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Boehlein SK, Pfister B, Hennen-Bierwagen TA, Liu C, Ritter M, Hannah LC, Zeeman SC, Resende MFR, Myers AM. Soluble and insoluble α-glucan synthesis in yeast by enzyme suites derived exclusively from maize endosperm. Plant Physiol 2023; 193:1456-1478. [PMID: 37339339 PMCID: PMC10517254 DOI: 10.1093/plphys/kiad358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Revised: 04/28/2023] [Accepted: 05/23/2023] [Indexed: 06/22/2023]
Abstract
Molecular mechanisms that distinguish the synthesis of semi-crystalline α-glucan polymers found in plant starch granules from the synthesis of water-soluble polymers by nonplant species are not well understood. To address this, starch biosynthetic enzymes from maize (Zea mays L.) endosperm were isolated in a reconstituted environment using yeast (Saccharomyces cerevisiae) as a test bed. Ninety strains were constructed containing unique combinations of 11 synthetic transcription units specifying maize starch synthase (SS), starch phosphorylase (PHO), starch branching enzyme (SBE), or isoamylase-type starch debranching enzyme (ISA). Soluble and insoluble branched α-glucans accumulated in varying proportions depending on the enzyme suite, with ISA function stimulating distribution into the insoluble form. Among the SS isoforms, SSIIa, SSIII, and SSIV individually supported the accumulation of glucan polymer. Neither SSI nor SSV alone produced polymers; however, synergistic effects demonstrated that both isoforms can stimulate α-glucan accumulation. PHO did not support α-glucan production by itself, but it had either positive or negative effects on polymer content depending on which SS or a combination thereof was present. The complete suite of maize enzymes generated insoluble particles resembling native starch granules in size, shape, and crystallinity. Ultrastructural analysis revealed a hierarchical assembly starting with subparticles of approximately 50 nm diameter that coalesce into discrete structures of approximately 200 nm diameter. These are assembled into semi-crystalline α-glucan superstructures up to 4 μm in length filling most of the yeast cytosol. ISA was not essential for the formation of such particles, but their abundance was increased dramatically by ISA presence.
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Affiliation(s)
- Susan K Boehlein
- Horticultural Sciences Department, University of Florida, Gainesville, FL 32601, USA
| | - Barbara Pfister
- Institute of Molecular Plant Biology, ETH Zurich, Zurich 8092, Switzerland
| | - Tracie A Hennen-Bierwagen
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Chun Liu
- Institute of Molecular Plant Biology, ETH Zurich, Zurich 8092, Switzerland
| | - Maximilian Ritter
- Institute for Building Materials, Department of Civil, Environmental and Geomatic Engineering, ETH Zurich, Zurich 8093, Switzerland
| | - L Curtis Hannah
- Horticultural Sciences Department, University of Florida, Gainesville, FL 32601, USA
| | - Samuel C Zeeman
- Institute of Molecular Plant Biology, ETH Zurich, Zurich 8092, Switzerland
| | - Marcio F R Resende
- Horticultural Sciences Department, University of Florida, Gainesville, FL 32601, USA
| | - Alan M Myers
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
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Finegan C, Boehlein SK, Leach KA, Madrid G, Hannah LC, Koch KE, Tracy WF, Resende MFR. Genetic Perturbation of the Starch Biosynthesis in Maize Endosperm Reveals Sugar-Responsive Gene Networks. Front Plant Sci 2022; 12:800326. [PMID: 35211133 PMCID: PMC8861272 DOI: 10.3389/fpls.2021.800326] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Accepted: 12/27/2021] [Indexed: 05/28/2023]
Abstract
In maize, starch mutants have facilitated characterization of key genes involved in endosperm starch biosynthesis such as large subunit of AGPase Shrunken2 (Sh2) and isoamylase type DBE Sugary1 (Su1). While many starch biosynthesis enzymes have been characterized, the mechanisms of certain genes (including Sugary enhancer1) are yet undefined, and very little is understood about the regulation of starch biosynthesis. As a model, we utilize commercially important sweet corn mutations, sh2 and su1, to genetically perturb starch production in the endosperm. To characterize the transcriptomic response to starch mutations and identify potential regulators of this pathway, differential expression and coexpression network analysis was performed on near-isogenic lines (NILs) (wildtype, sh2, and su1) in six genetic backgrounds. Lines were grown in field conditions and kernels were sampled in consecutive developmental stages (blister stage at 14 days after pollination (DAP), milk stage at 21 DAP, and dent stage at 28 DAP). Kernels were dissected to separate embryo and pericarp from the endosperm tissue and 3' RNA-seq libraries were prepared. Mutation of the Su1 gene led to minimal changes in the endosperm transcriptome. Responses to loss of sh2 function include increased expression of sugar (SWEET) transporters and of genes for ABA signaling. Key regulators of starch biosynthesis and grain filling were identified. Notably, this includes Class II trehalose 6-phosphate synthases, Hexokinase1, and Apetala2 transcription factor-like (AP2/ERF) transcription factors. Additionally, our results provide insight into the mechanism of Sugary enhancer1, suggesting a potential role in regulating GA signaling via GRAS transcription factor Scarecrow-like1.
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Affiliation(s)
- Christina Finegan
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL, United States
- Horticultural Sciences Department, University of Florida, Gainesville, FL, United States
| | - Susan K. Boehlein
- Horticultural Sciences Department, University of Florida, Gainesville, FL, United States
| | - Kristen A. Leach
- Horticultural Sciences Department, University of Florida, Gainesville, FL, United States
| | - Gabriela Madrid
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL, United States
- Horticultural Sciences Department, University of Florida, Gainesville, FL, United States
| | - L. Curtis Hannah
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL, United States
- Horticultural Sciences Department, University of Florida, Gainesville, FL, United States
| | - Karen E. Koch
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL, United States
- Horticultural Sciences Department, University of Florida, Gainesville, FL, United States
| | - William F. Tracy
- Department of Agronomy, University of Wisconsin- Madison, Madison, WI, United States
| | - Marcio F. R. Resende
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL, United States
- Horticultural Sciences Department, University of Florida, Gainesville, FL, United States
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3
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Boehlein SK, Liu P, Webster A, Ribeiro C, Suzuki M, Wu S, Guan JC, Stewart JD, Tracy WF, Settles AM, McCarty DR, Koch KE, Hannah LC, Hennen-Bierwagen TA, Myers AM. Effects of long-term exposure to elevated temperature on Zea mays endosperm development during grain fill. Plant J 2019; 99:23-40. [PMID: 30746832 DOI: 10.1111/tpj.14283] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2018] [Revised: 01/22/2019] [Accepted: 01/23/2019] [Indexed: 05/28/2023]
Abstract
Cereal yields decrease when grain fill proceeds under conditions of prolonged, moderately elevated temperatures. Endosperm-endogenous processes alter both rate and duration of dry weight gain, but underlying mechanisms remain unclear. Heat effects could be mediated by either abnormal, premature cessation of storage compound deposition or accelerated implementation of normal development. This study used controlled environments to isolate temperature as the sole environmental variable during Zea mays kernel-fill, from 12 days after pollination to maturity. Plants subjected to elevated day, elevated night temperatures (38°C day, 28°C night (38/28°C])) or elevated day, normal night (38/17°C), were compared with those from controls grown under normal day and night conditions (28/17°C). Progression of change over time in endosperm tissue was followed to dissect contributions at multiple levels, including transcriptome, metabolome, enzyme activities, product accumulation, and tissue ultrastructure. Integrated analyses indicated that the normal developmental program of endosperm is fully executed under prolonged high-temperature conditions, but at a faster rate. Accelerated development was observed when both day and night temperatures were elevated, but not when daytime temperature alone was increased. Although transcripts for most components of glycolysis and respiration were either upregulated or minimally affected, elevated temperatures decreased abundance of mRNAs related to biosynthesis of starch and storage proteins. Further analysis of 20 central-metabolic enzymes revealed six activities that were reduced under high-temperature conditions, indicating candidate roles in the observed reduction of grain dry weight. Nonetheless, a striking overall resilience of grain filling in the face of elevated temperatures can be attributed to acceleration of normal endosperm development.
