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Adepu KK, Anishkin A, Adams SH, Chintapalli SV. A versatile delivery vehicle for cellular oxygen and fuels or metabolic sensor? A review and perspective on the functions of myoglobin. Physiol Rev 2024; 104:1611-1642. [PMID: 38696337 DOI: 10.1152/physrev.00031.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 04/30/2024] [Accepted: 05/01/2024] [Indexed: 05/04/2024] Open
Abstract
A canonical view of the primary physiological function of myoglobin (Mb) is that it is an oxygen (O2) storage protein supporting mitochondrial oxidative phosphorylation, especially as the tissue O2 partial pressure (Po2) drops and Mb off-loads O2. Besides O2 storage/transport, recent findings support functions for Mb in lipid trafficking and sequestration, interacting with cellular glycolytic metabolites such as lactate (LAC) and pyruvate (PYR), and "ectopic" expression in some types of cancer cells and in brown adipose tissue (BAT). Data from Mb knockout (Mb-/-) mice and biochemical models suggest additional metabolic roles for Mb, especially regulation of nitric oxide (NO) pools, modulation of BAT bioenergetics, thermogenesis, and lipid storage phenotypes. From these and other findings in the literature over many decades, Mb's function is not confined to delivering O2 in support of oxidative phosphorylation but may serve as an O2 sensor that modulates intracellular Po2- and NO-responsive molecular signaling pathways. This paradigm reflects a fundamental change in how oxidative metabolism and cell regulation are viewed in Mb-expressing cells such as skeletal muscle, heart, brown adipocytes, and select cancer cells. Here, we review historic and emerging views related to the physiological roles for Mb and present working models illustrating the possible importance of interactions between Mb, gases, and small-molecule metabolites in regulation of cell signaling and bioenergetics.
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Affiliation(s)
- Kiran Kumar Adepu
- Arkansas Children's Nutrition Center and Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States
| | - Andriy Anishkin
- Department of Biology, University of Maryland, College Park, Maryland, United States
| | - Sean H Adams
- Department of Surgery, School of Medicine, University of California Davis, Sacramento, California, United States
- Center for Alimentary and Metabolic Science, School of Medicine, University of California Davis, Sacramento, California, United States
| | - Sree V Chintapalli
- Arkansas Children's Nutrition Center and Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States
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2
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Reeder BJ, Svistunenko DA, Wilson MT. Hell's Gate Globin-I from Methylacidiphilum infernorum Displays a Unique Temperature-Independent pH Sensing Mechanism Utililized a Lipid-Induced Conformational Change. Int J Mol Sci 2024; 25:6794. [PMID: 38928500 PMCID: PMC11203436 DOI: 10.3390/ijms25126794] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Revised: 06/05/2024] [Accepted: 06/14/2024] [Indexed: 06/28/2024] Open
Abstract
Hell's Gate globin-I (HGb-I) is a thermally stable globin from the aerobic methanotroph Methylacidiphilium infernorum. Here we report that HGb-I interacts with lipids stoichiometrically to induce structural changes in the heme pocket, changing the heme iron distal ligation coordination from hexacoordinate to pentacoordinate. Such changes in heme geometry have only been previously reported for cytochrome c and cytoglobin, linked to apoptosis regulation and enhanced lipid peroxidation activity, respectively. However, unlike cytoglobin and cytochrome c, the heme iron of HGb-I is altered by lipids in ferrous as well as ferric oxidation states. The apparent affinity for lipids in this thermally stable globin is highly pH-dependent but essentially temperature-independent within the range of 20-60 °C. We propose a mechanism to explain these observations, in which lipid binding and stability of the distal endogenous ligand are juxtaposed as a function of temperature. Additionally, we propose that these coupled equilibria may constitute a mechanism through which this acidophilic thermophile senses the pH of its environment.
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Affiliation(s)
- Brandon J. Reeder
- School of Biological Sciences, University of Essex, Wivenhoe Park Colchester, Essex CO4 3SQ, UK; (D.A.S.); (M.T.W.)
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3
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Ben Brahim N, Touaiti S, Sellés J, Lambry JC, Negrerie M. The control of nitric oxide dynamics and interaction with substituted zinc-phthalocyanines. Dalton Trans 2024; 53:772-780. [PMID: 38086651 DOI: 10.1039/d3dt03356b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2024]
Abstract
Phthalocyanines are artificial macrocycles that can harbour a central metal atom with four symmetric coordinations. Similar to metal-porphyrins, metal-phthalocyanines (M-PCs) may bind small molecules, especially diatomic gases such as NO and O2. Furthermore, various chemical chains can be grafted at the periphery of the M-PC macrocycle, which can change its properties, including the interaction with diatomic gases. In this study, we synthesized Zn-PCs with two different substituents and investigated their effects on the interaction and dynamics of nitric oxide (NO). Time-resolved absorption spectroscopy from picosecond to millisecond revealed that NO dynamics dramatically depends on the nature of the groups grafted to the Zn-PC macrocycle. These experimental results were rationalized by DFT calculations, which demonstrate that electrostatic interactions between NO and the quinoleinoxy substituent modify the potential energy surface and decrease the energy barrier for NO recombination, thus controlling its affinity.
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Affiliation(s)
- Nassim Ben Brahim
- Laboratoire des Interfaces et Matériaux Avancés, Faculté des Sciences de Monastir, Bd. de l'Environnement, 5019 Monastir, Tunisia
| | - Sarra Touaiti
- Laboratoire de Chimie Organique et Analytique, Institut Supérieur de l'Education et de la Formation Continue, 2000 Bardo, Tunisia
| | - Julien Sellés
- Laboratoire de Biologie du Chloroplaste et Perception de la Lumière chez les Micro-Algues, UMR 7141 CNRS-Sorbonne Université, Institut de Biologie Physico-Chimique, 75005 Paris, France
| | - Jean-Christophe Lambry
- Laboratoire d'Optique et Biosciences, INSERM U-1182, CNRS UMR-7645, Ecole Polytechnique, Palaiseau, France.
| | - Michel Negrerie
- Laboratoire d'Optique et Biosciences, INSERM U-1182, CNRS UMR-7645, Ecole Polytechnique, Palaiseau, France.
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4
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Williams MD, Ragireddy V, Dent MR, Tejero J. Engineering neuroglobin nitrite reductase activity based on myoglobin models. Biochem Biophys Rep 2023; 36:101560. [PMID: 37929291 PMCID: PMC10623171 DOI: 10.1016/j.bbrep.2023.101560] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 10/13/2023] [Indexed: 11/07/2023] Open
Abstract
Neuroglobin is a hemoprotein expressed in several nervous system cell lineages with yet unknown physiological functions. Neuroglobin presents a very similar structure to that of the related globins hemoglobin and myoglobin, but shows an hexacoordinate heme as compared to the pentacoordinated heme of myoglobin and hemoglobin. While several reactions of neuroglobin have been characterized in vitro, the relative importance of most of those reactions in vivo is yet undefined. Neuroglobin, like other heme proteins, can reduce nitrite to nitric oxide, providing a possible route to generate nitric oxide in vivo in low oxygen conditions. The reaction kinetics are highly dependent on the nature of the distal residue, and replacement of the distal histidine His64(E7) can increase the reaction rate constants by several orders of magnitude. However, mutation of other distal pocket positions such as Phe28(B10) or Val68(E11) has more limited impact on the rates. Computational analysis using myoglobin as template, guided by the structure of dedicated nitrite reductases like cytochrome cd1 nitrite reductase, has pointed out that combined mutations of the residues B10 and CD1 could increase the nitrite reductase activity of myoglobin, by mimicking the environment of the distal heme pocket in cytochrome cd1 nitrite reductase. As neuroglobin shows high sequence and structural homology with myoglobin, we hypothesized that such mutations (F28H and F42Y in neuroglobin) could also modify the nitrite reductase activity of neuroglobin. Here we study the effect of these mutations. Unfortunately, we do not observe in any case an increase in the nitrite reduction rates. Our results provide some further indications of nitrite reductase regulation in neuroglobin and highlight the minor but critical differences between the structure of penta- and hexacoordinate globins.
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Affiliation(s)
- Mark D. Williams
- Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, 15261, USA
| | - Venkata Ragireddy
- Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, 15261, USA
| | - Matthew R. Dent
- Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, 15261, USA
| | - Jesús Tejero
- Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, 15261, USA
- Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, 15261, USA
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, 15260, USA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, 15261, USA
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Wu G, Sharina I, Martin E. Soluble guanylyl cyclase: Molecular basis for ligand selectivity and action in vitro and in vivo. Front Mol Biosci 2022; 9:1007768. [PMID: 36304925 PMCID: PMC9592903 DOI: 10.3389/fmolb.2022.1007768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2022] [Accepted: 09/27/2022] [Indexed: 01/14/2023] Open
Abstract
Nitric oxide (NO), carbon monoxide (CO), oxygen (O2), hydrogen sulfide (H2S) are gaseous molecules that play important roles in the physiology and pathophysiology of eukaryotes. Tissue concentrations of these physiologically relevant gases vary remarkable from nM range for NO to high μM range of O2. Various hemoproteins play a significant role in sensing and transducing cellular signals encoded by gaseous molecules or in transporting them. Soluble guanylyl cyclase (sGC) is a hemoprotein that plays vital roles in a wide range of physiological functions and combines the functions of gaseous sensor and signal transducer. sGC uniquely evolved to sense low non-toxic levels of NO and respond to elevated NO levels by increasing its catalytic ability to generate the secondary signaling messenger cyclic guanosine monophosphate (cGMP). This review discusses sGC's gaseous ligand selectivity and the molecular basis for sGC function as high-affinity and selectivity NO receptor. The effects of other gaseous molecules and small molecules of cellular origin on sGC's function are also discussed.
