiliation(s)
- Aytug Tuncel
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USAThese authors contributed equally to this work
| | - Joe Kawaguchi
- Faculty of Agriculture, Kyushu University, Fukuoka, 812-8581 JapanThese authors contributed equally to this work
| | - Yasuharu Ihara
- Faculty of Agriculture, Kyushu University, Fukuoka, 812-8581 Japan
| | | | - Aiko Nishi
- Faculty of Agriculture, Kyushu University, Fukuoka, 812-8581 Japan
| | | | - Satoru Kuhara
- Department of Genetic Resources Technology, Kyushu University, Fukuoka, 812-8581 Japan
| | - Hideki Hirakawa
- Kazusa DNA Research Institute, Department of Plant Genome Research, Kisarazu, Japan
| | - Yasunori Nakamura
- Faculty of Bioresource Sciences, Akita Prefectural University, Akita City, 010-0195 Japan
| | - Bilal Cakir
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA
| | - Ai Nagamine
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USAFaculty of Agriculture, Kyushu University, Fukuoka, 812-8581 Japan
| | - Thomas W Okita
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA
| | - Seon-Kap Hwang
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99164, USA
| | - Hikaru Satoh
- Faculty of Agriculture, Kyushu University, Fukuoka, 812-8581 Japan
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Boehlein SK, Shaw JR, Georgelis N, Hannah LC. Enhanced heat stability and kinetic parameters of maize endosperm ADPglucose pyrophosphorylase by alteration of phylogenetically identified amino acids. Arch Biochem Biophys 2013; 543:1-9. [PMID: 24378757 DOI: 10.1016/j.abb.2013.12.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2013] [Revised: 12/12/2013] [Accepted: 12/20/2013] [Indexed: 10/25/2022]
Abstract
ADP-glucose pyrophosphorylase (AGPase) controls the rate-limiting step in starch biosynthesis and is regulated at various levels. Cereal endosperm enzymes, in contrast to other plant AGPases, are particularly heat labile and transgenic studies highlight the importance of temperature for cereal yield. Previously, a phylogenetic approach identified Type II and positively selected amino acid positions in the large subunit of maize endosperm AGPase. Glycogen content, kinetic parameters and heat stability were measured in AGPases having mutations in these sites and interesting differences were observed. This study expands on our earlier evolutionary work by determining how all Type II and positively selected sites affect kinetic constants, heat stability and catalytic rates at increased temperatures. Variants with enhanced properties were identified and combined into one gene, designated Sh2-E. Enhanced properties include: heat stability, enhanced activity at 37 °C, activity at 55 °C, reduced Ka and activity in the absence of activator. The resulting enzyme exhibited all improved properties of the various individual changes. Additionally, Sh2-E was expressed with a small subunit variant with enhanced enzyme properties resulting in an enzyme that has exceptional heat stability, a high catalytic rate at increased temperatures and significantly decreased Km values for both substrates in the absence of the activator.
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Affiliation(s)
- Susan K Boehlein
- 1253 Fifield Hall, University of Florida, Gainesville, FL 32611, USA
| | - Janine R Shaw
- 1253 Fifield Hall, University of Florida, Gainesville, FL 32611, USA
| | | | - L Curtis Hannah
- 1253 Fifield Hall, University of Florida, Gainesville, FL 32611, USA.
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12
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Boehlein SK, Shaw JR, McCarty DR, Hwang SK, Stewart JD, Hannah LC. The potato tuber, maize endosperm and a chimeric maize-potato ADP-glucose pyrophosphorylase exhibit fundamental differences in Pi inhibition. Arch Biochem Biophys 2013; 537:210-6. [PMID: 23906662 DOI: 10.1016/j.abb.2013.07.019] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Revised: 07/09/2013] [Accepted: 07/16/2013] [Indexed: 10/26/2022]
Abstract
ADP-glucose pyrophosphorylase (AGPase) is highly regulated by allosteric effectors acting both positively and negatively. Enzymes from various sources differ, however, in the mechanism of allosteric regulation. Here, we determined how the effector, inorganic phosphate (Pi), functions in the presence and absence of saturating amounts of the activator, 3-phosphoglyceric acid (3-PGA). This regulation was examined in the maize endosperm enzyme, the oxidized and reduced forms of the potato tuber enzyme as well as a small subunit chimeric AGPase (MP), which contains both maize endosperm and potato tuber sequences paired with a wild-type maize large subunit. These data, combined with our previous kinetic studies of these enzymes led to a model of Pi inhibition for the various enzymes. The Pi inhibition data suggest that while the maize enzyme contains a single effector site that binds both 3-PGA and Pi, the other enzymes exhibit more complex behavior and most likely have at least two separate interacting binding sites for Pi. The possible physiological implications of the differences in Pi inhibition distinguishing the maize endosperm and potato tuber AGPases are discussed.
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Affiliation(s)
- Susan K Boehlein
- Program in Plant Molecular and Cellular Biology and Horticultural Sciences, University of Florida, 1253 Fifield Hall, Gainesville, FL 32611, USA
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