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Affiliation(s)
- Susan K Boehlein
- Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Peng Liu
- Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Ashley Webster
- Department of Agronomy, University of Wisconsin, Madison, WI, 53706, USA
| | - Camila Ribeiro
- Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Masaharu Suzuki
- Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Shan Wu
- Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Jiahn-Chou Guan
- Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Jon D Stewart
- Department of Chemistry, University of Florida, Gainesville, FL, 32611, USA
| | - William F Tracy
- Department of Agronomy, University of Wisconsin, Madison, WI, 53706, USA
| | - A Mark Settles
- Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Donald R McCarty
- Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Karen E Koch
- Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Larkin C Hannah
- Horticultural Sciences Department, University of Florida, Gainesville, FL, 32611, USA
| | - Tracie A Hennen-Bierwagen
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, 50011, USA
| | - Alan M Myers
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA, 50011, USA
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4
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Zhang J, Wu S, Boehlein SK, McCarty DR, Song G, Walley JW, Myers A, Settles AM. Maize defective kernel5 is a bacterial TamB homologue required for chloroplast envelope biogenesis. J Cell Biol 2019; 218:2638-2658. [PMID: 31235479 PMCID: PMC6683743 DOI: 10.1083/jcb.201807166] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [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: 07/23/2018] [Revised: 05/07/2019] [Accepted: 06/04/2019] [Indexed: 01/10/2023] Open
Abstract
Zhang et al. show that the maize dek5 locus is required for chloroplast envelope biogenesis and encodes a TamB-like protein. Bacterial TamB proteins facilitate insertion of β-barrel outer membrane proteins, indicating plastids have a conserved mechanism for envelope membrane biogenesis. Chloroplasts are of prokaryotic origin with a double-membrane envelope separating plastid metabolism from the cytosol. Envelope membrane proteins integrate chloroplasts with the cell, but envelope biogenesis mechanisms remain elusive. We show that maize defective kernel5 (dek5) is critical for envelope biogenesis. Amyloplasts and chloroplasts are larger and reduced in number in dek5 with multiple ultrastructural defects. The DEK5 protein is homologous to rice SSG4, Arabidopsis thaliana EMB2410/TIC236, and Escherichia coli tamB. TamB functions in bacterial outer membrane biogenesis. DEK5 is localized to the envelope with a topology analogous to TamB. Increased levels of soluble sugars in dek5 developing endosperm and elevated osmotic pressure in mutant leaf cells suggest defective intracellular solute transport. Proteomics and antibody-based analyses show dek5 reduces levels of Toc75 and chloroplast envelope transporters. Moreover, dek5 chloroplasts reduce inorganic phosphate uptake with at least an 80% reduction relative to normal chloroplasts. These data suggest that DEK5 functions in plastid envelope biogenesis to enable transport of metabolites and proteins.
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Affiliation(s)
- Junya Zhang
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL
| | - Shan Wu
- Horticultural Sciences Department, University of Florida, Gainesville, FL
| | - Susan K Boehlein
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL.,Horticultural Sciences Department, University of Florida, Gainesville, FL
| | - Donald R McCarty
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL.,Horticultural Sciences Department, University of Florida, Gainesville, FL
| | - Gaoyuan Song
- Plant Pathology and Microbiology, Iowa State University, Ames, IA
| | - Justin W Walley
- Plant Pathology and Microbiology, Iowa State University, Ames, IA
| | - Alan Myers
- Roy J. Carver Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA
| | - A Mark Settles
- Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL .,Horticultural Sciences Department, University of Florida, Gainesville, FL
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5
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Boehlein SK, Shaw JR, Hannah LC. Enhancement of Heat Stability and Kinetic Parameters of the Maize Endosperm ADP-Glucose Pyrophosphorylase by Mutagenesis of Amino Acids in the Small Subunit With High B Factors. Front Plant Sci 2018; 9:1849. [PMID: 30619417 PMCID: PMC6300691 DOI: 10.3389/fpls.2018.01849] [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] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Accepted: 11/29/2018] [Indexed: 06/09/2023]
Abstract
ADP-glucose pyrophosphorylase (AGPase) is an important enzyme in starch synthesis and previous studies showed that the heat lability of this enzyme is a determinant to starch synthesis in the maize endosperm and, in turn, seed yield. Here, amino acids in the AGPase endosperm small subunit with high B-factors were mutagenized and individual changes enhancing heat stability and/or kinetic parameters in an Escherichia coli expression system were chosen. Individual mutations were combined and analyzed. One triple mutant, here termed Bt2-BF, was chosen for further study. Combinations of this heat stable, 3-PGA-independent small subunit variant with large subunits also heat stable yielded complex patterns of heat stability and kinetic and allosteric properties. Interestingly, two of the three changes reside in a protein motif found only in AGPases that exhibit high sensitivity to 3-PGA. While not the 3-PGA binding site, amino acid substitutions in this region significantly alter 3-PGA activation kinetics.
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Affiliation(s)
- Susan K. Boehlein
- Genetics Institute, University of Florida, Gainesville, FL, United States
- Department of Horticultural Sciences, University of Florida, Gainesville, FL, United States
| | - Janine R. Shaw
- Genetics Institute, University of Florida, Gainesville, FL, United States
- Department of Horticultural Sciences, University of Florida, Gainesville, FL, United States
| | - L. Curtis Hannah
- Genetics Institute, University of Florida, Gainesville, FL, United States
- Department of Horticultural Sciences, University of Florida, Gainesville, FL, United States
- Plant Molecular and Cellular Biology, University of Florida, Gainesville, FL, United States
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6
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Boehlein SK, Shaw JR, Boehlein TJ, Boehlein EC, Hannah LC. Fundamental differences in starch synthesis in the maize leaf, embryo, ovary and endosperm. Plant J 2018; 96:595-606. [PMID: 30062763 DOI: 10.1111/tpj.14053] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Accepted: 07/23/2018] [Indexed: 05/25/2023]
Abstract
Enzymological and starch analyses of various ADP-glucose pyrophosphorylase (AGPase) null mutants point to fundamental differences in the pathways for starch synthesis in the maize leaf, embryo, ovary and endosperm. Leaf starch is synthesized via the AGPase encoded by the small and large subunits shown previously to be expressed at abundant levels in the leaf, whereas more than one AGPase isoform functions in the embryo and in the ovary. Embryo starch content is also dependent on genes functioning in the leaf and in the endosperm. AGPase encoded by shrunken-2 and brittle-2 synthesizes ~75% of endosperm starch. The gene, agpsemzm, previously shown to encode the small subunit expressed in the embryo, and agpllzm, the leaf large subunit gene, are here shown to encode the endosperm, plastid-localized AGPase. Loss of this enzyme does not reduce endosperm starch. Rather, the data suggest that AGPase-independent starch synthesis accounts for ~25% of endosperm starch. Three maize genes encode the small subunit of the AGPase. Data here show that the triple mutant lacking all three small subunits is lethal in early seed development but can be viable in both male and female gametes. Seed and plant viability is restored by any one of the three small subunit genes, including one previously thought to function only in the cytosol of the endosperm. Data herein also show the functionality of a fourth gene encoding the large subunit of this enzyme. Although adenosine diphosphate glucose pyrophosphorylase is shown here to be essential for maize viability, strong evidence for starch synthesis in the endosperm that is independent of this enzyme is also presented. Starch synthesis is distinct in the maize embryo, ovary, leaf and endosperm, and is coordinated among the various tissues.