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Affiliation(s)
- Gang Wu
- Hematology-Oncology Division, Department of Internal Medicine, The University of Texas—McGovern Medical School, Houston, TX, United States,*Correspondence: Gang Wu, ; Emil Martin,
| | - Iraida Sharina
- Cardiology Division, Department of Internal Medicine, The University of Texas—McGovern Medical School, Houston, TX, United States
| | - Emil Martin
- Cardiology Division, Department of Internal Medicine, The University of Texas—McGovern Medical School, Houston, TX, United States,*Correspondence: Gang Wu, ; Emil Martin,
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Ukeri J, Wilson MT, Reeder BJ. Modulating Nitric Oxide Dioxygenase and Nitrite Reductase of Cytoglobin through Point Mutations. Antioxidants (Basel) 2022; 11:antiox11091816. [PMID: 36139890 PMCID: PMC9495915 DOI: 10.3390/antiox11091816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Revised: 09/02/2022] [Accepted: 09/09/2022] [Indexed: 11/16/2022] Open
Abstract
Cytoglobin is a hexacoordinate hemoglobin with physiological roles that are not clearly understood. Previously proposed physiological functions include nitric oxide regulation, oxygen sensing, or/and protection against oxidative stress under hypoxic/ischemic conditions. Like many globins, cytoglobin rapidly consumes nitric oxide under normoxic conditions. Under hypoxia, cytoglobin generates nitric oxide, which is strongly modulated by the oxidation state of the cysteines. This gives a plausible role for this biochemistry in controlling nitric oxide homeostasis. Mutations to control specific properties of hemoglobin and myoglobin, including nitric oxide binding/scavenging and the nitrite reductase activity of various globins, have been reported. We have mapped these key mutations onto cytoglobin, which represents the E7 distal ligand, B2/E9 disulfide, and B10 heme pocket residues, and examined the nitric oxide binding, nitric oxide dioxygenase activity, and nitrite reductase activity. The Leu46Trp mutation decreases the nitric oxide dioxygenase activity > 10,000-fold over wild type, an effect 1000 times greater than similar mutations with other globins. By understanding how particular mutations can affect specific reactivities, these mutations may be used to target specific cytoglobin activities in cell or animal models to help understand the precise role(s) of cytoglobin under physiological and pathophysiological conditions.
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De Simone G, Sbardella D, Oddone F, Pesce A, Coletta M, Ascenzi P. Structural and (Pseudo-)Enzymatic Properties of Neuroglobin: Its Possible Role in Neuroprotection. Cells 2021; 10:cells10123366. [PMID: 34943874 PMCID: PMC8699588 DOI: 10.3390/cells10123366] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Revised: 11/20/2021] [Accepted: 11/23/2021] [Indexed: 12/17/2022] Open
Abstract
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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Affiliation(s)
- Giovanna De Simone
- Dipartimento di Scienze, Università Roma Tre, Viale Marconi 446, 00146 Roma, Italy;
| | | | | | - Alessandra Pesce
- Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16100 Genova, Italy;
| | - Massimo Coletta
- IRCCS Fondazione Bietti, 00198 Roma, Italy; (D.S.); (F.O.)
- Dipartmento di Scienze Cliniche e Medicina Traslazionale, Università di Roma “Tor Vergata”, Via Montpellier 1, 00133 Roma, Italy
- Correspondence: (M.C.); (P.A.); Tel.: +39-06-72596365 (M.C.); +39-06-57336321 (P.A.)
| | - Paolo Ascenzi
- Dipartimento di Scienze, Università Roma Tre, Viale Marconi 446, 00146 Roma, Italy;
- Accademia Nazionale dei Lincei, Via della Lungara 10, 00165 Roma, Italy
- Unità di Neuroendocrinologia, Metabolismo e Neurofarmacologia, IRCSS Fondazione Santa Lucia, 00179 Roma, Italy
- Correspondence: (M.C.); (P.A.); Tel.: +39-06-72596365 (M.C.); +39-06-57336321 (P.A.)
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8
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Olson JS. Kinetic mechanisms for O 2 binding to myoglobins and hemoglobins. Mol Aspects Med 2021; 84:101024. [PMID: 34544605 DOI: 10.1016/j.mam.2021.101024] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Revised: 09/06/2021] [Accepted: 09/12/2021] [Indexed: 11/29/2022]
Abstract
Antonini and Brunori's 1971 book "Hemoglobin and Myoglobin in Their Reactions with Ligands" was a truly remarkable publication that summarized almost 100 years of research on O2 binding to these globins. Over the ensuing 50 years, ultra-fast laser photolysis techniques, high-resolution and time resolved X-ray crystallography, molecular dynamics simulations, and libraries of recombinant myoglobin (Mb) and hemoglobin (Hb) variants have provided structural interpretations of O2 binding to these proteins. The resultant mechanisms provide quantitative descriptions of the stereochemical factors that govern overall affinity, including proximal and distal steric restrictions that affect iron reactivity and favorable positive electrostatic interactions that preferentially stabilize bound O2. The pathway for O2 uptake and release by Mb and subunits of Hb has been mapped by screening libraries of site-directed mutants in laser photolysis experiments. O2 enters mammalian Mb and the α and β subunits of human HbA through a channel created by upward and outward rotation of the distal His at the E7 helical position, is non-covalently captured in the interior of the distal cavity, and then internally forms a bond with the heme Fe(II) atom. O2 dissociation is governed by disruption of hydrogen bonding interactions with His (E7), breakage of the Fe(II)-O2 bond, and then competition between rebinding and escape through the E7-gate. The structural features that govern the rates of both the individual steps and overall reactions have been determined and provide the framework for: (1) defining the physiological functions of specific globins and their evolution; (2) understanding the clinical features of hemoglobinopathies; and (3) designing safer and more efficient acellular hemoglobin-based oxygen carriers (HBOCs) for transfusion therapy, organ preservation, and other commercially relevant O2 transport and storage processes.
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Affiliation(s)
- John S Olson
- Department of Biosciences, Rice University, Houston, TX, 77005, USA.
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Petrik ID, Davydov R, Kahle M, Sandoval B, Dwaraknath S, Ädelroth P, Hoffman B, Lu Y. An Engineered Glutamate in Biosynthetic Models of Heme-Copper Oxidases Drives Complete Product Selectivity by Tuning the Hydrogen-Bonding Network. Biochemistry 2021; 60:346-355. [PMID: 33464878 PMCID: PMC7888536 DOI: 10.1021/acs.biochem.0c00852] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Efficiently carrying out the oxygen reduction reaction (ORR) is critical for many applications in biology and chemistry, such as bioenergetics and fuel cells, respectively. In biology, this reaction is carried out by large, transmembrane oxidases such as heme-copper oxidases (HCOs) and cytochrome bd oxidases. Common to these oxidases is the presence of a glutamate residue next to the active site, but its precise role in regulating the oxidase activity remains unclear. To gain insight into its role, we herein report that incorporation of glutamate next to a designed heme-copper center in two biosynthetic models of HCOs improves O2 binding affinity, facilitates protonation of reaction intermediates, and eliminates release of reactive oxygen species. High-resolution crystal structures of the models revealed extended, water-mediated hydrogen-bonding networks involving the glutamate. Electron paramagnetic resonance of the cryoreduced oxy-ferrous centers at cryogenic temperature followed by thermal annealing allowed observation of the key hydroperoxo intermediate that can be attributed to the hydrogen-bonding network. By demonstrating these important roles of glutamate in oxygen reduction biochemistry, this work offers deeper insights into its role in native oxidases, which may guide the design of more efficient artificial ORR enzymes or catalysts for applications such as fuel cells.
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Affiliation(s)
- Igor D. Petrik
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Roman Davydov
- The Department of Chemistry, Northwestern University, Evanston, Illinois 60201
| | - Maximilian Kahle
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Braddock Sandoval
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Sudharsan Dwaraknath
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Pia Ädelroth
- Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Brian Hoffman
- The Department of Chemistry, Northwestern University, Evanston, Illinois 60201
| | - Yi Lu
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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A new paradigm for gaseous ligand selectivity of hemoproteins highlighted by soluble guanylate cyclase. J Inorg Biochem 2020; 214:111267. [PMID: 33099233 DOI: 10.1016/j.jinorgbio.2020.111267] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Revised: 09/23/2020] [Accepted: 09/27/2020] [Indexed: 02/06/2023]
Abstract
Nitric oxide (NO), carbon monoxide (CO), and oxygen (O2) are important physiological messengers whose concentrations vary in a remarkable range, [NO] typically from nM to several μM while [O2] reaching to hundreds of μM. One of the machineries evolved in living organisms for gas sensing is sensor hemoproteins whose conformational change upon gas binding triggers downstream response cascades. The recently proposed "sliding scale rule" hypothesis provides a general interpretation for gaseous ligand selectivity of hemoproteins, identifying five factors that govern gaseous ligand selectivity. Hemoproteins have intrinsic selectivity for the three gases due to a neutral proximal histidine ligand while proximal strain of heme and distal steric hindrance indiscriminately adjust the affinity of these three gases for heme. On the other hand, multiple-step NO binding and distal hydrogen bond donor(s) specifically enhance affinity for NO and O2, respectively. The "sliding scale rule" hypothesis provides clear interpretation for dramatic selectivity for NO over O2 in soluble guanylate cyclase (sGC) which is an important example of sensor hemoproteins and plays vital roles in a wide range of physiological functions. The "sliding scale rule" hypothesis has so far been validated by all experimental data and it may guide future designs for heme-based gas sensors.
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Current Challenges in the Development of Acellular Hemoglobin Oxygen Carriers by Protein Engineering. Shock 2020; 52:28-40. [PMID: 29112633 DOI: 10.1097/shk.0000000000001053] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
This article reviews the key biochemical mechanisms that govern O2 transport, NO scavenging, and oxidative degradation of acellular hemoglobin (Hb) and how these ideas have been used to try to develop strategies to engineer safer and more effective hemoglobin-based oxygen carriers (HBOCs). Significant toxicities due to acellular Hb have been observed after the administration of HBOCs or after the lysis of red cells, and include rapid clearance and kidney damage due to dissociation into dimers, haptoglobin binding, and macrophage activation; early O2 release leading to decreased tissue perfusion in capillary beds; interference with endothelial and smooth muscle signaling due to nitric oxide (NO) scavenging; autooxidization of heme iron followed by production of reactive oxygen species; and iron overload symptoms due to hemin loss, globin denaturation, iron accumulation, and further inflammation. Protein engineering can be used to mitigate some of these side effects, but requires an in-depth mechanistic understanding of the biochemical and biophysical features of Hb that regulate quaternary structure, O2 affinity, NO dioxygenation, and resistance to oxidation, hemin loss, and unfolding.
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Rozza AM, Menyhárd DK, Oláh J. Gas Sensing by Bacterial H-NOX Proteins: An MD Study. Molecules 2020; 25:molecules25122882. [PMID: 32585836 PMCID: PMC7356049 DOI: 10.3390/molecules25122882] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Revised: 06/17/2020] [Accepted: 06/17/2020] [Indexed: 01/08/2023] Open
Abstract
Gas sensing is crucial for both prokaryotes and eukaryotes and is primarily performed by heme-based sensors, including H-NOX domains. These systems may provide a new, alternative mode for transporting gaseous molecules in higher organisms, but for the development of such systems, a detailed understanding of the ligand-binding properties is required. Here, we focused on ligand migration within the protein matrix: we performed molecular dynamics simulations on three bacterial (Ka, Ns and Cs) H-NOX proteins and studied the kinetics of CO, NO and O2 diffusion. We compared the response of the protein structure to the presence of ligands, diffusion rate constants, tunnel systems and storage pockets. We found that the rate constant for diffusion decreases in the O2 > NO > CO order in all proteins, and in the Ns > Ks > Cs order if single-gas is considered. Competition between gases seems to seriously influence the residential time of ligands spent in the distal pocket. The channel system is profoundly determined by the overall fold, but the sidechain pattern has a significant role in blocking certain channels by hydrophobic interactions between bulky groups, cation-π interactions or hydrogen bonding triads. The majority of storage pockets are determined by local sidechain composition, although certain functional cavities, such as the distal and proximal pockets are found in all systems. A major guideline for the design of gas transport systems is the need to chemically bind the gas molecule to the protein, possibly joining several proteins with several heme groups together.
