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Mark S. Hargrove - One of the best experts on this subject based on the ideXlab platform.
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review correlations between oxygen affinity and sequence classifications of plant hemoglobins
Biopolymers, 2009Co-Authors: Benoit J Smagghe, Gautam Sarath, Suman Kundu, Mark S. Hargrove, Ryan Percifield, Jeanlouis Hilbert, Richard A Watts, Elizabeth S Dennis, James W PeacockAbstract:Plants express three phylogenetic classes of hemoglobins (Hb) based on sequence analyses. Class 1 and 2 Hbs are full-length globins with the classical eight helix Mb-like fold, whereas Class 3 plant Hbs resemble the truncated globins found in bacteria. With the exception of the specialized Leghemoglobins, the physiological functions of these plant hemoglobins remain unknown. We have reviewed and, in some cases, measured new oxygen binding properties of a large number of Class 1 and 2 plant nonsymbiotic Hbs and Leghemoglobins. We found that sequence classification correlates with distinct extents of hexacoordination with the distal histidine and markedly different overall oxygen affinities and association and dissociation rate constants. These results suggest strong selective pressure for the evolution of distinct physiological functions. The Leghemoglobins evolved from the Class 2 globins and show no hexacoordination, very high rates of O2 binding
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Tyrosine B10 Inhibits Stabilization of Bound Carbon Monoxide and Oxygen in Soybean Leghemoglobin
Biochemistry, 2004Co-Authors: Suman Kundu, Gautam Sarath, George C. Blouin, Scott A. Premer, John S. Olson, Mark S. HargroveAbstract:Detailed comparisons of the carbon monoxide FTIR spectra and ligand-binding properties of a library of E7, E11, and B 10 mutants indicate significant differences in the role of electrostatic interactions in the distal pockets of wild-type sperm whale myoglobin and soybean Leghemoglobin. In myoglobin, strong hydrogen bonds from several closely related conformations of the distal histidine (His E 7 ) side chain preferentially stabilize bound oxygen. In Leghemoglobin, the imidazole side chain of His E 7 is confined to a single conformation, which only weakly hydrogen bonds to bound ligands. The phenol side chain of Tyr B 1 0 appears to "fix" the position of His E 7 , probably by donating a hydrogen bond to the Nδ atom of the imidazole side chain. The proximal pocket of Leghemoglobin is designed to favor strong coordination bonds between the heme iron and axial ligands. Thus, high oxygen affinity in Leghemoglobin is established by a favorable staggered geometry of the proximal histidine. The interaction between His E 7 and Tyr B 1 0 prevents overstabilization of bound oxygen. If hydrogen bonding from His E 7 were as strong as it is in mammalian myoglobin, the resultant ultrahigh affinity of Leghemoglobin would prevent oxygen transport in root nodules.
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Distal heme pocket regulation of ligand binding and stability in soybean Leghemoglobin
Proteins, 2003Co-Authors: Suman Kundu, Mark S. HargroveAbstract:Leghemoglobins facilitate diffusion of oxygen through root tissue to a bacterial terminal oxidase in much the same way that myoglobin transports oxygen from blood to muscle cell mitochondria. Leghemoglobin serves an additional role as an oxygen scavenger to prevent inhibition of nitrogen fixation. For this purpose, the oxygen affinity of soybean Leghemoglobin is 20-fold greater than myoglobin, resulting from an 8-fold faster association rate constant combined with a 3-fold slower dissociation rate constant. Although the biochemical mechanism used by myoglobin to bind oxygen has been described in elegant detail, an explanation for the difference in affinity between these two structurally similar proteins is not obvious. The present work demonstrates that, despite their similar structures, Leghemoglobin uses methods different from myoglobin to regulate ligand affinity. Oxygen and carbon monoxide binding to a comprehensive set of Leghemoglobin distal heme pocket mutant proteins in comparison to their myoglobin counterparts has revealed some of these mechanisms. The "distal histidine" provides a crucial hydrogen bond to stabilize oxygen in myoglobin but has little effect on bound oxygen in Leghemoglobin and is retained mainly for reasons of protein stability and prevention of heme loss. Furthermore, soybean Leghemoglobin uses an unusual combination of HisE7 and TyrB10 to sustain a weak stabilizing interaction with bound oxygen. Thus, the Leghemoglobin distal heme pocket provides a much lower barrier to oxygen association than occurs in myoglobin and oxygen dissociation is regulated from the proximal heme pocket.