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Affiliation(s)
- Susan K Boehlein
- Program in Plant Molecular and Cellular Biology, Genetics Institute and the Department of Horticultural Sciences, University of Florida, Gainesville, FL, 32611, USA
| | - Janine R Shaw
- Program in Plant Molecular and Cellular Biology, Genetics Institute and the Department of Horticultural Sciences, University of Florida, Gainesville, FL, 32611, USA
| | - Timothy J Boehlein
- Program in Plant Molecular and Cellular Biology, Genetics Institute and the Department of Horticultural Sciences, University of Florida, Gainesville, FL, 32611, USA
| | - Emily C Boehlein
- Program in Plant Molecular and Cellular Biology, Genetics Institute and the Department of Horticultural Sciences, University of Florida, Gainesville, FL, 32611, USA
| | - L Curtis Hannah
- Program in Plant Molecular and Cellular Biology, Genetics Institute and the Department of Horticultural Sciences, University of Florida, Gainesville, FL, 32611, USA
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Gustin JL, Boehlein SK, Shaw JR, Junior W, Settles AM, Webster A, Tracy WF, Hannah LC. Ovary abortion is prevalent in diverse maize inbred lines and is under genetic control. Sci Rep 2018; 8:13032. [PMID: 30158664 PMCID: PMC6115450 DOI: 10.1038/s41598-018-31216-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Accepted: 08/14/2018] [Indexed: 11/23/2022] Open
Abstract
Crop improvement programs focus on characteristics that are important for plant productivity. Typically genes underlying these traits are identified and stacked to create improved cultivars. Hence, identification of valuable traits for plant productivity is critical for plant improvement. Here we describe an important characteristic for maize productivity. Despite the fact mature maize ears are typically covered with kernels, we find that only a fraction of ovaries give rise to mature kernels. Non-developed ovaries degenerate while neighboring fertilized ovaries produce kernels that fill the ear. Abortion occurs throughout the ear, not just at the tip. We show that the fraction of aborted ovaries/kernels is genetically controlled and varies widely among maize lines, and low abortion genotypes are rare. Reducing or eliminating ovary abortion could substantially increase yield, making this characteristic a new target for selection in maize improvement programs.
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Affiliation(s)
- Jeffery L Gustin
- Program in Plant Molecular and Cellular Biology, Genetics Institute and Department of Horticultural Sciences, University of Florida, Gainesville, FL, 32611, USA.
| | - Susan K Boehlein
- Program in Plant Molecular and Cellular Biology, Genetics Institute and Department of Horticultural Sciences, University of Florida, Gainesville, FL, 32611, USA
| | - Janine R Shaw
- Program in Plant Molecular and Cellular Biology, Genetics Institute and Department of Horticultural Sciences, University of Florida, Gainesville, FL, 32611, USA
| | - Weschester Junior
- Florida Agricultural and Mechanical University, Tallahassee, FL, 32301, USA
| | - A Mark Settles
- Program in Plant Molecular and Cellular Biology, Genetics Institute and Department of Horticultural Sciences, University of Florida, Gainesville, FL, 32611, USA
| | - Ashley Webster
- Department of Agronomy, University of Wisconsin, Madison, WI, 53706, USA
| | - William F Tracy
- Department of Agronomy, University of Wisconsin, Madison, WI, 53706, USA
| | - L Curtis Hannah
- Program in Plant Molecular and Cellular Biology, Genetics Institute and Department of Horticultural Sciences, University of Florida, Gainesville, FL, 32611, USA
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8
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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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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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10
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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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11
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Urbanek C, Goodison S, Chang M, Porvasnik S, Sakamoto N, Li CZ, Boehlein SK, Rosser CJ. Detection of antibodies directed at M. hyorhinis p37 in the serum of men with newly diagnosed prostate cancer. BMC Cancer 2011; 11:233. [PMID: 21663671 PMCID: PMC3129326 DOI: 10.1186/1471-2407-11-233] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Accepted: 06/10/2011] [Indexed: 01/01/2023] Open
Abstract
Background Recent epidemiologic, genetic, and molecular studies suggest infection and inflammation initiate certain cancers, including cancers of the prostate. Over the past several years, our group has been studying how mycoplasmas could possibly initiate and propagate cancers of the prostate. Specifically, Mycoplasma hyorhinis encoded protein p37 was found to promote invasion of prostate cancer cells and cause changes in growth, morphology and gene expression of these cells to a more aggressive phenotype. Moreover, we found that chronic exposure of benign human prostate cells to M. hyorhinis resulted in significant phenotypic and karyotypic changes that ultimately resulted in the malignant transformation of the benign cells. In this study, we set out to investigate another potential link between mycoplasma and human prostate cancer. Methods We report the incidence of men with prostate cancer and benign prostatic hyperplasia (BPH) being seropositive for M. hyorhinis. Antibodies to M. hyorhinis were surveyed by a novel indirect enzyme-linked immunosorbent assay (ELISA) in serum samples collected from men presenting to an outpatient Urology clinic for BPH (N = 105) or prostate cancer (N = 114) from 2006-2009. Results A seropositive rate of 36% in men with BPH and 52% in men with prostate cancer was reported, thus leading us to speculate a possible connection between M. hyorhinis exposure with prostate cancer. Conclusions These results further support a potential exacerbating role for mycoplasma in the development of prostate cancer.
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Affiliation(s)
- Cydney Urbanek
- Department of Urology, The University of Florida, Gainesville, Florida, 32610, USA
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12
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Sippel KH, Venkatakrishnan B, Boehlein SK, Sankaran B, Quirit JG, Govindasamy L, Agbandje-McKenna M, Goodison S, Rosser CJ, McKenna R. Insights into Mycoplasma genitalium metabolism revealed by the structure of MG289, an extracytoplasmic thiamine binding lipoprotein. Proteins 2011; 79:528-36. [PMID: 21117240 PMCID: PMC3017431 DOI: 10.1002/prot.22900] [Citation(s) in RCA: 9] [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] [Indexed: 01/07/2023]
Abstract
Mycoplasma genitalium is one of the smallest organisms capable of self-replication and its sequence is considered a starting point for understanding the minimal genome required for life. MG289, a putative phosphonate substrate binding protein, is considered to be one of these essential genes. The crystal structure of MG289 has been solved at 1.95 Å resolution. The structurally identified thiamine binding region reveals possible mechanisms for ligand promiscuity. MG289 was determined to be an extracytoplasmic thiamine binding lipoprotein. Computational analysis, size exclusion chromatography, and small angle X-ray scattering indicates that MG289 homodimerizes in a concentration-dependant manner. Comparisons to the thiamine pyrophosphate binding homolog Cypl reveal insights into the metabolic differences between mycoplasmal species including identifying possible kinases for cofactor phosphorylation and describing the mechanism of thiamine transport into the cell. These results provide a baseline to build our understanding of the minimal metabolic requirements of a living organism.
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Affiliation(s)
- Katherine H. Sippel
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL 32610
| | | | - Susan K. Boehlein
- Program in Plant Molecular and Cellular Biology and Horticultural Sciences, University of Florida, Gainesville, FL 32610
| | - Banumathi Sankaran
- Berkeley Center for Structural Biology, Lawrence Berkeley Laboratory, Berkeley CA 94720
| | - Jeanne G. Quirit
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL 32610
| | - Lakshamanan Govindasamy
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL 32610
| | - Mavis Agbandje-McKenna
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL 32610
| | - Steve Goodison
- Department of Surgery Jacksonville, Shands Health Science Center, FL 32209, USA
| | | | - Robert McKenna
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL 32610,Correspondence to: Robert McKenna. Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL 32610. Phone: (352)392-5696. Fax: (352)392-3422.
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13
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Boehlein SK, Shaw JR, Stewart JD, Hannah LC. Studies of the kinetic mechanism of maize endosperm ADP-glucose pyrophosphorylase uncovered complex regulatory properties. Plant Physiol 2010; 152:1056-64. [PMID: 20018600 PMCID: PMC2815884 DOI: 10.1104/pp.109.149450] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
ADP-glucose pyrophosphorylase catalyzes the synthesis of ADP-glucose (ADP-Glc) from Glc-1-phosphate (G-1-P) and ATP. Kinetic studies were performed to define the nature of the reaction, both in the presence and absence of allosteric effector molecules. When 3-phosphoglycerate (3-PGA), the putative physiological activator, was present at a saturating level, initial velocity studies were consistent with a Theorell-Chance BiBi mechanism and product inhibition data supported sequential binding of ATP and G-1-P, followed by ordered release of pyrophosphate and ADP-Glc. A sequential mechanism was also followed when 3-PGA was absent, but product inhibition patterns changed dramatically. In the presence of 3-PGA, ADP-Glc is a competitive inhibitor with respect to ATP. In the absence of 3-PGA--with or without 5.0 mm inorganic phosphate--ADP-Glc actually stimulated catalytic activity, acting as a feedback product activator. By contrast, the other product, pyrophosphate, is a potent inhibitor in the absence of 3-PGA. In the presence of subsaturating levels of allosteric effectors, G-1-P serves not only as a substrate but also as an activator. Finally, in the absence of 3-PGA, inorganic phosphate, a classic inhibitor or antiactivator of the enzyme, stimulates enzyme activity at low substrate by lowering the K(M) values for both substrates.