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Affiliation(s)
- Ahmed M. Rozza
- Department of Inorganic and Analytical Chemistry, Budapest University of Technology, Budapest Szent Gellért tér 4, H-1111 Budapest, Hungary;
- Department of Biotechnology, Faculty of Agriculture, Al-Azhar University, Cairo 11651, Egypt
| | - Dóra K. Menyhárd
- Laboratory of Structural Chemistry and Biology & MTA-ELTE Protein Modelling Research Group, Institute of Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
- Correspondence: (D.K.M.); (J.O.)
| | - Julianna Oláh
- Department of Inorganic and Analytical Chemistry, Budapest University of Technology, Budapest Szent Gellért tér 4, H-1111 Budapest, Hungary;
- Correspondence: (D.K.M.); (J.O.)
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Olson JS. Lessons Learned from 50 Years of Hemoglobin Research: Unstirred and Cell-Free Layers, Electrostatics, Baseball Gloves, and Molten Globules. Antioxid Redox Signal 2020; 32:228-246. [PMID: 31530172 PMCID: PMC6948003 DOI: 10.1089/ars.2019.7876] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Significance: Over the past 50 years, the mechanisms for O2 storage and transport have been determined quantitatively on distance scales from millimeters to tenths of nanometers and timescales from seconds to picoseconds. Recent Advances: In this review, I have described four key conclusions from work done by my group and our close colleagues. (i) O2 uptake by mammalian red cells is limited by diffusion through unstirred water layers adjacent to the cell surface and across cell-free layers adjacent to vessel walls. (ii) In most vertebrates, hemoglobins (Hbs) and myoglobins (Mbs), the distal histidine at the E7 helical position donates a strong hydrogen bond to bound O2, which selectively enhances O2 affinity, prevents carbon monoxide poisoning, and markedly slows autoxidation. (iii) O2 binding to mammalian Hbs and Mbs occurs by migration of the ligand through a channel created by upward rotation of the His(E7) side chain, capture in the empty space of the distal pocket, and then coordination with the ferroprotoporphyrin IX (heme) iron atom. (iv) The assembly of Mbs and Hbs occurs by formation of molten globule intermediates, in which the N- and C-terminal helices have almost fully formed secondary structures, but the heme pockets are disordered and followed by high-affinity binding of heme. Critical Issues: These conclusions indicate that there are often compromises between O2 transport function, holoprotein stability, and the efficiency of assembly. Future Directions: However, the biochemical mechanisms underlying these conclusions provide the framework for understanding globin evolution in greater detail and for engineering more efficient and stable globins.
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Affiliation(s)
- John S Olson
- BioSciences Department, Rice University, Houston, Texas
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14
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Hashimoto K, Koide T, Okawara T, Shimakoshi H, Hori Y, Shiota Y, Yoshizawa K, Hisaeda Y. Redox behaviour of the β-dihydroporphycene cobalt complex: study on the effect of hydrogenation of the ligand. Dalton Trans 2019; 48:872-881. [PMID: 30417918 DOI: 10.1039/c8dt03743d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The dihydrogenated porphycene cobalt(ii) complex was synthesized and electrochemical experiments were carried out. The one-electron reduction of the complex proceeded at the central metal to afford the Co(i) species; in contrast, for the non-hydrogenated porphycene cobalt(ii) complex, the one-electron reduction gave the ligand reduced radical anion species. The reactivity of the one-electron reduced species with alkyl halides showed clear differences between the complexes. Hydrogenation of the β-position of the porphycene makes it possible to generate a central cobalt reduced species possessing a higher reactivity than the ligand reduced radical anion species.
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Affiliation(s)
- Koichi Hashimoto
- Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, Moto-oka 744, Nishi-ku, Fukuoka-shi, Fukuoka 819-0395, Japan.
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15
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Lacy DC. Applications of the Marcus cross relation to inner sphere reduction of O 2: implications in small-molecule activation. Inorg Chem Front 2019. [DOI: 10.1039/c9qi00828d] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The Marcus cross relation is demonstrated to be applicable to inner sphere electron transfer from iron to molecular oxygen by incorporation of the Fe(iii)–O2to Fe(iii) + superoxide BDFE inKeq. A few case-studies are provided as working examples.
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Affiliation(s)
- David C. Lacy
- Department of Chemistry
- University at Buffalo
- State University of New York
- Buffalo
- USA
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16
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Murali R, Gennis RB. Functional importance of Glutamate-445 and Glutamate-99 in proton-coupled electron transfer during oxygen reduction by cytochrome bd from Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2018; 1859:577-590. [PMID: 29719208 DOI: 10.1016/j.bbabio.2018.04.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Revised: 04/25/2018] [Accepted: 04/26/2018] [Indexed: 12/27/2022]
Abstract
The recent X-ray structure of the cytochrome bd respiratory oxygen reductase showed that two of the three heme components, heme d and heme b595, have glutamic acid as an axial ligand. No other native heme proteins are known to have glutamic acid axial ligands. In this work, site-directed mutagenesis is used to probe the roles of these glutamic acids, E445 and E99 in the E. coli enzyme. It is concluded that neither glutamate is a strong ligand to the heme Fe and they are not the major determinates of heme binding to the protein. Although very important, neither glutamate is absolutely essential for catalytic function. The close interactions between the three hemes in cyt bd result in highly cooperative properties. For example, mutation of E445, which is near heme d, has its greatest effects on the properties of heme b595 and heme b558. It is concluded that 1) O2 binds to the hydrophilic side of heme d and displaces E445; 2) E445 forms a salt bridge with R448 within the O2 binding pocket, and both residues play a role to stabilize oxygenated states of heme d during catalysis; 3) E445 and E99 are each protonated accompanying electron transfer to heme d and heme b595, respectively; 4) All protons used to generate water within the heme d active site come from the cytoplasm and are delivered through a channel that must include internal water molecules to assist proton transfer: [cytoplasm] → E107 → E99 (heme b595) → E445 (heme d) → oxygenated heme d.
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Affiliation(s)
- Ranjani Murali
- Department of Biochemistry, University of Illinois, 600 S. Mathews Street, Urbana, IL 61801, USA
| | - Robert B Gennis
- Department of Biochemistry, University of Illinois, 600 S. Mathews Street, Urbana, IL 61801, USA.
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17
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Preparation and characterization of myoglobin reconstituted with Fe(II) oxaporphyrin: The monoanionic macrocycle provides unique cyanide binding behavior for the ferrous species. Inorganica Chim Acta 2018. [DOI: 10.1016/j.ica.2017.06.054] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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18
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Lábas A, Menyhárd DK, Harvey JN, Oláh J. First Principles Calculation of the Reaction Rates for Ligand Binding to Myoglobin: The Cases of NO and CO. Chemistry 2018; 24:5350-5358. [PMID: 29285802 DOI: 10.1002/chem.201704867] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Indexed: 12/12/2022]
Abstract
Ligand binding by proteins is among the most fundamental processes in nature. Among these processes the binding of small gas molecules, such as O2 , CO and NO to heme proteins has traditionally received vivid interest, which was further boosted by their recently recognized significant role in gas sensing in the body. At the heart of the binding of these ligands to the heme group is the spinforbidden reaction between high-spin iron(II) and the ligand yielding a low-spin adduct. We use computational means to address the complete mechanism of CO and NO binding by myoglobin. Considering that it involves several steps occurring on different time scales, molecular dynamics simulations were performed to address the diffusion of the ligand through the enzyme, and DFT calculations in combination with statistical rate calculation to investigate the spin-forbidden reaction. The calculations yielded rate constants in qualitative agreement with experiments and revealed that the bottleneck of NO and CO binding is different; for NO, diffusion was found to be rate-limiting, whereas for CO, the spin-forbidden step is the slowest.
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Affiliation(s)
- Anikó Lábas
- Department of Inorganic Chemistry, Budapest University of Technology and Economics, H-1111, Budapest, Szent Gellért tér 4., Hungary
| | - Dóra K Menyhárd
- MTA-ELTE Protein Modelling Research Group, H-1117, Budapest, Pázmány Péter st. 1/A, Hungary
| | - Jeremy N Harvey
- Department of Chemistry, KU Leuven, B-3001, Leuven Celestijnenlaan 200F- box 2404, Belgium
| | - Julianna Oláh
- Department of Inorganic Chemistry, Budapest University of Technology and Economics, H-1111, Budapest, Szent Gellért tér 4., Hungary
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19
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Bindings of NO, CO, and O 2 to multifunctional globin type dehaloperoxidase follow the 'sliding scale rule'. Biochem J 2017; 474:3485-3498. [PMID: 28899945 DOI: 10.1042/bcj20170515] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Revised: 09/06/2017] [Accepted: 09/12/2017] [Indexed: 01/09/2023]
Abstract
Dehaloperoxidase-hemoglobin (DHP), a multifunctional globin protein, not only functions as an oxygen carrier as typical globins such as myoglobin and hemoglobin, but also as a peroxidase, a mono- and dioxygenase, peroxygenase, and an oxidase. Kinetics of DHP binding to NO, CO, and O2 were characterized for wild-type DHP A and B and the H55D and H55V DHP A mutants using stopped-flow methods. All three gaseous ligands bind to DHP significantly more weakly than sperm whale myoglobin (SWMb). Both CO and NO bind to DHP in a one-step process to form a stable six-coordinate complex. Multiple-step NO binding is not observed in DHP, which is similar to observations in SWMb, but in contrast with many heme sensor proteins. The weak affinity of DHP for O2 is mainly due to a fast O2 dissociation rate, in accordance with a longer εN-Fe distance between the heme iron and distal histidine in DHP than that in Mb, and an open-distal pocket that permits ligand escape. Binding affinities in DHP show the same 3-4 orders separation between the pairs NO/CO and CO/O2, consistent with the 'sliding scale rule' hypothesis. Strong gaseous ligand discrimination by DHP is very different from that observed in typical peroxidases, which show poor gaseous ligand selectivity, correlating with a neutral proximal imidazole ligand rather than an imidazolate. The present study provides useful insights into the rationale for DHP to function both as mono-oxygenase and oxidase, and is the first example of a globin peroxidase shown to follow the 'sliding scale rule' hypothesis in gaseous ligand discrimination.