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A Comparative Femtosecond Coherence Study of the Unligated Monomeric Hemeproteins Myoglobin and Leghemoglobin
The Journal of Physical Chemistry B, 2003Co-Authors: Mintu Halder, Mark S. Hargrove, Kaustuv Das, Pramit K. Chowdhury, Sangita Kundu, Jacob W. PetrichAbstract:Impulsive optical excitation has been performed on wild type, unligated Leghemoglobin for the first time to compare the induced vibrational coherence with that observed in myoglobin. Both proteins were excited at the Soret maxima and probed at red and blue edges of the Soret band. The resulting kinetic traces were modulated by low-frequency vibrations. Leghemoglobin shows a decrease in vibrational amplitude compared with myoglobin. The possible cause for the amplitude differences is discussed in terms of contributions from both ground- and excited-state vibrational coherences and ground-state heterogeneity.
Robert V. Klucas - One of the best experts on this subject based on the ideXlab platform.
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Flavin-mediated reduction of ferric Leghemoglobin from soybean nodules*
2016Co-Authors: Manuel Becana, Marvin L. Salin, Robert V. KlucasAbstract:Abbreviations and terminology: FLbR = ferric Leghemoglobin reductase; Hb2+/Hb3+ = hemoglobin containing Fe2+/Fe3+; Lb2+/Lb3+ = Leghemoglobin containing Fe2+/Fe3+; Lb3+.nicotinate/acetate = Lb in which nicotinate or acetate are complexed to Lb3+; Lb2+.O2/CO/NO / nicotinate = Lb in which O2, CO, NO or nicotinate are complexed to Lb2+; Rfl = riboflavin; SOD = superoxide dismutase (E
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Purification and Characterization of Soybean Root Nodule Ferric Leghemoglobin Reductase
Plant physiology, 1991Co-Authors: Stephen Wood, Manuel Becana, Robert V. KlucasAbstract:A ferric Leghemoglobin reductase from the cytosol of soybean (Glycine max) root nodules was purified to homogeneity and partially characterized. The enzyme is a flavoprotein with flavin adenine dinucleotide as the prosthetic group and consists of two identical subunits, each having a molecular mass of 54 kilodaltons. The pure enzyme shows a high activity for ferric Leghemoglobin reduction with NADH as the reductant in the absence of any exogenous mediators. The enzyme also exhibits NADH-dependent 2,6-dichloroindophenol reductase activity. A sequence of the first 50 N-terminal amino acids of the purified protein was obtained. Comparisons with known protein sequences have shown that the sequence of the ferric Leghemoglobin reductase is highly related to those of the flavin-nucleotide disulfide oxido-reductases, especially dihydrolipoamide dehydrogenase of the pyruvate dehydrogenase complex.
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Nicotinate, Nicotinamide, and the Reactivity of Leghemoglobin in Soybean Root Nodules
Plant Physiology, 1991Co-Authors: Robert V. Klucas, Cyril A. ApplebyAbstract:Nicotinate has been postulated to interfere with the binding of O2 to ferrous Leghemoglobin in soybean (Glycine max) root nodules. For such a function, the levels of nicotinate in nodules must be sufficiently high to bind a significant amount of Leghemoglobin. We have measured levels of nicotinate, nicotinamide, and Leghemoglobin in soybean nodules from plants 34 to 73 days after planting in a glasshouse. On a per gram nodule fresh weight basis, levels between 10.4 and 21 nanomoles for nicotinate, 19.2 and 37.8 nanomoles for nicotinamide, and 170 to 280 nanomoles for Leghemoglobin were measured. Even if all the nicotinate were bound to ferrous Leghemoglobin, only 11% or less of the total Leghemoglobin would be unavailable for binding O2. Using the measured levels of nicotinate and a pH of 6.8 in the cytosol of presenescent soybean nodules, we estimate that the proportion of ferrous Leghemoglobin bound to nicotinate in such nodules would be less than 1%. These levels of nicotinate are too low to interfere with the reaction between ferrous Leghemoglobin and O2 in soybean root nodules.
Suman Kundu - One of the best experts on this subject based on the ideXlab platform.