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14
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Boehlein SK, Shaw JR, Hannah LC, Stewart JD. Probing allosteric binding sites of the maize endosperm ADP-glucose pyrophosphorylase. Plant Physiol 2010; 152:85-95. [PMID: 19889875 PMCID: PMC2799348 DOI: 10.1104/pp.109.146928] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Maize (Zea mays) endosperm ADP-glucose pyrophosphorylase (AGPase) is a highly regulated enzyme that catalyzes the rate-limiting step in starch biosynthesis. Although the structure of the heterotetrameric maize endosperm AGPase remains unsolved, structures of a nonnative, low-activity form of the potato tuber (Solanum tuberosum) AGPase (small subunit homotetramer) reported previously by others revealed that several sulfate ions bind to each enzyme. These sites are also believed to interact with allosteric regulators such as inorganic phosphate and 3-phosphoglycerate (3-PGA). Several arginine (Arg) side chains contact the bound sulfate ions in the potato structure and likely play important roles in allosteric effector binding. Alanine-scanning mutagenesis was applied to the corresponding Arg residues in both the small and large subunits of maize endosperm AGPase to determine their roles in allosteric regulation and thermal stability. Steady-state kinetic and regulatory parameters were measured for each mutant. All of the Arg mutants examined--in both the small and large subunits--bound 3-PGA more weakly than the wild type (A(50) increased by 3.5- to 20-fold). By contrast, the binding of two other maize AGPase allosteric activators (fructose-6-phosphate and glucose-6-phosphate) did not always mimic the changes observed for 3-PGA. In fact, compared to 3-PGA, fructose-6-phosphate is a more efficient activator in two of the Arg mutants. Phosphate binding was also affected by Arg substitutions. The combined data support a model for the binding interactions associated with 3-PGA in which allosteric activators and inorganic phosphate compete directly.
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15
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Sippel KH, Boehlein SK, Sakai Y, Quirit JG, Agbandje-McKenna M, Rosser CJ, McKenna R. Cloning, expression, purification, crystallization and preliminary X-ray analysis of Mycoplasma genitalium protein MG289. Acta Crystallogr Sect F Struct Biol Cryst Commun 2009; 65:910-2. [PMID: 19724130 DOI: 10.1107/s1744309109030565] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2009] [Accepted: 07/31/2009] [Indexed: 11/10/2022]
Abstract
Mycoplasma genitalium is a human pathogen that is associated with nongonococcal urethritis in men and cervicitis in women. The cloning, expression, purification and crystallization of the protein MG289 from M. genitalium strain G37 are reported here. Crystals of MG289 diffracted X-rays to 2.8 A resolution. The crystals belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 49.7, b = 90.9, c = 176.1 A. The diffraction data after processing had an overall R(merge) of 8.7%. The crystal structure of Cypl, the ortholog of MG289 from M. hyorhinis, has recently been determined, providing a reasonable phasing model; molecular replacement is currently under way.
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Affiliation(s)
- Katherine H Sippel
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
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16
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Sippel KH, Robbins AH, Reutzel R, Boehlein SK, Namiki K, Goodison S, Agbandje-McKenna M, Rosser CJ, McKenna R. Structural insights into the extracytoplasmic thiamine-binding lipoprotein p37 of Mycoplasma hyorhinis. J Bacteriol 2009; 191:2585-92. [PMID: 19233924 PMCID: PMC2668404 DOI: 10.1128/jb.01680-08] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2008] [Accepted: 02/09/2009] [Indexed: 01/07/2023] Open
Abstract
The Mycoplasma hyorhinis protein p37 has been implicated in tumorigenic transformation for more than 20 years. Though there are many speculations as to its function, based solely on sequence homology, the issue has remained unresolved. Presented here is the 1.6-A-resolution refined crystal structure of M. hyorhinis p37, renamed the extracytoplasmic thiamine-binding lipoprotein (Cypl). The structure shows thiamine pyrophosphate (TPP) and two calcium ions are bound to Cypl and give the first insights into possible functions of the Cypl-like family of proteins. Sequence alignments of Cypl-like proteins between several different species of mycoplasma show that the thiamine-binding site is likely conserved and structural alignments reveal the similarity of Cypl to various binding proteins. While the experimentally determined function of Cypl remains unknown, the structure shows that the protein is a TPP-binding protein, opening up many avenues for future mechanistic studies and making Cypl a possible target for combating mycoplasma infections and tumorigenic transformation.
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Affiliation(s)
- Katherine H Sippel
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL 32610, USA
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17
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Boehlein SK, Shaw JR, Stewart JD, Hannah LC. Characterization of an autonomously activated plant ADP-glucose pyrophosphorylase. Plant Physiol 2009; 149:318-26. [PMID: 18715954 PMCID: PMC2613723 DOI: 10.1104/pp.108.126862] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2008] [Accepted: 08/08/2008] [Indexed: 05/23/2023]
Abstract
ADP-glucose pyrophosphorylase (AGPase) catalyzes the rate-limiting step in starch biosynthesis in plants and changes in its catalytic and/or allosteric properties can lead to increased starch production. Recently, a maize (Zea mays)/potato (Solanum tuberosum) small subunit mosaic, MP [Mos(1-198)], containing the first 198 amino acids of the small subunit of the maize endosperm enzyme and the last 277 amino acids from the potato tuber enzyme, was expressed with the maize endosperm large subunit and was reported to have favorable kinetic and allosteric properties. Here, we show that this mosaic, in the absence of activator, performs like a wild-type AGPase that is partially activated with 3-phosphoglyceric acid (3-PGA). In the presence of 3-PGA, enzyme properties of Mos(1-198)/SH2 are quite similar to those of the wild-type maize enzyme. In the absence of 3-PGA, however, the mosaic enzyme exhibits greater activity, higher affinity for the substrates, and partial inactivation by inorganic phosphate. The Mos(1-198)/SH2 enzyme is also more stable to heat inactivation. The different properties of this protein were mapped using various mosaics containing smaller portions of the potato small subunit. Enhanced heat stability of Mos(1-198) was shown to originate from five potato-derived amino acids between 322 and 377. These amino acids were shown previously to be important in small subunit/large subunit interactions. These five potato-derived amino acids plus other potato-derived amino acids distributed throughout the carboxyl-terminal portion of the protein are required for the enhanced catalytic and allosteric properties exhibited by Mos(1-198)/SH2.
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Affiliation(s)
- Susan K Boehlein
- Program in Plant Molecular and Cellular Biology and Horticultural Sciences, University of Florida, Gainesville, Florida 32611-7200, USA
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18
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Sippel KH, Robbins AH, Reutzel R, Domsic J, Boehlein SK, Govindasamy L, Agbandje-McKenna M, Rosser CJ, McKenna R. Structure determination of the cancer-associated Mycoplasma hyorhinis protein Mh-p37. Acta Crystallogr D Biol Crystallogr 2008; 64:1172-8. [PMID: 19020356 DOI: 10.1107/s0907444908030175] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2008] [Accepted: 09/18/2008] [Indexed: 11/10/2022]
Abstract
The crystal structure of the Mycoplasma hyorhinis protein Mh-p37 has been solved and refined to 1.9 A resolution. This is the first de novo structure to be determined using the recently described heavy-atom reagent [Beck et al. (2008), Acta Cryst. D64, 1179-1182] 5-amino-2,4,6-triiodoisophthalic acid (I3C), which contains three I atoms arranged in an equilateral triangle, by SIRAS methods. Data collection was performed in-house at room temperature. SHELXD and SHELXE were used to determine the I-atom positions and phase the native protein and PHENIX AutoBuild software was used to automatically fit the amino-acid sequence to the electron-density map. The structure was refined using SHELX97 to an R(cryst) of 18.6% and an R(free) of 24.0%. Mh-p37 is an alpha/beta protein with two well defined domains which are separated by a deep cleft. An unanticipated ligand bound in the center of the molecule at the base of the cleft has been modeled as thiamine pyrophosphate or vitamin B(1). Retrospective attempts to solve the crystal structure by Patterson search methods using either isomorphous or anomalous differences failed. Additionally, attempts to use proteins with the highest structural homology in the Protein Data Bank to phase the data by molecular replacement were unsuccessful, most likely in hindsight because of their poor structural agreement. Therefore, the I3C reagent offers an alternative, quick and inexpensive method for in-house phasing of de novo structures where other methods may not be successful.