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20
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21
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Ascenzi P, di Masi A, Leboffe L, Fiocchetti M, Nuzzo MT, Brunori M, Marino M. Neuroglobin: From structure to function in health and disease. Mol Aspects Med 2016; 52:1-48. [DOI: 10.1016/j.mam.2016.10.004] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Revised: 10/27/2016] [Accepted: 10/27/2016] [Indexed: 01/01/2023]
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22
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Andrew CR, Petrova ON, Lamarre I, Lambry JC, Rappaport F, Negrerie M. The Dynamics Behind the Affinity: Controlling Heme-Gas Affinity via Geminate Recombination and Heme Propionate Conformation in the NO Carrier Cytochrome c'. ACS Chem Biol 2016; 11:3191-3201. [PMID: 27709886 DOI: 10.1021/acschembio.6b00599] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nitric oxide (NO) sensors are heme proteins which may also bind CO and O2. Control of heme-gas affinity and their discrimination are achieved by the structural properties and reactivity of the heme and its distal and proximal environments, leading to several energy barriers. In the bacterial NO sensor cytochrome c' from Alcaligenes xylosoxidans (AXCP), the single Leu16Ala distal mutation boosts the affinity for gas ligands by a remarkable 106-108-fold, transforming AXCP from one of the lowest affinity gas binding proteins to one of the highest. Here, we report the dynamics of diatomics after photodissociation from wild type and L16A-AXCP over 12 orders of magnitude in time. For the L16A variant, the picosecond geminate rebinding of both CO and NO appears with an unprecedented 100% yield, and no exit of these ligands from protein to solvent could be observed. Molecular dynamic simulations saliently demonstrate that dissociated CO stays within 4 Å from Fe2+, in contrast to wild-type AXCP. The L16A mutation confers a heme propionate conformation and docking site which traps the diatomics, maximizing the probability of recombination and directly explaining the ultrahigh affinities for CO, NO, and O2. Overall, our results point to a novel mechanism for modulating heme-gas affinities in proteins.
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Affiliation(s)
- Colin R. Andrew
- Department
of Chemistry and Biochemistry, Eastern Oregon University, La Grande, Oregon 97850, United States
| | - Olga N. Petrova
- Laboratoire
d’Optique et Biosciences, INSERM, Ecole Polytechnique, 91128 Palaiseau, France
| | - Isabelle Lamarre
- Laboratoire
d’Optique et Biosciences, INSERM, Ecole Polytechnique, 91128 Palaiseau, France
| | - Jean-Christophe Lambry
- Laboratoire
d’Optique et Biosciences, INSERM, Ecole Polytechnique, 91128 Palaiseau, France
| | - Fabrice Rappaport
- Laboratoire
de Physiologie Membranaire et Moléculaire du Chloroplaste, CNRS, Université Pierre et Marie Curie, 75005 Paris, France
| | - Michel Negrerie
- Laboratoire
d’Optique et Biosciences, INSERM, Ecole Polytechnique, 91128 Palaiseau, France
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23
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Tracking evolution of myoglobin stability in cetaceans using experimentally calibrated computational methods that account for generic protein relaxation. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2016; 1864:825-34. [DOI: 10.1016/j.bbapap.2016.04.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Revised: 04/05/2016] [Accepted: 04/07/2016] [Indexed: 11/22/2022]
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24
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Abstract
If life without heme-Fe were at all possible, it would definitely be different. Indeed this complex and versatile iron-porphyrin macrocycle upon binding to different “globins” yields hemeproteins crucial to sustain a variety of vital functions, generally classified, for convenience, in a limited number of functional families. Over-and-above the array of functions briefly outlined below, the spectacular progress in molecular genetics seen over the last 30 years led to the discovery of many hitherto unknown novel hemeproteins in prokaryotes and eukaryotes. Here, we highlight a few basic aspects of the chemistry of the hemeprotein universe, in particular those that are relevant to the control of heme-Fe reactivity and specialization, as sculpted by a variety of interactions with the protein moiety.
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Affiliation(s)
- Paolo Ascenzi
- Dipartimento di Scienze, Università Roma Tre, Viale Marconi 446, I-00146 Roma, Italy
| | - Maurizio Brunori
- Dipartimento di Scienze Biochimiche “Alessandro Rossi Fanelli” and Istituto Pasteur — Fondazione Cenci, Bolognetti, Sapienza Università di Roma, Piazzale Aldo Moro 5, I-00185 Roma, Italy
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25
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Mukhi N, Dhindwal S, Uppal S, Kapoor A, Arya R, Kumar P, Kaur J, Kundu S. Structural and Functional Significance of the N- and C-Terminal Appendages in Arabidopsis Truncated Hemoglobin. Biochemistry 2016; 55:1724-40. [PMID: 26913482 DOI: 10.1021/acs.biochem.5b01013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Plant hemoglobins constitute three distinct groups: symbiotic, nonsymbiotic, and truncated hemoglobins. Structural investigation of symbiotic and nonsymbiotic (class I) hemoglobins revealed the presence of a vertebrate-like 3/3 globin fold in these proteins. In contrast, plant truncated hemoglobins are similar to bacterial truncated hemoglobins with a putative 2/2 α-helical globin fold. While multiple structures have been reported for plant hemoglobins of the first two categories, for plant truncated globins only one structure has been reported of late. Here, we report yet another crystal structure of the truncated hemoglobin from Arabidopsis thaliana (AHb3) with two water molecules in the heme pocket, of which one is distinctly coordinated to the heme iron, unlike the only available crystal structure of AHb3 with a hydroxyl ligand. AHb3 was monomeric in its crystallographic asymmetric unit; however, dimer was evident in the crystallographic symmetry, and the globin indeed existed as a stable dimer in solution. The tertiary structure of the protein exhibited a bacterial-like 2/2 α-helical globin fold with an additional N-terminal α-helical extension and disordered C-termini. To address the role of these extended termini in AHb3, which is yet unknown, N- and C-terminal deletion mutants were created and characterized and molecular dynamics simulations performed. The C-terminal deletion had an insignificant effect on most properties but perturbed the dimeric equilibrium of AHb3 and significantly influenced azide binding kinetics in the ferric state. These results along with the disordered nature of the C-terminus indicated its putative role in intramolecular or intermolecular interactions probably regulating protein-ligand and protein-protein interactions. While the N-terminal deletion did not change the overall globin fold, stability, or ligand binding kinetics, it seemed to have influenced coordination at the heme iron, the hydration status of the active site, and the quaternary structure of AHb3. Evidence indicated that the N-terminus is the predominant factor regulating the quaternary interaction appropriate to physiological requirements, dynamics of the side chains in the heme pocket, and tunnel organization in the protein matrix.
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Affiliation(s)
- Nitika Mukhi
- Department of Genetics, University of Delhi South Campus , New Delhi 110021, India
| | - Sonali Dhindwal
- Department of Biotechnology, Indian Institute of Technology , Roorkee, Uttarakhand 247667, India
| | - Sheetal Uppal
- Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India
| | - Abhijeet Kapoor
- Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India
| | - Richa Arya
- Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India
| | - Pravindra Kumar
- Department of Biotechnology, Indian Institute of Technology , Roorkee, Uttarakhand 247667, India
| | - Jagreet Kaur
- Department of Genetics, University of Delhi South Campus , New Delhi 110021, India
| | - Suman Kundu
- Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India
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26
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Uppal S, Salhotra S, Mukhi N, Zaidi FK, Seal M, Dey SG, Bhat R, Kundu S. Significantly enhanced heme retention ability of myoglobin engineered to mimic the third covalent linkage by nonaxial histidine to heme (vinyl) in synechocystis hemoglobin. J Biol Chem 2014; 290:1979-93. [PMID: 25451928 DOI: 10.1074/jbc.m114.603225] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Heme proteins, which reversibly bind oxygen and display a particular fold originally identified in myoglobin (Mb), characterize the "hemoglobin (Hb) superfamily." The long known and widely investigated Hb superfamily, however, has been enriched by the discovery and investigation of new classes and members. Truncated Hbs typify such novel classes and exhibit a distinct two-on-two α-helical fold. The truncated Hb from the freshwater cyanobacterium Synechocystis exhibits hexacoordinate heme chemistry and bears an unusual covalent bond between the nonaxial His(117) and a heme porphyrin 2-vinyl atom, which remains tightly associated with the globin unlike any other. It seems to be the most stable Hb known to date, and His(117) is the dominant force holding the heme. Mutations of amino acid residues in the vicinity did not influence this covalent linkage. Introduction of a nonaxial His into sperm whale Mb at the topologically equivalent position and in close proximity to vinyl group significantly increased the heme stability of this prototype globin. Reversed phase chromatography, electrospray ionization-MS, and MALDI-TOF analyses confirmed the presence of covalent linkage in Mb I107H. The Mb mutant with the engineered covalent linkage was stable to denaturants and exhibited ligand binding and auto-oxidation rates similar to the wild type protein. This indeed is a novel finding and provides a new perspective to the evolution of Hbs. The successful attempt at engineering heme stability holds promise for the production of stable Hb-based blood substitute.
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Affiliation(s)
- Sheetal Uppal
- From the Department of Biochemistry, University of Delhi South Campus, New Delhi 110021, India
| | - Shikha Salhotra
- From the Department of Biochemistry, University of Delhi South Campus, New Delhi 110021, India
| | - Nitika Mukhi
- From the Department of Biochemistry, University of Delhi South Campus, New Delhi 110021, India
| | - Fatima Kamal Zaidi
- the School of Biotechnology, Jawaharlal Nehru University, New Delhi 110067, India, and
| | - Manas Seal
- the Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
| | - Somdatta Ghosh Dey
- the Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
| | - Rajiv Bhat
- the School of Biotechnology, Jawaharlal Nehru University, New Delhi 110067, India, and
| | - Suman Kundu
- From the Department of Biochemistry, University of Delhi South Campus, New Delhi 110021, India,
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27
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Wang C, Lovelace LL, Sun S, Dawson JH, Lebioda L. Structures of K42N and K42Y sperm whale myoglobins point to an inhibitory role of distal water in peroxidase activity. ACTA ACUST UNITED AC 2014; 70:2833-9. [DOI: 10.1107/s1399004714017787] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2014] [Accepted: 08/01/2014] [Indexed: 11/10/2022]
Abstract
Sperm whale myoglobin (Mb) functions as an oxygen-storage protein, but in the ferric state it possesses a weak peroxidase activity which enables it to carry out H2O2-dependent dehalogenation reactions. Hemoglobin/dehaloperoxidase fromAmphitrite ornata(DHP) is a dual-function protein represented by two isoproteins DHP A and DHP B; its peroxidase activity is at least ten times stronger than that of Mb and plays a physiological role. The `DHP A-like' K42Y Mb mutant (K42Y) and the `DHP B-like' K42N mutant (K42N) were engineered in sperm whale Mb to mimic the extended heme environments of DHP A and DHP B, respectively. The peroxidase reaction rates increased ∼3.5-fold and ∼5.5-fold in K42Y and K42NversusMb, respectively. The crystal structures of the K42Y and K42N mutants revealed that the substitutions at position 42 slightly elongate not only the distances between the distal His55 and the heme iron but also the hydrogen-bonding distances between His55 and the Fe-coordinated water. The enhanced peroxidase activity of K42Y and K42N thus might be attributed in part to the weaker binding of the axial water molecule that competes with hydrogen peroxide for the binding site at the heme in the ferric state. This is likely to be the mechanism by which the relationship `longer distal histidine to Fe distance – better peroxidase activity', which was previously proposed for heme proteins by Matsuiet al.(1999) (J. Biol. Chem.274, 2838–2844), works. Furthermore, positive cooperativity in K42N was observed when its dehaloperoxidase activity was measured as a function of the concentration of the substrate trichlorophenol. This serendipitously engineered cooperativity was rationalized by K42N dimerization through the formation of a dityrosine bond induced by excess H2O2.