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review correlations between oxygen affinity and sequence classifications of plant hemoglobins
Biopolymers, 2009Co-Authors: Benoit J Smagghe, Gautam Sarath, Suman Kundu, Mark S. Hargrove, Ryan Percifield, Jeanlouis Hilbert, Richard A Watts, Elizabeth S Dennis, James W PeacockAbstract:Plants express three phylogenetic classes of hemoglobins (Hb) based on sequence analyses. Class 1 and 2 Hbs are full-length globins with the classical eight helix Mb-like fold, whereas Class 3 plant Hbs resemble the truncated globins found in bacteria. With the exception of the specialized Leghemoglobins, the physiological functions of these plant hemoglobins remain unknown. We have reviewed and, in some cases, measured new oxygen binding properties of a large number of Class 1 and 2 plant nonsymbiotic Hbs and Leghemoglobins. We found that sequence classification correlates with distinct extents of hexacoordination with the distal histidine and markedly different overall oxygen affinities and association and dissociation rate constants. These results suggest strong selective pressure for the evolution of distinct physiological functions. The Leghemoglobins evolved from the Class 2 globins and show no hexacoordination, very high rates of O2 binding
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Tyrosine B10 Inhibits Stabilization of Bound Carbon Monoxide and Oxygen in Soybean Leghemoglobin
Biochemistry, 2004Co-Authors: Suman Kundu, Gautam Sarath, George C. Blouin, Scott A. Premer, John S. Olson, Mark S. HargroveAbstract:Detailed comparisons of the carbon monoxide FTIR spectra and ligand-binding properties of a library of E7, E11, and B 10 mutants indicate significant differences in the role of electrostatic interactions in the distal pockets of wild-type sperm whale myoglobin and soybean Leghemoglobin. In myoglobin, strong hydrogen bonds from several closely related conformations of the distal histidine (His E 7 ) side chain preferentially stabilize bound oxygen. In Leghemoglobin, the imidazole side chain of His E 7 is confined to a single conformation, which only weakly hydrogen bonds to bound ligands. The phenol side chain of Tyr B 1 0 appears to "fix" the position of His E 7 , probably by donating a hydrogen bond to the Nδ atom of the imidazole side chain. The proximal pocket of Leghemoglobin is designed to favor strong coordination bonds between the heme iron and axial ligands. Thus, high oxygen affinity in Leghemoglobin is established by a favorable staggered geometry of the proximal histidine. The interaction between His E 7 and Tyr B 1 0 prevents overstabilization of bound oxygen. If hydrogen bonding from His E 7 were as strong as it is in mammalian myoglobin, the resultant ultrahigh affinity of Leghemoglobin would prevent oxygen transport in root nodules.
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Distal heme pocket regulation of ligand binding and stability in soybean Leghemoglobin
Proteins, 2003Co-Authors: Suman Kundu, Mark S. HargroveAbstract:Leghemoglobins facilitate diffusion of oxygen through root tissue to a bacterial terminal oxidase in much the same way that myoglobin transports oxygen from blood to muscle cell mitochondria. Leghemoglobin serves an additional role as an oxygen scavenger to prevent inhibition of nitrogen fixation. For this purpose, the oxygen affinity of soybean Leghemoglobin is 20-fold greater than myoglobin, resulting from an 8-fold faster association rate constant combined with a 3-fold slower dissociation rate constant. Although the biochemical mechanism used by myoglobin to bind oxygen has been described in elegant detail, an explanation for the difference in affinity between these two structurally similar proteins is not obvious. The present work demonstrates that, despite their similar structures, Leghemoglobin uses methods different from myoglobin to regulate ligand affinity. Oxygen and carbon monoxide binding to a comprehensive set of Leghemoglobin distal heme pocket mutant proteins in comparison to their myoglobin counterparts has revealed some of these mechanisms. The "distal histidine" provides a crucial hydrogen bond to stabilize oxygen in myoglobin but has little effect on bound oxygen in Leghemoglobin and is retained mainly for reasons of protein stability and prevention of heme loss. Furthermore, soybean Leghemoglobin uses an unusual combination of HisE7 and TyrB10 to sustain a weak stabilizing interaction with bound oxygen. Thus, the Leghemoglobin distal heme pocket provides a much lower barrier to oxygen association than occurs in myoglobin and oxygen dissociation is regulated from the proximal heme pocket.