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Affiliation(s)
- Katherine H Sippel
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
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19
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Boehlein SK, Shaw JR, Stewart JD, Hannah LC. Heat stability and allosteric properties of the maize endosperm ADP-glucose pyrophosphorylase are intimately intertwined. Plant Physiol 2008; 146:289-99. [PMID: 18024561 PMCID: PMC2230563 DOI: 10.1104/pp.107.109942] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2007] [Accepted: 11/07/2007] [Indexed: 05/23/2023]
Abstract
ADP-glucose (Glc) pyrophosphorylase (AGPase), a key regulatory enzyme in starch biosynthesis, is highly regulated. Transgenic approaches in four plant species showed that alterations in either thermal stability or allosteric modulation increase starch synthesis. Here, we show that the classic regulators 3-phosphoglyceric acid (3-PGA) and inorganic phosphate (Pi) stabilize maize (Zea mays) endosperm AGPase to thermal inactivation. In addition, we show that glycerol phosphate and ribose-5-P increase the catalytic activity of maize AGPase to the same extent as the activator 3-PGA, albeit with higher K(a) (activation constant) values. Activation by fructose-6-P and Glc-6-P is comparable to that of 3-PGA. The reactants ATP and ADP-Glc, but not Glc-1-P and pyrophosphate, protect AGPase from thermal inactivation, a result consistent with the ordered kinetic mechanism reported for other AGPases. 3-PGA acts synergistically with both ATP and ADP-Glc in heat protection, decreasing the substrate concentration needed for protection and increasing the extent of protection. Characterization of a series of activators and inhibitors suggests that they all bind at the same site or at mutually exclusive sites. Pi, the classic "inhibitor" of AGPase, binds to the enzyme in the absence of other metabolites, as determined by thermal protections experiments, but does not inhibit activity. Rather, Pi acts by displacing bound activators and returning the enzyme to its activity in their absence. Finally, we show from thermal inactivation studies that the enzyme exists in two forms that have significantly different stabilities and do not interconvert rapidly.
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Affiliation(s)
- Susan K Boehlein
- Program in Plant Molecular and Cellular Biology and Horticultural Sciences, University of Florida, Gainesville, FL 32611-7200, USA
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20
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Goodison S, Nakamura K, Iczkowski KA, Anai S, Boehlein SK, Rosser CJ. Exogenous mycoplasmal p37 protein alters gene expression, growth and morphology of prostate cancer cells. Cytogenet Genome Res 2007; 118:204-13. [PMID: 18000372 DOI: 10.1159/000108302] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2007] [Accepted: 02/05/2007] [Indexed: 11/19/2022] Open
Abstract
We previously showed that the Mycoplasma hyorhinis-encoded protein p37 can promote invasion of cancer cells in a dose-dependent manner, an effect that was blocked by monoclonal antibodies specific for p37. In this study, we further elucidated changes in growth, morphology and gene expression in prostate cancer cell lines when treated with exogenous p37 protein. Incubation with recombinant p37 caused significant nuclear enlargement, denoting active, anaplastic cells and increased the migratory potential of both PC-3 and DU145 cells. Microarray analysis of p37-treated and untreated cells identified eight gene expression clusters that could be broadly classified into three basic patterns. These were an increase in both cell lines, a decrease in either cell line or a cell line-specific differential trend. The most represented functional gene categories included cell cycle, signal transduction and metabolic factors. Taken together, these observations suggest that p37 potentiates the aggressiveness of prostate cancer and thus molecular events triggered by p37 maybe target for therapy.
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Affiliation(s)
- S Goodison
- Department of Surgery, The University of Florida, Jacksonville, FL, USA
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21
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Abstract
Previous studies have shown a statistically significant correlation between human carcinomas and monoclonal antibody detection of a Mycoplasma hyorhinis-encoded protein known as p37. A potential mechanism of p37 is that it might promote invasion and metastasis. Recombinant p37 enhanced the invasiveness of two prostate carcinoma and two melanoma cell lines in a dose-dependent manner in vitro, but did not have a significant effect on tumor cell growth. Furthermore, the increased binding to cell surfaces and the enhanced invasive potential of cancer cells from exposure to p37 could be completely reversed by preincubation of the cancer cells with an anti-p37 monoclonal antibody. Sequence comparisons, followed by three-dimensional molecular modeling, revealed a region of similarity between p37 and influenza hemagglutinin A, a sialic acid-binding protein that plays a critical role in viral entry. Binding of p37 to prostate carcinoma cells was found to be at least partially sialic acid dependent because neuraminidase treatment decreased this binding. Taken together, these observations suggest that M. hyorhinis can infect humans and may facilitate tumor invasiveness via p37. These results further suggest that p37 may be a molecular target for cancer therapy.
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Affiliation(s)
- Catherine M Ketcham
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, 32610, USA
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Linebarger CRL, Boehlein SK, Sewell AK, Shaw J, Hannah LC. Heat stability of maize endosperm ADP-glucose pyrophosphorylase is enhanced by insertion of a cysteine in the N terminus of the small subunit. Plant Physiol 2005; 139:1625-34. [PMID: 16299180 PMCID: PMC1310547 DOI: 10.1104/pp.105.067637] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2005] [Revised: 09/11/2005] [Accepted: 09/13/2005] [Indexed: 05/05/2023]
Abstract
ADP-glucose pyrophosphorylase (AGPase) is a key regulatory enzyme in starch biosynthesis. However, plant AGPases differ in several parameters, including spatial and temporal expression, allosteric regulation, and heat stability. AGPases of cereal endosperms are heat labile, while those in other tissues, such as the potato (Solanum tuberosum) tuber, are heat stable. Sequence comparisons of heat-stable and heat-labile AGPases identified an N-terminal motif unique to heat-stable enzymes. Insertion of this motif into recombinant maize (Zea mays) endosperm AGPase increased the half-life at 58 degrees C more than 70-fold. Km values for physiological substrates were unaffected, although Kcat was doubled. A cysteine within the inserted motif gives rise to small subunit homodimers not found in the wild-type maize enzyme. Placement of this N-terminal motif into a mosaic small subunit containing the N terminus from maize endosperm and the C terminus from potato tuber AGPase increases heat stability more than 300-fold.
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Affiliation(s)
- Carla R Lyerly Linebarger
- Program in Plant Molecular and Cellular Biology and Horticultural Sciences, University of Florida, Gainesville, Florida 32610-0245, USA
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Boehlein SK, Sewell AK, Cross J, Stewart JD, Hannah LC. Purification and characterization of adenosine diphosphate glucose pyrophosphorylase from maize/potato mosaics. Plant Physiol 2005; 138:1552-62. [PMID: 15951484 PMCID: PMC1176425 DOI: 10.1104/pp.105.060699] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Adenosine diphosphate glucose pyrophosphorylase (AGPase) catalyzes a rate-limiting step in starch biosynthesis. The reaction produces ADP-glucose and pyrophosphate from glucose-1-P and ATP. Investigations from a number of laboratories have shown that alterations in allosteric properties as well as heat stability of this enzyme have dramatic positive effects on starch synthesis in the potato (Solanum tuberosum) tuber and seeds of important cereals. Here, we report the characterization of purified recombinant mosaic AGPases derived from protein motifs normally expressed in the maize (Zea mays) endosperm and the potato tuber. These exhibit properties that should be advantageous when expressed in plants. We also present an in-depth characterization of the kinetic and allosteric properties of these purified recombinant AGPases. These data point to previously unrecognized roles for known allosteric effectors.