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28
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Sun S, Sono M, Wang C, Du J, Lebioda L, Dawson JH. Influence of heme environment structure on dioxygen affinity for the dual function Amphitrite ornata hemoglobin/dehaloperoxidase. Insights into the evolutional structure-function adaptations. Arch Biochem Biophys 2014; 545:108-15. [PMID: 24440609 DOI: 10.1016/j.abb.2014.01.010] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 01/08/2014] [Accepted: 01/10/2014] [Indexed: 11/28/2022]
Abstract
Sea worm, Amphitrite ornata, has evolved its globin (an O(2) carrier) also to serves as a dehaloperoxidase (DHP) to detoxify haloaromatic pollutants generated by competing species. A previous mutagenesis study by our groups on both DHP and sperm whale myoglobin (SW Mb) revealed some structural factors that influence the dehaloperoxidase activities (significantly lower for Mb) of both proteins. Using an isocyanide/O(2) partition constant measurement method in this study, we have examined the effects of these structural factors on the O(2) equilibrium constants (KO2) of DHP, SW Mb, and their mutants. A clear trend of decreasing O(2) affinity and increasing catalytic activity along with the increase in the distal His N(ε)-heme iron distance is observed. An H93K/T95H Mb double mutant mimicking the DHP proximal His positioning exhibited markedly enhanced O(2) affinity, confirming the essential effect of proximal His rotation on the globin function of DHP. For DHP, the L100F, T56G and M86E variants showed the effects of distal volume, distal His flexibility and proximal electronic push, respectively, on the O(2) affinity. This study provides insights into how DHP has evolved its heme environment to gain significantly enhanced peroxidase capability without compromising its primary function as an O(2) carrier.
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Affiliation(s)
- Shengfang Sun
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States
| | - Masanori Sono
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States.
| | - Chunxue Wang
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States
| | - Jing Du
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States
| | - Lukasz Lebioda
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States.
| | - John H Dawson
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States; School of Medicine, University of South Carolina, United States.
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29
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Ramos-Alvarez C, Yoo BK, Pietri R, Lamarre I, Martin JL, Lopez-Garriga J, Negrerie M. Reactivity and dynamics of H2S, NO, and O2 interacting with hemoglobins from Lucina pectinata. Biochemistry 2013; 52:7007-21. [PMID: 24040745 DOI: 10.1021/bi400745a] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Hemoglobin HbI from the clam Lucina pectinata is involved in H2S transport, whereas homologous heme protein HbII/III is involved in O2 metabolism. Despite similar tertiary structures, HbI and HbII/III exhibit very different reactivity toward heme ligands H2S, O2, and NO. To investigate this reactivity at the heme level, we measured the dynamics of ligand interaction by time-resolved absorption spectroscopy in the picosecond to nanosecond time range. We demonstrated that H2S can be photodissociated from both ferric and ferrous HbI. H2S geminately rebinds to ferric and ferrous out-of-plane iron with time constants (τgem) of 12 and 165 ps, respectively, with very different proportions of photodissociated H2S exiting the protein (24% in ferric and 80% in ferrous HbI). The Gln(E7)His mutation considerably changes H2S dynamics in ferric HbI, indicating the role of Gln(E7) in controling H2S reactivity. In ferric HbI, the rate of diffusion of H2S from the solvent into the heme pocket (kentry) is 0.30 μM(-1) s(-1). For the HbII/III-O2 complex, we observed mainly a six-coordinate vibrationally excited heme-O2 complex with O2 still bound to the iron. This explains the low yield of O2 photodissociation and low koff from HbII/III, compared with those of HbI and Mb. Both isoforms behave very differently with regard to NO and O2 dynamics. Whereas the amplitude of geminate rebinding of O2 to HbI (38.5%) is similar to that of myoglobin (34.5%) in spite of different distal heme sites, it appears to be much larger for HbII/III (77%). The distal Tyr(B10) side chain present in HbII/III increases the energy barrier for ligand escape and participates in the stabilization of bound O2 and NO.
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Affiliation(s)
- Cacimar Ramos-Alvarez
- Department of Chemistry, University of Puerto Rico , Mayagüez Campus, Mayagüez 00680, Puerto Rico
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30
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Liao MS, Huang MJ, Watts JD. Effects of local protein environment on the binding of diatomic molecules to heme in myoglobins. DFT and dispersion-corrected DFT studies. J Mol Model 2013; 19:3307-23. [PMID: 23661270 PMCID: PMC3726265 DOI: 10.1007/s00894-013-1864-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Accepted: 04/18/2013] [Indexed: 10/26/2022]
Abstract
The heme-AB binding energies (AB = CO, O2) in a wild-type myoglobin (Mb) and two mutants (H64L, V68N) of Mb have been investigated in detail with both DFT and dispersion-corrected DFT methods, where H64L and V68N represent two different, opposite situations. Several dispersion correction approaches were tested in the calculations. The effects of the local protein environment were accounted for by including the five nearest surrounding residues in the calculated systems. The specific role of histidine-64 in the distal pocket was examined in more detail in this study than in other studies in the literature. Although the present calculated results do not change the previous conclusion that the hydrogen bonding by the distal histidine-64 residue plays a major role in the O2/CO discrimination by Mb, more details about the interaction between the protein environment and the bound ligand have been revealed in this study by comparing the binding energies of AB to a porphyrin and the various myoglobins. The changes in the experimental binding energies from one system to another are well reproduced by the calculations. Without constraints on the residues in geometry optimization, the dispersion correction is necessary, since it improves the calculated structures and energetic results significantly.
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Affiliation(s)
- Meng-Sheng Liao
- Department of Chemistry, Jackson State University, Jackson, Mississippi 39217, USA
| | - Ming-Ju Huang
- Department of Chemistry, Jackson State University, Jackson, Mississippi 39217, USA
| | - John D. Watts
- Department of Chemistry, Jackson State University, Jackson, Mississippi 39217, USA
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31
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Abstract
SIGNIFICANCE There has been a striking advancement in our understanding of red cell substitutes over the past decade. Although regulatory oversight has influenced many aspects of product development in this period, those who have approached the demonstration of efficacy of red cell substitutes have failed to understand their implication at the level of the microcirculation, where blood interacts closely with tissue. RECENT ADVANCES The understanding of the adverse effects of acellular hemoglobin (Hb)-based oxygen carriers (HBOCs) has fortunately expanded from Hb-induced renal toxicity to a more complete list of biochemical mechanism. In addition, various unexpected adverse reactions were seen in early clinical studies. The effects of the presence of acellular Hb in plasma are relatively unique because of the convergence of mechanical and biochemical natures. CRITICAL ISSUES Controlling the variables using genetic engineering and chemical modification to change specific characteristics of the Hb molecule may allow for solving the complex multivariate problems of acellular Hb vasoactivity. HBOCs may never be rendered free of negative effects; however, quantifying the nature and extent of microvascular complications establishes a platform for designing new ameliorative therapies. FUTURE DIRECTIONS It is time to leave behind the study of vasoactivity and toxicity based on bench-top measurements of biochemical changes and those based solely on systemic parameters in vivo, and move to a more holistic analysis of the mechanisms creating the problems, complemented with meaningful studies of efficacy.
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Affiliation(s)
- Pedro Cabrales
- Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093, USA.
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Abbruzzetti S, Spyrakis F, Bidon-Chanal A, Luque FJ, Viappiani C. Ligand migration through hemeprotein cavities: insights from laser flash photolysis and molecular dynamics simulations. Phys Chem Chem Phys 2013; 15:10686-701. [PMID: 23733145 DOI: 10.1039/c3cp51149a] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The presence of cavities and tunnels in the interior of proteins, in conjunction with the structural plasticity arising from the coupling to the thermal fluctuations of the protein scaffold, has profound consequences on the pathways followed by ligands moving through the protein matrix. In this perspective we discuss how quantitative analysis of experimental rebinding kinetics from laser flash photolysis, trapping of unstable conformational states by embedding proteins within the nanopores of silica gels, and molecular simulations can synergistically converge to gain insight into the migration mechanism of ligands. We show how the evaluation of the free energy landscape for ligand diffusion based on the outcome of computational techniques can assist the definition of sound reaction schemes, leading to a comprehensive understanding of the broad range of chemical events and time scales that encompass the transport of small ligands in hemeproteins.
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Affiliation(s)
- Stefania Abbruzzetti
- Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma, viale delle Scienze 7A, 43124, Parma, Italy
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Tertiary and quaternary effects in the allosteric regulation of animal hemoglobins. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2013; 1834:1860-72. [PMID: 23523886 DOI: 10.1016/j.bbapap.2013.03.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Revised: 03/07/2013] [Accepted: 03/08/2013] [Indexed: 12/16/2022]
Abstract
In the last decade, protein allostery has experienced a major resurgence, boosted by the extension of the concept to systems of increasing complexity and by its exploitation for the development of drugs. Expansion of the field into new directions has not diminished the key role of hemoglobin as a test molecule for theory and experimental validation of allosteric models. Indeed, the diffusion of hemoglobins in all kingdoms of life and the variety of functions and of quaternary assemblies based on a common tertiary fold indicate that this superfamily of proteins is ideally suited for investigating the physical and molecular basis of allostery and firmly maintains its role as a main player in the field. This review is an attempt to briefly recollect common and different strategies adopted by metazoan hemoglobins, from monomeric molecules to giant complexes, exploiting homotropic and heterotropic allostery to increase their functional dynamic range. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.