Michael K. Udvardi - One of the best experts on this subject based on the ideXlab platform.
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Metabolism of reactive oxygen species is attenuated in Leghemoglobin-deficient nodules of Lotus japonicus.
Molecular plant-microbe interactions : MPMI, 2007Co-Authors: Catrin S. Günther, Armin Schlereth, Michael K. Udvardi, Thomas OttAbstract:Leghemoglobins together with high rates of respiration are believed to be major sources of reactive oxygen species (ROS) in root nodules of leguminous plants. High capacities of antioxidative systems apparently protect this organ from oxidative damage. Using Leghemoglobin-RNA interference (LbRNAi) lines of Lotus japonicus, we found that loss of Leghemoglobin results in significantly lower H2O2 levels in nodules. Transcript levels and catalytic activities of ascorbate-glutathione cycle enzymes involved in H2O2 detoxification as well as concentrations of reduced ascorbate were also altered in LbRNAi nodules. Thus, symbiotic Leghemoglobins contribute significantly to ROS generation in functional nodules.
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symbiotic Leghemoglobins are crucial for nitrogen fixation in legume root nodules but not for general plant growth and development
Current Biology, 2005Co-Authors: Thomas Ott, Catrin S. Günther, Joost T Van Dongen, Lene Krusell, Guilhem Desbrosses, Helene Vigeolas, Vivien Bock, Tomasz Czechowski, Peter Geigenberger, Michael K. UdvardiAbstract:Hemoglobins are ubiquitous in nature and among the best-characterized proteins. Genetics has revealed crucial roles for human hemoglobins, but similar data are lacking for plants. Plants contain symbiotic and nonsymbiotic hemoglobins; the former are thought to be important for symbiotic nitrogen fixation (SNF). In legumes, SNF occurs in specialized organs, called nodules, which contain millions of nitrogen-fixing rhizobia, called bacteroids. The induction of nodule-specific plant genes, including those encoding symbiotic Leghemoglobins (Lb), accompanies nodule development. Leghemoglobins accumulate to millimolar concentrations in the cytoplasm of infected plant cells prior to nitrogen fixation and are thought to buffer free oxygen in the nanomolar range, avoiding inactivation of oxygen-labile nitrogenase while maintaining high oxygen flux for respiration. Although widely accepted, this hypothesis has never been tested in planta. Using RNAi, we abolished symbiotic Leghemoglobin synthesis in nodules of the model legume Lotus japonicus. This caused an increase in nodule free oxygen, a decrease in the ATP/ADP ratio, loss of bacterial nitrogenase protein, and absence of SNF. However, LbRNAi plants grew normally when fertilized with mineral nitrogen. These data indicate roles for Leghemoglobins in oxygen transport and buffering and prove for the first time that plant hemoglobins are crucial for symbiotic nitrogen fixation.
Cyril A. Appleby - One of the best experts on this subject based on the ideXlab platform.
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Nicotinate, Nicotinamide, and the Reactivity of Leghemoglobin in Soybean Root Nodules
Plant Physiology, 1991Co-Authors: Robert V. Klucas, Cyril A. ApplebyAbstract:Nicotinate has been postulated to interfere with the binding of O2 to ferrous Leghemoglobin in soybean (Glycine max) root nodules. For such a function, the levels of nicotinate in nodules must be sufficiently high to bind a significant amount of Leghemoglobin. We have measured levels of nicotinate, nicotinamide, and Leghemoglobin in soybean nodules from plants 34 to 73 days after planting in a glasshouse. On a per gram nodule fresh weight basis, levels between 10.4 and 21 nanomoles for nicotinate, 19.2 and 37.8 nanomoles for nicotinamide, and 170 to 280 nanomoles for Leghemoglobin were measured. Even if all the nicotinate were bound to ferrous Leghemoglobin, only 11% or less of the total Leghemoglobin would be unavailable for binding O2. Using the measured levels of nicotinate and a pH of 6.8 in the cytosol of presenescent soybean nodules, we estimate that the proportion of ferrous Leghemoglobin bound to nicotinate in such nodules would be less than 1%. These levels of nicotinate are too low to interfere with the reaction between ferrous Leghemoglobin and O2 in soybean root nodules.