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Affiliation(s)
- Susan K Boehlein
- Department of Biochemistry and Molecular Biology , University of Florida, Gainesville, Florida 32611, USA
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Cross JM, Clancy M, Shaw JR, Boehlein SK, Greene TW, Schmidt RR, Okita TW, Hannah LC. A polymorphic motif in the small subunit of ADP-glucose pyrophosphorylase modulates interactions between the small and large subunits. Plant J 2005; 41:501-511. [PMID: 15686515 DOI: 10.1111/j.1365-313x.2004.02315.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The heterotetrameric, allosterically regulated enzyme, adenosine-5'-diphosphoglucose pyrophosphorylase (AGPase) catalyzes the rate-limiting step in starch synthesis. Despite vast differences in allosteric properties and a long evolutionary separation, heterotetramers of potato small subunit and maize large subunit have activity comparable to either parent in an Escherichia coli expression system. In contrast, co-expression of maize small subunit with the potato large subunit produces little activity as judged by in vivo activity stain. To pinpoint the region responsible for differential activity, we expressed chimeric maize/potato small subunits in E. coli. This identified a 55-amino acid motif of the potato small subunit that is critical for glycogen production when expressed with the potato large subunit. Potato and maize small subunit sequences differ at five amino acids in this motif. Replacement experiments revealed that at least four amino acids of maize origin were required to reduce staining. An AGPase composed of a chimeric potato small subunit containing the 55-amino acid maize motif with the potato large subunit exhibited substantially less affinity for the substrates, glucose-1-phosphate and ATP and an increased Ka for the activator, 3-phosphoglyceric acid. Placement of the potato motif into the maize small subunit restored glycogen synthesis with the potato large subunit. Hence, a small polymorphic motif within the small subunit influences both catalytic and allosteric properties by modulating subunit interactions.
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Affiliation(s)
- Joanna M Cross
- Program in Plant Molecular and Cellular Biology and Horticultural Sciences, University of Florida, PO Box 110690, 2211 Fifield Hall, Gainesville, FL 32611, USA
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Schnizer HG, Boehlein SK, Stewart JD, Richards NGJ, Schuster SM. gamma-Glutamyl thioester intermediate in glutaminase reaction catalyzed by Escherichia coli asparagine synthetase B. Methods Enzymol 2003; 354:260-71. [PMID: 12418233 DOI: 10.1016/s0076-6879(02)54022-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/27/2023]
Affiliation(s)
- Holly G Schnizer
- Department of Biochemistry, University of Florida College of Medicine, Gainesville, Florida 32610, USA
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Reutzel R, Boehlein SK, Govindasamy L, Brenes RB, Agbandje-McKenna M, Schuster SM, McKenna R. Crystallization and preliminary X-ray analysis of the tumor metastasis factor p37. Acta Crystallogr D Biol Crystallogr 2002; 58:2141-4. [PMID: 12454480 DOI: 10.1107/s0907444902015536] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2002] [Accepted: 08/27/2002] [Indexed: 11/10/2022]
Abstract
P37, an outer-membrane bacterial protein from Mycoplasma hyorhinis, is a molecule whose presence on the surface of many tumor cells correlates highly with increased neoplastic invasivity and metastasis. P37 was overexpressed in Escherichia coli, purified by affinity chromatography and crystallized. Useful single crystals for X-ray diffraction structural studies have been grown by oil-immersion methods from a solution of 40% PEG 4000, 0.1 M ammonium bromide in a 0.1 M citrate buffer at pH 4.0. X-ray diffraction data were collected at the F2 beamline at CHESS with a crystal-to-CCD detector distance of 150 mm, collecting 1 degrees oscillation slices with an exposure time of 30 s per frame. A 212 degrees sweep of data (99.8% completeness) were collected from a single crystal under cryoconditions, with a maximal useful diffraction pattern to 1.8 A resolution. The crystals are shown to be monoclinic and have been assigned to space group P2(1), with unit-cell parameters a = 50.02, b = 67.26, c = 59.89 A, beta = 108.29 degrees and a scaling R(sym) of 0.076 for 34,882 unique reflections. Packing considerations indicate that there is one molecule per asymmetric unit. It is expected that in the near future the structure of p37 will be obtained using phases from traditional heavy-atom isomorphous replacement and/or halide-soak methods. Elucidation of the structure of p37 may be paramount to producing new antibody-based anticancer therapeutic agents.
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Affiliation(s)
- Robbie Reutzel
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
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27
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Boehlein SK, Nakatsu T, Hiratake J, Thirumoorthy R, Stewart JD, Richards NG, Schuster SM. Characterization of inhibitors acting at the synthetase site of Escherichia coli asparagine synthetase B. Biochemistry 2001; 40:11168-75. [PMID: 11551215 DOI: 10.1021/bi0155551] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Asparagine synthetase catalyzes the ATP-dependent formation of L-asparagine from L-aspartate and L-glutamine, via a beta-aspartyl-AMP intermediate. Since interfering with this enzyme activity might be useful for treating leukemia and solid tumors, we have sought small-molecule inhibitors of Escherichia coli asparagine synthetase B (AS-B) as a model system for the human enzyme. Prior work showed that L-cysteine sulfinic acid competitively inhibits this enzyme by interfering with L-aspartate binding. Here, we demonstrate that cysteine sulfinic acid is also a partial substrate for E. coli asparagine synthetase, acting as a nucleophile to form the sulfur analogue of beta-aspartyl-AMP, which is subsequently hydrolyzed back to cysteine sulfinic acid and AMP in a futile cycle. While cysteine sulfinic acid did not itself constitute a clinically useful inhibitor of asparagine synthetase B, these results suggested that replacing this linkage by a more stable analogue might lead to a more potent inhibitor. A sulfoximine reported recently by Koizumi et al. as a competitive inhibitor of the ammonia-dependent E. coli asparagine synthetase A (AS-A) [Koizumi, M., Hiratake, J., Nakatsu, T., Kato, H., and Oda, J. (1999) J. Am. Chem. Soc. 121, 5799-5800] can be regarded as such a species. We found that this sulfoximine also inhibited AS-B, effectively irreversibly. Unlike either the cysteine sulfinic acid interaction with AS-B or the sulfoximine interaction with AS-A, only AS-B productively engaged in asparagine synthesis could be inactivated by the sulfoximine; free enzyme was unaffected even after extended incubation with the sulfoximine. Taken together, these results support the notion that sulfur-containing analogues of aspartate can serve as platforms for developing useful inhibitors of AS-B.
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Affiliation(s)
- S K Boehlein
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, USA
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28
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Larsen TM, Boehlein SK, Schuster SM, Richards NG, Thoden JB, Holden HM, Rayment I. Three-dimensional structure of Escherichia coli asparagine synthetase B: a short journey from substrate to product. Biochemistry 1999; 38:16146-57. [PMID: 10587437 DOI: 10.1021/bi9915768] [Citation(s) in RCA: 162] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Asparagine synthetase B catalyzes the assembly of asparagine from aspartate, Mg(2+)ATP, and glutamine. Here, we describe the three-dimensional structure of the enzyme from Escherichia colidetermined and refined to 2.0 A resolution. Protein employed for this study was that of a site-directed mutant protein, Cys1Ala. Large crystals were grown in the presence of both glutamine and AMP. Each subunit of the dimeric protein folds into two distinct domains. The N-terminal region contains two layers of antiparallel beta-sheet with each layer containing six strands. Wedged between these layers of sheet is the active site responsible for the hydrolysis of glutamine. Key side chains employed for positioning the glutamine substrate within the binding pocket include Arg 49, Asn 74, Glu 76, and Asp 98. The C-terminal domain, responsible for the binding of both Mg(2+)ATP and aspartate, is dominated by a five-stranded parallel beta-sheet flanked on either side by alpha-helices. The AMP moiety is anchored to the protein via hydrogen bonds with O(gamma) of Ser 346 and the backbone carbonyl and amide groups of Val 272, Leu 232, and Gly 347. As observed for other amidotransferases, the two active sites are connected by a tunnel lined primarily with backbone atoms and hydrophobic and nonpolar amino acid residues. Strikingly, the three-dimensional architecture of the N-terminal domain of asparagine synthetase B is similar to that observed for glutamine phosphoribosylpyrophosphate amidotransferase while the molecular motif of the C-domain is reminiscent to that observed for GMP synthetase.