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Ascenzi P, Marino M, Polticelli F, Coletta M, Gioia M, Marini S, Pesce A, Nardini M, Bolognesi M, Reeder BJ, Wilson MT. Non-covalent and covalent modifications modulate the reactivity of monomeric mammalian globins. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2013; 1834:1750-6. [PMID: 23416443 DOI: 10.1016/j.bbapap.2013.02.012] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Revised: 02/04/2013] [Accepted: 02/07/2013] [Indexed: 01/07/2023]
Abstract
Multimeric globins (e.g., hemoglobin) are considered to be the prototypes of allosteric enzymes, whereas monomeric globins (e.g., myoglobin; Mb) usually are assumed to be non-allosteric. However, the modulation of the functional properties of monomeric globins by non-covalent (or allosteric) and covalent modifications casts doubts on this general assumption. Here, we report examples referable to these two extreme mechanisms modulating the reactivity of three mammalian monomeric globins. Sperm whale Mb, which acts as a reserve supply of O2 and facilitates the O2 flux within a myocyte, displays the allosteric modulation of the O2 affinity on lactate, an obligatory product of glycolysis under anaerobic conditions, thus facilitating O2 diffusion to the mitochondria in supporting oxidative phosphorylation. Human neuroglobin (NGB), which appears to protect neurons from hypoxia in vitro and in vivo, undergoes hypoxia-dependent phosphorylation (i.e., covalent modulation) affecting the coordination equilibrium of the heme-Fe atom and, in turn, the heme-protein reactivity. This facilitates heme-Fe-ligand binding and enhances the rate of anaerobic nitrite reduction to form NO, thus contributing to cellular adaptation to hypoxia. The reactivity of human cytoglobin (CYGB), which has been postulated to protect cells against oxidative stress, depends on both non-covalent and covalent mechanisms. In fact, the heme reactivity of CYGB depends on the lipid, such as oleate, binding which stabilizes the penta-coordination geometry of the heme-Fe atom. Lastly, the reactivity of NGB and CYGB is modulated by the redox state of the intramolecular CysCD7/CysD5 and CysB2/CysE9 residue pairs, respectively, affecting the heme-Fe atom coordination state. In conclusion, the modulation of monomeric globins reactivity by non-covalent and covalent modifications appears a very widespread phenomenon, opening new perspectives in cell survival and protection. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.
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Affiliation(s)
- Paolo Ascenzi
- Interdepartmental Laboratory of Electron Microscopy, University Roma Tre, Roma, Italy.
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Pond MP, Wenke BB, Preimesberger MR, Rice SL, Lecomte JTJ. 3-Fluorotyrosine as a complementary probe of hemoglobin structure and dynamics: a (19)F-NMR study of Synechococcus sp. PCC 7002 GlbN. Chem Biodivers 2013; 9:1703-17. [PMID: 22976963 DOI: 10.1002/cbdv.201100448] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The hemoglobin from the cyanobacterium Synechococcus sp. PCC 7002 (GlbN) contains three tyrosines (Tyr5, Tyr22, and Tyr53), each of which undergoes a structural rearrangement when the protein binds an exogenous ligand such as cyanide. We explored the use of 3-fluorotyrosine and (19)F-NMR spectroscopy for the characterization of GlbN. Assignment of (19)F resonances in fluorinated GlbN (GlbN*) was achieved with individual Tyr5Phe and Tyr53Phe replacements. We observed marked variations in chemical shift and linewidth reflecting the dependence of structural and dynamic properties on oxidation state, ligation state, and covalent attachment of the heme group. The isoelectronic complexes of ferric GlbN* with cyanide and ferrous GlbN* with carbon monoxide gave contrasting spectra, the latter exhibiting heterogeneity and enhanced internal motions on a microsecond-to-millisecond time scale. The strength of the H-bond network involving Tyr22 (B10) and bound cyanide was tested at high pH. 3-Fluorotyrosine at position 22 had a pK(a) value at least 3 units higher than its intrinsic value, 8.5. In addition, evidence was found for long-range communication among the tyrosine sites. These observations demonstrated the utility of the 3-fluorotyrosine approach to gain insight in hemoglobin properties.
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Affiliation(s)
- Matthew P Pond
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA
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Tsai AL, Martin E, Berka V, Olson JS. How do heme-protein sensors exclude oxygen? Lessons learned from cytochrome c', Nostoc puntiforme heme nitric oxide/oxygen-binding domain, and soluble guanylyl cyclase. Antioxid Redox Signal 2012; 17:1246-63. [PMID: 22356101 PMCID: PMC3430480 DOI: 10.1089/ars.2012.4564] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
SIGNIFICANCE Ligand selectivity for dioxygen (O(2)), carbon monoxide (CO), and nitric oxide (NO) is critical for signal transduction and is tailored specifically for each heme-protein sensor. Key NO sensors, such as soluble guanylyl cyclase (sGC), specifically recognized low levels of NO and achieve a total O(2) exclusion. Several mechanisms have been proposed to explain the O(2) insensitivity, including lack of a hydrogen bond donor and negative electrostatic fields to selectively destabilize bound O(2), distal steric hindrance of all bound ligands to the heme iron, and restriction of in-plane movements of the iron atom. RECENT ADVANCES Crystallographic structures of the gas sensors, Thermoanaerobacter tengcongensis heme-nitric oxide/oxygen-binding domain (Tt H-NOX(1)) or Nostoc puntiforme (Ns) H-NOX, and measurements of O(2) binding to site-specific mutants of Tt H-NOX and the truncated β subunit of sGC suggest the need for a H-bonding donor to facilitate O(2) binding. CRITICAL ISSUES However, the O(2) insensitivity of full length sGC with a site-specific replacement of isoleucine by a tyrosine on residue 145 and the very slow autooxidation of Ns H-NOX and cytochrome c' suggest that more complex mechanisms have evolved to exclude O(2) but retain high affinity NO binding. A combined graphical analysis of ligand binding data for libraries of heme sensors, globins, and model heme shows that the NO sensors dramatically inhibit the formation of six-coordinated NO, CO, and O(2) complexes by direct distal steric hindrance (cyt c'), proximal constraints of in-plane iron movement (sGC), or combinations of both following a sliding scale rule. High affinity NO binding in H-NOX proteins is achieved by multiple NO binding steps that produce a high affinity five-coordinate NO complex, a mechanism that also prevents NO dioxygenation. FUTURE DIRECTIONS Knowledge advanced by further extensive test of this "sliding scale rule" hypothesis should be valuable in guiding novel designs for heme based sensors.
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Affiliation(s)
- Ah-Lim Tsai
- Division of Hematology, University of Texas Health Science Center at Houston, Houston, Texas 77225, USA.
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Zapata AL, Kumar MR, Pervitsky D, Farmer PJ. A singular value decomposition approach for kinetic analysis of reactions of HNO with myoglobin. J Inorg Biochem 2012; 118:171-8. [PMID: 23140900 DOI: 10.1016/j.jinorgbio.2012.10.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2012] [Revised: 10/03/2012] [Accepted: 10/04/2012] [Indexed: 12/01/2022]
Abstract
The reactions of several horse heart myoglobin species with nitrosyl hydride, HNO, derived from Angeli's salt (AS) and Piloty's acid (PA) have been followed by UV-visible, (1)H NMR and EPR spectroscopies. Spectral analysis of myoglobin-derived speciation during the reactions was obtained by using singular value decomposition methods combined with a global analysis to obtain the rate constants of complex sequential reactions. The analysis also provided spectra for the derived absorbers, which allowed self-consistent calibration to the spectra of known myoglobin species. Using this method, the determined rate for trapping of HNO by metmyoglobin, which produces NO-myoglobin, is found to be 2.7 × 10(5)M(-1)s(-1) at pH7.0 and 1.1 × 10(5)M(-1)s(-1) at pH9.4. The reaction of deoxymyoglobin with HNO generates the adduct HNO-myoglobin directly, but is followed by a secondary reaction of that product with HNO yielding NO-myoglobin; the determined bimolecular rate constants for these reactions are 3.7 × 10(5)M(-1)s(-1) and 1.67 × 10(4)M(-1)s(-1) respectively, and are independent of pH. The derived spectrum for HNO-myoglobin is characterized by a Soret absorbance maximum at 423 nm with an extinction coefficient of 1.66 × 10(5)M(-1)cm(-1). The rate constant for unimolecular loss of HNO from HNO-myoglobin was determined by competitive trapping with CO at 8.9 × 10(-5)s(-1), which gives the thermodynamic binding affinity of HNO to deoxymyoglobin as 4.2 × 10(9)M(-1). These results suggest that the formation of HNO-ferrous heme protein adducts represents an important consideration in the biological action of HNO-releasing drugs.
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Affiliation(s)
- Adrian L Zapata
- Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76796, USA
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High resolution crystal structures of the Cerebratulus lacteus mini-Hb in the unligated and carbomonoxy states. Int J Mol Sci 2012; 13:8025-8037. [PMID: 22942687 PMCID: PMC3430218 DOI: 10.3390/ijms13078025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Revised: 06/14/2012] [Accepted: 06/15/2012] [Indexed: 11/23/2022] Open
Abstract
The nerve tissue mini-hemoglobin from Cerebratulus lacteus (CerHb) displays an essential globin fold hosting a protein matrix tunnel held to allow traffic of small ligands to and from the heme. CerHb heme pocket hosts the distal TyrB10/GlnE7 pair, normally linked to low rates of O2 dissociation and ultra-high O2 affinity. However, CerHb affinity for O2 is similar to that of mammalian myoglobins, due to a dynamic equilibrium between high and low affinity states driven by the ability of ThrE11 to orient the TyrB10 OH group relative to the heme ligand. We present here the high resolution crystal structures of CerHb in the unligated and carbomonoxy states. Although CO binds to the heme with an orientation different from the O2 ligand, the overall binding schemes for CO and O2 are essentially the same, both ligands being stabilized through a network of hydrogen bonds based on TyrB10, GlnE7, and ThrE11. No dramatic protein structural changes are needed to support binding of the ligands, which can freely reach the heme distal site through the apolar tunnel. A lack of main conformational changes between the heme-unligated and -ligated states grants stability to the folded mini-Hb and is a prerequisite for fast ligand diffusion to/from the heme.
