Role of Reversible Histidine Coordination in Hydroxylamine Reduction by Plant Hemoglobins (Phytoglobins)

Athwal, Navjot Singh; Alagurajan, Jagannathan; Andreotti, Amy H.; Hargrove, Mark S.

doi:10.1021/acs.biochem.6b00775

Cited by 10 publications

(32 citation statements)

References 50 publications

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“…However, plant and cyanobacterial Hbs catalyze the reduction of hydroxylamine to ammonium at rates 100–2500 times faster than animal globins, including Ngb. These results support the view that plant and cyanobacterial hemoglobins contribute to anaerobic nitrogen metabolism in support of anaerobic respiration and survival during hypoxia [ 122 , 123 , 124 ]. Under anaerobic conditions, human Ngb(II) reduces NH 2 OH to NH 4 + , being converted to Ngb(III).…”

Section: Nh 2 Oh Reduction By Ngb(ii)supporting

confidence: 87%

Structural and (Pseudo-)Enzymatic Properties of Neuroglobin: Its Possible Role in Neuroprotection

Sbardella

Oddone

et al. 2021

Cells

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Neuroglobin (Ngb), the third member of the globin family, was discovered in human and murine brains in 2000. This monomeric globin is structurally similar to myoglobin (Mb) and hemoglobin (Hb) α and β subunits, but it hosts a bis-histidyl six-coordinated heme-Fe atom. Therefore, the heme-based reactivity of Ngb is modulated by the dissociation of the distal HisE7-heme-Fe bond, which reflects in turn the redox state of the cell. The high Ngb levels (~100–200 μM) present in the retinal ganglion cell layer and in the optic nerve facilitate the O2 buffer and delivery. In contrast, the very low levels of Ngb (~1 μM) in most tissues and organs support (pseudo-)enzymatic properties including NO/O2 metabolism, peroxynitrite and free radical scavenging, nitrite, hydroxylamine, hydrogen sulfide reduction, and the nitration of aromatic compounds. Here, structural and (pseudo-)enzymatic properties of Ngb, which are at the root of tissue and organ protection, are reviewed, envisaging a possible role in the protection from neuronal degeneration of the retina and the optic nerve.

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Section: Nh 2 Oh Reduction By Ngb(ii)supporting

confidence: 87%

Structural and (Pseudo-)Enzymatic Properties of Neuroglobin: Its Possible Role in Neuroprotection

Sbardella

Oddone

et al. 2021

Cells

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“…Unlike NO 2 − reduction, the reaction with NH 2 OH can be sustained catalytically at a rate limited only by the dissociation of the distal His from the ferrous heme iron. Further, it requires His hexacoordination for rapid reduction (Athwal et al , ; Alagurajan et al , ).…”

Section: Globins Of Angiospermsmentioning

confidence: 99%

Plant hemoglobins: a journey from unicellular green algae to vascular plants

et al. 2020

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Globins (Glbs) are widely distributed in archaea, bacteria and eukaryotes. They can be classified into proteins with 2/2 or 3/3 a-helical folding around the heme cavity. Both types of Glbs occur in green algae, bryophytes and vascular plants. The Glbs of angiosperms have been more intensively studied, and several protein structures have been solved. They can be hexacoordinate or pentacoordinate, depending on whether a histidine is coordinating or not at the sixth position of the iron atom. The 3/3 Glbs of class 1 and the 2/2 Glbs (also called class 3 in plants) are present in all angiosperms, whereas the 3/3 Glbs of class 2 have been only found in early angiosperms and eudicots. The three Glb classes are expected to play different roles. Class 1 Glbs are involved in hypoxia responses and modulate NO concentration, which may explain their roles in plant morphogenesis, hormone signaling, cell fate determination, nutrient deficiency, nitrogen metabolism and plant-microorganism symbioses. Symbiotic Glbs derive from class 1 or class 2 Glbs and transport O 2 in nodules. The physiological roles of class 2 and class 3 Glbs are poorly defined but could involve O 2 and NO transport and/or metabolism, respectively. More research is warranted on these intriguing proteins to determine their non-redundant functions.

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“…Redox reactions between ferrous Hb (Hb 2+ ) and nitric oxide, nitrite, and hydroxylamine (HA) are important in anaerobic biology. ,− The reaction of Hb 2+ with nitrite yields ferric Hb (Hb 3+ ) and nitric oxide, which rapidly binds unreacted Hb 2+ and inhibits subsequent reactions. , For this reason, examinations of nitrite reduction by Hbs have been limited to single-turnover reactions. Hb-catalyzed reduction of HA produces ammonium, which does not inhibit further reactions.…”

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confidence: 99%

Steady-State Kinetics of Phytoglobin-Catalyzed Reduction of Hydroxylamine to Ammonium

2018

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Phytoglobins are plant hexacoordinate hemoglobins with reversible coordination of a histidine side chain to the ligand binding site of the heme iron. They mediate electron transfer reactions such as nitric oxide scavenging and are particularly efficient at reducing nitrite and hydroxylamine. Previous work with phytoglobins has focused only on single turnovers of these reactions and has not revealed whether structural features, such as histidine hexacoordination, play a prominent role in the complete catalytic cycle. This work characterizes steady-state phytoglobin catalysis of reduction of hydroxylamine to ammonium using two different chemical reductants. K and k values were measured for rice phytoglobin, horse myoglobin, human neuroglobin, and a rice phytoglobin mutant protein in which the hexacoordinating histidine has been replaced with leucine (Phyt:H73L). The results demonstrate that phytoglobin catalysis driven by benzyl viologen is limited only by the dissociation rate constant for the distal histidine. This is consistent with the rate limit in single-turnover experiments and demonstrates that the kinetics of hydroxylamine binding, and not phytoglobin reduction, ultimately governs the reaction. Catalysis by the other proteins that either lack or have tighter hexacoordination is much slower, suggesting that facile reversibility of the bond between the distal histidine and the heme iron is needed to allow both substrate binding and heme iron reduction. On the other hand, catalysis driven by dithionite is limited by SO concentrations and is similar for all of these proteins, suggesting that dithionite is not a good reducing agent for evaluation of the catalytic properties of hemoglobins.

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Role of Reversible Histidine Coordination in Hydroxylamine Reduction by Plant Hemoglobins (Phytoglobins)

Cited by 10 publications

References 50 publications

Structural and (Pseudo-)Enzymatic Properties of Neuroglobin: Its Possible Role in Neuroprotection

Structural and (Pseudo-)Enzymatic Properties of Neuroglobin: Its Possible Role in Neuroprotection

Plant hemoglobins: a journey from unicellular green algae to vascular plants

Steady-State Kinetics of Phytoglobin-Catalyzed Reduction of Hydroxylamine to Ammonium

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