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Affiliation(s)
- T M Larsen
- Department of Biochemistry, University of Wisconsin, Madison 53706, USA
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29
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Schnizer HG, Boehlein SK, Stewart JD, Richards NG, Schuster SM. Formation and isolation of a covalent intermediate during the glutaminase reaction of a class II amidotransferase. Biochemistry 1999; 38:3677-82. [PMID: 10090755 DOI: 10.1021/bi981450v] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Incubation of Escherichia coli asparagine synthetase B (AS-B) with [14C]-L-glutamine gives a covalent adduct that can be isolated. Radiolabeled protein is not observed (i) when the wild-type enzyme is incubated with 6-diazo-5-oxo-L-norleucine (DON) prior to reaction with [14C]glutamine or (ii) when the C1A AS-B mutant is incubated with [14C]-L-glutamine. Both of these alterations eliminate the ability of the enzyme to utilize glutamine but do not affect ammonia-dependent asparagine synthesis. Formation of the covalent adduct therefore depends on the presence of the N-terminal active site cysteine, which has been shown to be essential for glutamine-dependent activity in this and other class II amidotransferases. The amount of covalent adduct exhibits saturation behavior with increasing concentrations of L-glutamine. The maximum observed quantity of this intermediate is consistent with its involvement on the main pathway of glutamine hydrolysis. The chemical properties of the isolable covalent adduct are consistent with those anticipated for the gamma-glutamyl thioester that has been proposed as an intermediate in the AS-B-catalyzed conversion of glutamine to glutamate. The covalent adduct is acid-stable but is labile under alkaline conditions. On the basis of the measured rates of formation and breakdown of this intermediate, it is kinetically competent to participate in the normal catalytic mechanism. These studies represent the first description of a thioester intermediate for any class II amidotransferase and represent an important step in gaining further insight into the kinetic and chemical mechanisms of AS-B.
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Affiliation(s)
- H G Schnizer
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
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30
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Boehlein SK, Stewart JD, Walworth ES, Thirumoorthy R, Richards NG, Schuster SM. Kinetic mechanism of Escherichia coli asparagine synthetase B. Biochemistry 1998; 37:13230-8. [PMID: 9748330 DOI: 10.1021/bi981058h] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Escherichia coli asparagine synthetase B (AS-B) catalyzes the synthesis of asparagine from aspartate, glutamine, and ATP. A combination of kinetic, isotopic-labeling, and stoichiometry studies have been performed to define the nature of nitrogen transfer mediated by AS-B. The results of initial rate studies were consistent with initial binding and hydrolysis of glutamine to glutamate plus enzyme-bound ammonia. The initial velocity results were equally consistent with initial binding of ATP and aspartate prior to glutamine binding. However, product inhibition studies were only consistent with the latter pathway. Moreover, isotope-trapping studies confirmed that the enzyme-ATP-aspartate complex was kinetically competent. Studies using 18O-labeled aspartate were consistent with formation of a beta-aspartyl-AMP intermediate, and stoichiometry studies revealed that 1 equiv of this intermediate formed on the enzyme in the absence of a nitrogen source. Taken together, our results are most consistent with initial formation of beta -aspartyl-AMP intermediate prior to glutamine binding. This sequence leaves open many possibilities for the chemical mechanism of nitrogen transfer.
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Affiliation(s)
- S K Boehlein
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville 32610, USA
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31
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Boehlein SK, Walworth ES, Schuster SM. Identification of cysteine-523 in the aspartate binding site of Escherichia coli asparagine synthetase B. Biochemistry 1997; 36:10168-77. [PMID: 9254614 DOI: 10.1021/bi970494l] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The site-directed chemical modifier [p-(fluorosulfonyl)benzoyl]adenosine (5'-FSBA) inactivates Escherichia coli asparagine synthetase B activity following pseudo-first-order kinetics, with ATP providing specific protection, with a Kd of 12 microM. The 5'-FSBA modification appears to be covalent, even though a nonstoichiometric amount (less than 10%) of radiolabeled 5'-FSBA was associated with a totally inactivated enzyme. However, the inactivation by 5'-FSBA could be reversed upon the addition of dithiothreitol. These results are indicative of 5'-FSBA-induced disulfide bond formation, which requires the presence of at least two cysteine residues in the proximity of the ATP binding site. Identification of the critical cysteine residue was accomplished by sequential replacement of each cysteine in the protein by site-directed mutagenesis. Cys 523 was identified as the key residue involved in the formation of the 5'-FSBA-induced disulfide bond. Detailed kinetic analyses and comparison with similar enzymes, suggest that this cysteine residue, while in close proximity to the ATP binding site, is actually involved in aspartate binding in asparagine synthetase B.
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Affiliation(s)
- S K Boehlein
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
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32
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Boehlein SK, Rosa-Rodriguez JG, Schuster SM, Richards NGJ. Catalytic Activity of the N-Terminal Domain of Escherichia coli Asparagine Synthetase B Can Be Reengineered by Single-Point Mutation. J Am Chem Soc 1997. [DOI: 10.1021/ja9613668] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Susan K. Boehlein
- Contribution from the Department of Chemistry, University of Florida, Gainesville, Florida 32611, Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, and Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, Florida 32611
| | - José G. Rosa-Rodriguez
- Contribution from the Department of Chemistry, University of Florida, Gainesville, Florida 32611, Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, and Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, Florida 32611
| | - Sheldon M. Schuster
- Contribution from the Department of Chemistry, University of Florida, Gainesville, Florida 32611, Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, and Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, Florida 32611
| | - Nigel G. J. Richards
- Contribution from the Department of Chemistry, University of Florida, Gainesville, Florida 32611, Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, Florida 32610, and Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, Florida 32611
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33
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Boehlein SK, Walworth ES, Richards NG, Schuster SM. Mutagenesis and chemical rescue indicate residues involved in beta-aspartyl-AMP formation by Escherichia coli asparagine synthetase B. J Biol Chem 1997; 272:12384-92. [PMID: 9139684 DOI: 10.1074/jbc.272.19.12384] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Site-directed mutagenesis and kinetic studies have been employed to identify amino acid residues involved in aspartate binding and transition state stabilization during the formation of beta-aspartyl-AMP in the reaction mechanism of Escherichia coli asparagine synthetase B (AS-B). Three conserved amino acids in the segment defined by residues 317-330 appear particularly crucial for enzymatic activity. For example, when Arg-325 is replaced by alanine or lysine, the resulting mutant enzymes possess no detectable asparagine synthetase activity. The catalytic activity of the R325A AS-B mutant can, however, be restored to about 1/6 of that of wild-type AS-B by the addition of guanidinium HCl (GdmHCl). Detailed kinetic analysis of the rescued activity suggests that Arg-325 is involved in stabilization of a pentacovalent intermediate leading to the formation beta-aspartyl-AMP. This rescue experiment is the second example in which the function of a critical arginine residue that has been substituted by mutagenesis is restored by GdmHCl. Mutation of Thr-322 and Thr-323 also produces enzymes with altered kinetic properties, suggesting that these threonines are involved in aspartate binding and/or stabilization of intermediates en route to beta-aspartyl-AMP. These experiments are the first to identify residues outside of the N-terminal glutamine amide transfer domain that have any functional role in asparagine synthesis.
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Affiliation(s)
- S K Boehlein
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610, USA
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34
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Parr IB, Boehlein SK, Dribben AB, Schuster SM, Richards NGJ. Mapping the Aspartic Acid Binding Site of Escherichia coli Asparagine Synthetase B Using Substrate Analogs. J Med Chem 1996. [DOI: 10.1021/jm960598e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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35
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Parr IB, Boehlein SK, Dribben AB, Schuster SM, Richards NG. Mapping the aspartic acid binding site of Escherichia coli asparagine synthetase B using substrate analogs. J Med Chem 1996; 39:2367-78. [PMID: 8691431 DOI: 10.1021/jm9601009] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Novel inhibitors of asparagine synthetase, that will lower circulating levels of blood asparagine, have considerable potential in developing new protocols for the treatment of acute lymphoblastic leukemia. We now report the indirect characterization of the aspartate binding site of Escherichia coli asparagine synthetase B (AS-B) using a number of stereochemically, and conformationally, defined aspartic acid analogs. Two compounds, prepared using novel reaction conditions for the stereospecific beta-functionalization of aspartic acid diesters, have been found to be competitive inhibitors with respect to aspartate in kinetic studies on AS-B. Chemical modification experiments employing [(fluorosulfonyl)benzoyl]adenosine (FSBA), an ATP analog, demonstrate that both inhibitors bind to the aspartate binding site of AS-B. Our results reveal that large steric alterations in the substrate are not tolerated by the enzyme, consistent with the failure of previous efforts to develop AS inhibitors using random screening approaches, and that all of the ionizable groups are placed in close proximity in the bound conformation of aspartate.