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Human serum albumin: from bench to bedside. Mol Aspects Med 2011; 33:209-90. [PMID: 22230555 DOI: 10.1016/j.mam.2011.12.002] [Citation(s) in RCA: 1195] [Impact Index Per Article: 91.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Accepted: 12/21/2011] [Indexed: 02/07/2023]
Abstract
Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule, representing the main determinant of plasma oncotic pressure and the main modulator of fluid distribution between body compartments. HSA displays an extraordinary ligand binding capacity, providing a depot and carrier for many endogenous and exogenous compounds. Indeed, HSA represents the main carrier for fatty acids, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays (pseudo-)enzymatic properties. HSA is a valuable biomarker of many diseases, including cancer, rheumatoid arthritis, ischemia, post-menopausal obesity, severe acute graft-versus-host disease, and diseases that need monitoring of the glycemic control. Moreover, HSA is widely used clinically to treat several diseases, including hypovolemia, shock, burns, surgical blood loss, trauma, hemorrhage, cardiopulmonary bypass, acute respiratory distress syndrome, hemodialysis, acute liver failure, chronic liver disease, nutrition support, resuscitation, and hypoalbuminemia. Recently, biotechnological applications of HSA, including implantable biomaterials, surgical adhesives and sealants, biochromatography, ligand trapping, and fusion proteins, have been reported. Here, genetic, biochemical, biomedical, and biotechnological aspects of HSA are reviewed.
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Tsai AL, Berka V, Martin E, Olson JS. A "sliding scale rule" for selectivity among NO, CO, and O₂ by heme protein sensors. Biochemistry 2011; 51:172-86. [PMID: 22111978 DOI: 10.1021/bi2015629] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Selectivity among NO, CO, and O₂ is crucial for the physiological function of most heme proteins. Although there is a million-fold variation in equilibrium dissociation constants (K(D)), the ratios for NO:CO:O₂ binding stay roughly the same, 1:~10(3):~10(6), when the proximal ligand is a histidine and the distal site is apolar. For these proteins, there is a "sliding scale rule" for plots of log(K(D)) versus ligand type that allows predictions of K(D) values if one or two are missing. The predicted K(D) for binding of O₂to Ns H-NOX coincides with the value determined experimentally at high pressures. Active site hydrogen bond donors break the rule and selectively increase O₂ affinity with little effect on CO and NO binding. Strong field proximal ligands such as thiolate, tyrosinate, and imidazolate exert a "leveling" effect on ligand binding affinity. The reported picomolar K(D) for binding of NO to sGC deviates even more dramatically from the sliding scale rule, showing a NO:CO K(D) ratio of 1:~10(8). This deviation is explained by a complex, multistep process, in which an initial low-affinity hexacoordinate NO complex with a measured K(D) of ≈54 nM, matching that predicted from the sliding scale rule, is formed initially and then is converted to a high-affinity pentacoordinate complex. This multistep six-coordinate to five-coordinate mechanism appears to be common to all NO sensors that exclude O₂ binding to capture a lower level of cellular NO and prevent its consumption by dioxygenation.
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Affiliation(s)
- Ah-Lim Tsai
- Division of Hematology, Internal Medicine, University of Texas Medical School at Houston, Houston, Texas 77030, United States.
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Yum S, Choi J, Hong S, Park MH, Lee J, Ha NC, Jung Y. Hyperoxia attenuates the inhibitory effect of nitric oxide donors on HIF prolyl-4-hydroxylase-2: Implication on discriminative effect of nitric oxide on HIF prolyl-4-hydroxylase-2 and collagen prolyl-4-hydroxylase. Biochem Pharmacol 2011; 82:485-90. [PMID: 21723853 DOI: 10.1016/j.bcp.2011.05.033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2011] [Revised: 04/28/2011] [Accepted: 05/06/2011] [Indexed: 11/15/2022]
Abstract
Prolyl 4-hydroxylases (P4Hs), such as collagen prolyl-4-hydroxylases (CPHs) and hypoxia inducible factor prolyl-4-hydroxylases (HPHs), have recently been recognized as promising drug targets for the treatment of fibrotic and ischemic diseases. CPHs and HPHs catalyze identical metabolic reactions, yet lead to quite different physiological consequences, collagen synthesis and the regulation of oxygen homeostasis. Selective modulation of the two enzymes should provide a therapeutic benefit upon pharmacotherapy. In an in vitro VHL capture assay, hydroxylation of the 19mer HIF peptide (corresponding to HIF-1α residues 556-574) by HPH-2 was effectively prevented by nitric oxide (NO) donors, (±)-S-nitroso-N-acetylpenicillamine (SNAP) and S-nitrosoglutathione. The NO donors also caused inhibition of HPHs and accumulation of nonhydroxylated HIF-1α protein in A549 human lung adenocarcinoma cells. Hyperoxia (100% O(2)) attenuated both NO donor-induced accumulation of HIF-1α and inhibition of HPH-mediated hydroxylation. In the presence of a proteasome inhibitor, MG132, the hyperoxia-mediated degradation of HIF-1α was deterred and hydroxylated HIF-1α was detected. SNAP, while being an effective inhibitor of proline 4-hydroxylation of HIF-1α by HPH-2, did not diminish proline hydroxylation of collagen by CPHs. Our data suggest that NO inhibits HPH-2 via competing with dioxygen and that the discriminative effect of NO on CPHs and HPH-2 is attributable to the difference in the affinity of the two enzymes toward dioxygen.
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Affiliation(s)
- Soohwan Yum
- College of Pharmacy, Pusan National University, Busan, Republic of Korea
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Birukou I, Maillett DH, Birukova A, Olson JS. Modulating distal cavities in the α and β subunits of human HbA reveals the primary ligand migration pathway. Biochemistry 2011; 50:7361-74. [PMID: 21793487 DOI: 10.1021/bi200923k] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The free volume in the active site of human HbA plays a crucial role in governing the bimolecular rates of O(2), CO, and NO binding, the fraction of geminate ligand recombination, and the rate of NO dioxygenation by the oxygenated complex. We have decreased the size of the distal pocket by mutating Leu(B10), Val(E11), and Leu(G8) to Phe and Trp and that of other more internal cavities by filling them with Xe at high gas pressures. Increasing the size of the B10 side chain reduces bimolecular rates of ligand binding nearly 5000-fold and inhibits CO geminate recombination due to both reduction of the capture volume in the distal pocket and direct steric hindrance of Fe-ligand bond formation. Phe and Trp(E11) mutations also cause a decrease in distal pocket volume but, at the same time, increase access to the Fe atom because of the loss of the γ2 CH(3) group of the native Val(E11) side chain. The net result of these E11 substitutions is a dramatic increase in the rate of geminate recombination because dissociated CO is sequestered close to the Fe atom and can rapidly rebind without steric resistance. However, the bimolecular rate constants for binding of ligand to the Phe and Trp(E11) mutants are decreased 5-30-fold, because of a smaller capture volume. Geminate and bimolecular kinetic parameters for Phe and Trp(G8) mutants are similar to those for the native HbA subunits because the aromatic rings at this position cause little change in distal pocket volume and because ligands do not move past this position into the globin interior of wild-type HbA subunits. The latter conclusion is verified by the observation that Xe binding to the α and β Hb subunits has little effect on either geminate or bimolecular ligand rebinding. All of these experimental results argue strongly against alternative ligand migration pathways that involve movements through the protein interior in HbA. Instead, ligands appear to enter through the His(E7) gate and are captured directly in the distal cavity.
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Affiliation(s)
- Ivan Birukou
- Department of Biochemistry and Cell Biology and WM Keck Center for Computational Biology, Rice University, Houston, Texas 77005, United States
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43
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Pesce A, Nardini M, Dewilde S, Capece L, Martí MA, Congia S, Salter MD, Blouin GC, Estrin DA, Ascenzi P, Moens L, Bolognesi M, Olson JS. Ligand migration in the apolar tunnel of Cerebratulus lacteus mini-hemoglobin. J Biol Chem 2010; 286:5347-58. [PMID: 21147768 DOI: 10.1074/jbc.m110.169045] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The large apolar tunnel traversing the mini-hemoglobin from Cerebratulus lacteus (CerHb) has been examined by x-ray crystallography, ligand binding kinetics, and molecular dynamic simulations. The addition of 10 atm of xenon causes loss of diffraction in wild-type (wt) CerHbO(2) crystals, but Leu-86(G12)Ala CerHbO(2), which has an increased tunnel volume, stably accommodates two discrete xenon atoms: one adjacent to Leu-86(G12) and another near Ala-55(E18). Molecular dynamics simulations of ligand migration in wt CerHb show a low energy pathway through the apolar tunnel when Leu or Ala, but not Phe or Trp, is present at the 86(G12) position. The addition of 10-15 atm of xenon to solutions of wt CerHbCO and L86A CerHbCO causes 2-3-fold increases in the fraction of geminate ligand recombination, indicating that the bound xenon blocks CO escape. This idea was confirmed by L86F and L86W mutations, which cause even larger increases in the fraction of geminate CO rebinding, 2-5-fold decreases in the bimolecular rate constants for ligand entry, and large increases in the computed energy barriers for ligand movement through the apolar tunnel. Both the addition of xenon to the L86A mutant and oxidation of wt CerHb heme iron cause the appearance of an out Gln-44(E7) conformer, in which the amide side chain points out toward the solvent and appears to lower the barrier for ligand escape through the E7 gate. However, the observed kinetics suggest little entry and escape (≤ 25%) through the E7 pathway, presumably because the in Gln-44(E7) conformer is thermodynamically favored.
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Affiliation(s)
- Alessandra Pesce
- Department of Physics, University of Genova, Via Dodecaneso 33, 16146 Genova, Italy
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Ramos C, Pietri R, Lorenzo W, Roman E, Granell LB, Cadilla CL, López-Garriga J. Recombinant hemoglobin II from Lucina pectinata: a large-scale method for hemeprotein expression in E. coli. Protein J 2010; 29:143-51. [PMID: 20221789 PMCID: PMC2873899 DOI: 10.1007/s10930-010-9234-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Hemoglobin II from the clam L. pectinata is an O(2) reactive protein that remains oxygenated in the presence of other molecules. To determine the mechanism of ligand selection in this hemoglobin, rHbII was expressed in large quantities using an improved fermentation process. The highest protein yield was obtained by: transforming HbII into the BLi5 cells, inducing and supplementing the culture during the mid-log phase with 1 mM IPTG, 30 microg/mL hemin chloride and 1% glucose, and decreasing the temperature to 30 degrees C after induction. In addition, cell culture density was greatly enhanced by using glycerol, adding MgSO(4), supplementing the media with glucose after the glycerol was consumed and maintaining the dissolved oxygen at 35%. Under these conditions the maximum protein yield obtained was approximately 2,300 mg/L. The results indicate that rHbII is similar to the native protein. The protocol was validated with other hemoglobins, indicating that it can be extended to other hemeproteins.