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Affiliation(s)
- I B Parr
- Department of Chemistry, University of Florida, Gainesville 32611, USA
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36
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Stoker PW, O'Leary MH, Boehlein SK, Schuster SM, Richards NG. Probing the mechanism of nitrogen transfer in Escherichia coli asparagine synthetase by using heavy atom isotope effects. Biochemistry 1996; 35:3024-30. [PMID: 8608141 DOI: 10.1021/bi952504t] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In experiments aimed at determining the mechanism of nitrogen transfer in purF amidotransferase enzymes, 13C and 15N kinetic isotope effects have been measured for both of the glutamine-dependent activities of Escherichia coli asparagine synthetase B (AS-B). For the glutaminase reaction catalyzed by AS-B at pH 8.0, substitution heavy atom labels in the side chain amide of the substrate yields observed values of 1.0245 and 1.0095 for the amide carbon and amide nitrogen isotope effects, respectively. In the glutamine-dependent synthesis of asparagine at pH 8.0, the amide carbon and amide nitrogen isotope effects have values of 1.0231 and 1.0222, respectively. We interpret these results to mean that nitrogen transfer does not proceed by the formation of free ammonia in the active site of the enzyme and probably involves a series of intermediates in which glutamine becomes covalently attached to aspartate. While a number of mechanisms are consistent with the observed isotope effects, a likely reaction pathway involves reaction of an oxyanion with beta-aspartyl-AMP. This yields an intermediate in which C-N bond cleavage gives an acylthioenzyme and a second tetrahedral intermediate. Loss of AMP from the latter gives asparagine. An alternate reaction mechanism in which asparagine is generated from an imide intermediate also appears consistent with the observed kinetic isotope effects.
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Affiliation(s)
- P W Stoker
- Department of Biochemistry, Beadle Center, University of Nebraska-Lincoln, 68583, USA
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37
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Boehlein SK, Schuster SM, Richards NG. Glutamic acid gamma-monohydroxamate and hydroxylamine are alternate substrates for Escherichia coli asparagine synthetase B. Biochemistry 1996; 35:3031-7. [PMID: 8608142 DOI: 10.1021/bi952505l] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Escherichia coli asparagine synthetase B (AS-B) catalyzes the synthesis of asparagine from aspartic acid and glutamine in an ATP-dependent reaction. The ability of this enzyme to employ hydroxylamine and L-glutamic acid gamma-monohydroxamate (LGH) as alternative substrates in place of ammonia and L-glutamine, respectively, has been investigated. The enzyme is able to function as an amidohydrolase, liberating hydroxylamine from LGH with high catalytic efficiency, as measured by k(cat)/K(M). In addition, the kinetic parameters determined for hydroxylamine in AS-B synthetase activity are very similar to those of ammonia. Nitrogen transfer from LGH to yield aspartic acid beta-monohydroxamate is also catalyzed by AS-B. While such an observation has been made for a few members of the trpG amidotransferase family, our results appear to be the first demonstration that nitrogen transfer can occur from glutamine analogs in a purF amidotransferase. However, k(cat)/K(M) for the ATP-dependent transfer of hydroxylamine from LGH to aspartic acid is reduced 3-fold relative to that for glutamine-dependent asparagine synthesis. Further, the AS-B mutant in which asparagine is replaced by alanine (N74A) can also use hydroxylamine as an alternate substrate to ammonia and catalyze the hydrolysis of LGH. The catalytic efficiencies (k(cat)/K(M)) of nitrogen transfer from LGH and L-glutamine to beta-aspartyl-AMP are almost identical for the N74A AS-B mutant. These observations support the proposal that Asn-74 plays a role in catalyzing glutamine-dependent nitrogen transfer. We interpret our kinetic data as further evidence against ammonia-mediated nitrogen transfer from glutamine in the purF amidotransferase AS-B. These results are consistent with two alternate chemical mechanisms that have been proposed for this reaction [Boehlein, S. K., Richards, N. G. J., Walworth, E. S., & Schuster, S. M. (1994) J. Biol. Chem. 269, 26789-26795].
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Affiliation(s)
- S K Boehlein
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, 32610, USA
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38
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Boehlein SK, Richards NG, Walworth ES, Schuster SM. Arginine 30 and asparagine 74 have functional roles in the glutamine dependent activities of Escherichia coli asparagine synthetase B. J Biol Chem 1994; 269:26789-95. [PMID: 7929415] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Although Arg-30, Asn-74, and Asn-79 appear totally conserved throughout the purF glutamine-dependent amidotransferases, their potential roles in catalysis and binding remain unexplored for any member of the enzyme family. Here we report the overexpression, purification, and kinetic characterization of a series of AS-B mutants which allow an examination of the functional roles of these 3 residues in glutamine-dependent nitrogen transfer. While Asn-79 appears to possess no catalytic function in AS-B, site-directed mutagenesis of Asn-74 has implicated this residue as playing a role in catalysis of nitrogen transfer from glutamine. The kinetic properties of the Asn-74 AS-B mutant enzymes appear consistent with both ammonia-mediated nitrogen transfer and two apparently novel mechanistic suggestions for this reaction involving either an oxyanion or imide intermediate (Richards, N. G. J., and Schuster, S. M. (1992) FEBS Lett. 313, 98-102). We also demonstrate that replacement of Arg-30 by an alanine residue yields an AS-B mutant for which the apparent Km for glutamine is increased in the glutamine-dependent synthesis of asparagine. In addition, ATP-dependent stimulation of the glutaminase activity of AS-B is modified or completely eliminated when Arg-30 is replaced by other amino acids. The latter observation may indicate the existence of a molecular switch involving Arg-30 which coordinates the two half-reactions catalyzed by the glutamine-dependent amidotransferases and synthetase domains of cellular AS-B.
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Affiliation(s)
- S K Boehlein
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville 32610
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39
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Boehlein SK, Richards NG, Walworth ES, Schuster SM. Arginine 30 and asparagine 74 have functional roles in the glutamine dependent activities of Escherichia coli asparagine synthetase B. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)47088-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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40
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Boehlein SK, Richards NG, Schuster SM. Glutamine-dependent nitrogen transfer in Escherichia coli asparagine synthetase B. Searching for the catalytic triad. J Biol Chem 1994; 269:7450-7. [PMID: 7907328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The mechanism of nitrogen transfer in glutamine-dependent amidotransferases remains to be unambiguously established. We now report the overexpression, purification, and kinetic characterization of both the glutamine- and ammonia-dependent activities of Escherichia coli asparagine synthetase B (AS-B) and a series of mutants. In common with other members of the purF family of amidotransferases, the recombinant enzyme possesses an NH2-terminal cysteine residue. Replacement of Cys-1 by either alanine or serine results in a loss of glutaminase and glutamine-dependent activity, without out any significant effect upon ammonia-dependent asparagine synthesis. As previously observed for human AS (Sheng, S., Moraga-Amador, D., Van Heeke, G., Allison, R. D., Richards, N. G. J., and Schuster, S. M. (1993) J. Biol. Chem. 268, 16771-16780), glutamine is an inhibitor of the ammonia-dependent reaction catalyzed by both the Cys-1-->Ala (C1A) and Cys-1-->Ser (C1S) mutants of AS-B. In the case of C1A, the inhibition pattern suggests that an abortive complex is formed. This is consistent with a recent proposal implicating the formation of an imide intermediate in the nitrogen transfer reaction (Richards, N. G. J., and Schuster, S. M. (1992) FEBS Lett. 313, 98-102). In contrast, glutamine appears to be only a competitive inhibitor of the ammonia-dependent activity of C1S. Cys-1 does not appear to be required for glutamine binding. Replacement of Asp-33 by either asparagine or glutamic acid has little effect on the kinetic properties of the mutant enzymes when compared to wild-type AS-B. Cys-1 and Asp-33 are cognate to residues Cys-1 and Asp-29 in glutamine phosphoribosylpyrophosphate amidotransferase which have been proposed to be members of a catalytic triad responsible for mediating nitrogen transfer in this enzyme (Mei, B., and Zalkin, H. (1989) J. Biol. Chem. 264, 16613-16619). In the case of AS-B, although Cys-1 is essential for glutamine-dependent activity, Asp-33 does not appear to participate in mediating nitrogen transfer. In an effort to locate other residues which might form part of a "catalytic triad" in the glutamine amidotransferase domain of AS-B, we have expressed and characterized mutant proteins in which His-29 and His-80, which are conserved within the glutamine amidotransferase domain of purF amidotransferases, are replaced by alanine (H29A and H80A).(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- S K Boehlein
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville 32610
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