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Affiliation(s)
- Cacimar Ramos
- Department of Chemistry, University of Puerto Rico, Mayagüez Campus, PO BOX 9019, Mayagüez, PR 00681-9019, USA
| | - Ruth Pietri
- Department of Chemistry, University of Puerto Rico, Mayagüez Campus, PO BOX 9019, Mayagüez, PR 00681-9019, USA
| | - Wilmarie Lorenzo
- Department of Chemistry, University of Puerto Rico, Mayagüez Campus, PO BOX 9019, Mayagüez, PR 00681-9019, USA
| | - Elddie Roman
- Department of Chemistry, University of Puerto Rico, Mayagüez Campus, PO BOX 9019, Mayagüez, PR 00681-9019, USA
| | - Laura B. Granell
- Department of Chemistry, University of Puerto Rico, Mayagüez Campus, PO BOX 9019, Mayagüez, PR 00681-9019, USA
| | - Carmen L. Cadilla
- Department of Biochemistry, School of Medicine, University of Puerto Rico, Medical Sciences Campus, PO BOX 365067, San Juan, PR 00936-5067, USA
| | - Juan López-Garriga
- Department of Chemistry, University of Puerto Rico, Mayagüez Campus, PO BOX 9019, Mayagüez, PR 00681-9019, USA
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Molecular dynamics simulation of a carboxy murine neuroglobin mutated on the proximal side: heme displacement and concomitant rearrangement in loop regions. J Mol Model 2009; 16:759-70. [DOI: 10.1007/s00894-009-0581-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2009] [Accepted: 08/17/2009] [Indexed: 11/26/2022]
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Pietri R, Lewis A, León RG, Casabona G, Kiger L, Yeh SR, Fernandez-Alberti S, Marden MC, Cadilla CL, López-Garriga J. Factors controlling the reactivity of hydrogen sulfide with hemeproteins. Biochemistry 2009; 48:4881-94. [PMID: 19368335 DOI: 10.1021/bi801738j] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Hemoglobin I (HbI) from the clam Lucina pectinata is an intriguing hemeprotein that binds and transports H(2)S to sulfide-oxidizing chemoautotrophic bacteria to maintain a symbiotic relationship and to protect the mollusk from H(2)S toxicity. Single point mutations at E7, B10, and E11 were introduced into the HbI heme pocket to define the reactivity of sulfide with hemeproteins. The functional and structural properties of mutant and wild-type recombinant proteins were first evaluated using the well-known ferrous CO and O(2) derivatives. The effects of these mutations on the ferric environment were then studied in the metaquo and hydrogen sulfide derivatives. The results obtained with the ferrous HbI mutants show that all the E7 substitutions and the PheB10Tyr mutation influence directly CO and O(2) binding and stability while the B10 and E11 substitutions induce distal structural rearrangements that affect ligand entry and escape indirectly. For the metaquo-GlnE7His, -PheB10Val, -PheB10Leu, and -E11 variants, two individual distal structures are suggested, one of which is associated with H-bonding interactions between the E7 residues and the bound water. Similar H-bonding interactions are invoked for these HbI-H(2)S mutant derivatives and the rHbI, altering in turn sulfide reactivity within these protein samples. This is evident in the resonance Raman spectra of these HbI-H(2)S complexes, which show reduction of heme iron as judged by the appearance of the nu(4) oxidation state marker at 1356 cm(-1), indicative of heme-Fe(II) species. This reduction process depends strongly on distal mutations showing faster reduction for those HbI mutants exhibiting the strongest H-bonding interactions. Overall, the results presented here show that (a) H(2)S association is regulated by external kinetic barriers, (b) H(2)S release is controlled by two competing reactions involving simple sulfide dissociation and heme reduction, (c) at high H(2)S concentrations, reduction of the ferric center dominates, and (d) reduction of the heme is also enhanced in those HbI mutants having polar distal environments.
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Affiliation(s)
- Ruth Pietri
- Department of Chemistry, University of Puerto Rico, Mayaguez Campus, P.O. Box 9019, Mayaguez, Puerto Rico 00681-9019
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47
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Salter MD, Nienhaus K, Nienhaus GU, Dewilde S, Moens L, Pesce A, Nardini M, Bolognesi M, Olson JS. The apolar channel in Cerebratulus lacteus hemoglobin is the route for O2 entry and exit. J Biol Chem 2008; 283:35689-702. [PMID: 18840607 PMCID: PMC2602902 DOI: 10.1074/jbc.m805727200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2008] [Revised: 09/08/2008] [Indexed: 11/06/2022] Open
Abstract
The major pathway for O2 binding to mammalian myoglobins (Mb) and hemoglobins (Hb) involves transient upward movement of the distal histidine (His-64(E7)), allowing ligand capture in the distal pocket. The mini-globin from Cerebratulus lacteus (CerHb) appears to have an alternative pathway between the E and H helices that is made accessible by loss of the N-terminal A helix. To test this pathway, we examined the effects of changing the size of the E7 gate and closing the end of the apolar channel in CerHb by site-directed mutagenesis. Increasing the size of Gln-44(E7) from Ala to Trp causes variation of association (k'O2) and dissociation (kO2) rate coefficients, but the changes are not systematic. More significantly, the fractions (Fgem approximately 0.05-0.19) and rates (kgem approximately 50-100 micros(-1)) of geminate CO recombination in the Gln-44(E7) mutants are all similar. In contrast, blocking the entrance to the apolar channel by increasing the size of Ala-55(E18) to Phe and Trp causes the following: 1) both k'O2 and kO2 to decrease roughly 4-fold; 2) Fgem for CO to increase from approximately 0.05 to 0.45; and 3) kgem to decrease from approximately 80 to approximately 9 micros(-1), as ligands become trapped in the channel. Crystal structures and low temperature Fourier-transform infrared spectra of Phe-55 and Trp-55 CerHb confirm that the aromatic side chains block the channel entrance, with little effect on the distal pocket. These results provide unambiguous experimental proof that diatomic ligands can enter and exit a globin through an interior channel in preference to the more direct E7 pathway.
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Affiliation(s)
- Mallory D Salter
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892, USA
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48
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Brindell M, Stawoska I, Orzeł L, Labuz P, Stochel G, van Eldik R. Application of high pressure laser flash photolysis in studies on selected hemoprotein reactions. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1784:1481-92. [PMID: 18778796 DOI: 10.1016/j.bbapap.2008.08.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2008] [Revised: 07/14/2008] [Accepted: 08/04/2008] [Indexed: 12/31/2022]
Abstract
This article focuses on the application of high pressure laser flash photolysis for studies on selected hemoprotein reactions with the objective to establish details of the underlying reaction mechanisms. In this context, particular attention is given to the reactions of small molecules such as dioxygen, carbon monoxide, and nitric oxide with selected hemoproteins (hemoglobin, myoglobin, neuroglobin and cytochrome P450(cam)), as well as to photo-induced electron transfer reactions occurring in hemoproteins (particularly in various types of cytochromes). Mechanistic conclusions based on the interpretation of the obtained activation volumes are discussed in this account.
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Affiliation(s)
- Małgorzata Brindell
- Department of Inorganic Chemistry, Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow, Poland
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49
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Ouellet YH, Daigle R, Lagüe P, Dantsker D, Milani M, Bolognesi M, Friedman JM, Guertin M. Ligand binding to truncated hemoglobin N from Mycobacterium tuberculosis is strongly modulated by the interplay between the distal heme pocket residues and internal water. J Biol Chem 2008; 283:27270-8. [PMID: 18676995 DOI: 10.1074/jbc.m804215200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The survival of Mycobacterium tuberculosis requires detoxification of host *NO. Oxygenated Mycobacterium tuberculosis truncated hemoglobin N catalyzes the rapid oxidation of nitric oxide to innocuous nitrate with a second-order rate constant (k'(NOD) approximately 745 x 10(6) m(-1) x s(-1)), which is approximately 15-fold faster than the reaction of horse heart myoglobin. We ask what aspects of structure and/or dynamics give rise to this enhanced reactivity. A first step is to expose what controls ligand/substrate binding to the heme. We present evidence that the main barrier to ligand binding to deoxy-truncated hemoglobin N (deoxy-trHbN) is the displacement of a distal cavity water molecule, which is mainly stabilized by residue Tyr(B10) but not coordinated to the heme iron. As observed in the Tyr(B10)/Gln(E11) apolar mutants, once this kinetic barrier is lowered, CO and O(2) binding is very rapid with rates approaching 1-2 x 10(9) m(-1) x s(-1). These large values almost certainly represent the upper limit for ligand binding to a heme protein and also indicate that the iron atom in trHbN is highly reactive. Kinetic measurements on the photoproduct of the *NO derivative of met-trHbN, where both the *NO and water can be directly followed, revealed that water rebinding is quite fast (approximately 1.49 x 10(8) s(-1)) and is responsible for the low geminate yield in trHbN. Molecular dynamics simulations, performed with trHbN and its distal mutants, indicated that in the absence of a distal water molecule, ligand access to the heme iron is not hindered. They also showed that a water molecule is stabilized next to the heme iron through hydrogen-bonding with Tyr(B10) and Gln(E11).
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Affiliation(s)
- Yannick H Ouellet
- Department of Biochemistry and Microbiology, Laval University, Quebec, Canada, G1K 7P4
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Piubelli L, Pedotti M, Molla G, Feindler-Boeckh S, Ghisla S, Pilone MS, Pollegioni L. On the oxygen reactivity of flavoprotein oxidases: an oxygen access tunnel and gate in brevibacterium sterolicum cholesterol oxidase. J Biol Chem 2008; 283:24738-47. [PMID: 18614534 DOI: 10.1074/jbc.m802321200] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The flavoprotein cholesterol oxidase from Brevibacterium sterolicum (BCO) possesses a narrow channel that links the active center containing the flavin to the outside solvent. This channel has been proposed to serve for the access of dioxygen; it contains at its "bottom" a Glu-Arg pair (Glu-475-Arg-477) that was found by crystallographic studies to exist in two forms named "open" and "closed," which in turn was suggested to constitute a gate functioning in the control of oxygen access. Most mutations of residues that flank the channel have minor effects on the oxygen reactivity. Mutations of Glu-311, however, cause a switch in the basic kinetic mechanism of the reaction of reduced BCO with dioxygen; wild-type BCO and most mutants show a saturation behavior with increasing oxygen concentration, whereas for Glu-311 mutants a linear dependence is found that is assumed to reflect a "simple" second order process. This is taken as support for the assumption that residue Glu-311 finely tunes the Glu-475-Arg-477 pair, forming a gate that functions in modulating the access/reactivity of dioxygen.
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Affiliation(s)
- Luciano Piubelli
- Department of Biotechnology and Molecular Sciences, University of Insubria, 21100 Varese, Italy
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