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Lecomte JTJ, Johnson EA. The globins of cyanobacteria and green algae: An update. Adv Microb Physiol 2024; 85:97-144. [PMID: 39059824 DOI: 10.1016/bs.ampbs.2024.04.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/28/2024]
Abstract
The globin superfamily of proteins is ancient and diverse. Regular assessments based on the increasing number of available genome sequences have elaborated on a complex evolutionary history. In this review, we present a summary of a decade of advances in characterising the globins of cyanobacteria and green algae. The focus is on haem-containing globins with an emphasis on recent experimental developments, which reinforce links to nitrogen metabolism and nitrosative stress response in addition to dioxygen management. Mention is made of globins that do not bind haem to provide an encompassing view of the superfamily and perspective on the field. It is reiterated that an effort toward phenotypical and in-vivo characterisation is needed to elucidate the many roles that these versatile proteins fulfil in oxygenic photosynthetic microbes. It is also proposed that globins from oxygenic organisms are promising proteins for applications in the biotechnology arena.
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Affiliation(s)
- Juliette T J Lecomte
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD, United States.
| | - Eric A Johnson
- Department of Biology, Johns Hopkins University, Baltimore, MD, United States
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2
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Solomon LA, Witten J, Kodali G, Moser CC, Dutton PL. Tailorable Tetrahelical Bundles as a Toolkit for Redox Studies. J Phys Chem B 2022; 126:8177-8187. [PMID: 36219580 PMCID: PMC9589594 DOI: 10.1021/acs.jpcb.2c05119] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Oxidoreductases have evolved over millions of years to perform a variety of metabolic tasks crucial for life. Understanding how these tasks are engineered relies on delivering external electron donors or acceptors to initiate electron transfer reactions. This is a challenge. Small-molecule redox reagents can act indiscriminately, poisoning the cell. Natural redox proteins are more selective, but finding the right partner can be difficult due to the limited number of redox potentials and difficulty tuning them. De novo proteins offer an alternative path. They are robust and can withstand mutations that allow for tailorable changes. They are also devoid of evolutionary artifacts and readily bind redox cofactors. However, no reliable set of engineering principles have been developed that allow for these proteins to be fine-tuned so their redox midpoint potential (Em) can form donor/acceptor pairs with any natural oxidoreductase. This work dissects protein-cofactor interactions that can be tuned to modulate redox potentials of acceptors and donors using a mutable de novo designed tetrahelical protein platform with iron tetrapyrrole cofactors as a test case. We show a series of engineered heme b-binding de novo proteins and quantify their resulting effect on Em. By focusing on the surface charge and buried charges, as well as cofactor placement, chemical modification, and ligation of cofactors, we are able to achieve a broad range of Em values spanning a range of 330 mV. We anticipate this work will guide the design of proteinaceous tools that can interface with natural oxidoreductases inside and outside the cell while shedding light on how natural proteins modulate Em values of bound cofactors.
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Affiliation(s)
- Lee A. Solomon
- Department
of Chemistry and Biochemistry, George Mason
University, Fairfax, Virginia22030, United States,
| | - Joshua Witten
- Department
of Biology, George Mason University, Fairfax, Virginia22030, United States
| | - Goutham Kodali
- Department
of Biochemistry and Biophysics, University
of Pennsylvania, Philadelphia, Pennsylvania19104, United States
| | - Christopher C. Moser
- Department
of Biochemistry and Biophysics, University
of Pennsylvania, Philadelphia, Pennsylvania19104, United States
| | - P. Leslie Dutton
- Department
of Biochemistry and Biophysics, University
of Pennsylvania, Philadelphia, Pennsylvania19104, United States
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3
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Sandland J, Rimmer SD, Savoie H, Boyle RW. Bio-Orthogonal Conjugation of a Cationic Metalloporphyrin to BSA and HSA via "Click" Chemistry. Chembiochem 2021; 22:2624-2631. [PMID: 34096676 DOI: 10.1002/cbic.202100176] [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: 04/13/2021] [Revised: 06/02/2021] [Indexed: 11/11/2022]
Abstract
In this study, we present a convenient method for the labelling of tyrosine residues on bovine serum albumin (BSA) and human serum albumin (HSA) and report for the first time their subsequent bio-orthogonal conjugation with porphyrins via "click" chemistry. We demonstrate that these serum proteins can be labelled with an alkyne-diazonium heterobifunctional linker and can then undergo chemo-selective bio-orthogonal conjugation with a water-soluble azido metalloporphyrin via "click" chemistry to yield protein-conjugates that retain their photodynamic properties. In our hands, this method was found to be highly reproducible, scalable, and tuneable which allows for the production of bioconjugates where the porphyrin-protein conjugate not only retains an ability to generate singlet oxygen but possess an enhanced relative singlet oxygen quantum yields relative to the porphyrin alone. Furthermore, we have investigated the photochemical properties of these conjugates through photospectrometric techniques and have determined that the porphyrin macrocycles remain appreciably photostable under light irradiation. Our phototoxic protein-photosensitizer-conjugates show excellent photodynamic activity against a human colorectal adenocarcinoma cancer cell line (HT-29) with cell viabilities of 7.7±0.5 % (IC50 8.76±2.14 μM) and 1.7±1.9 % (IC50 8.48±5.11 μM) for BSA and HAS, respectively, when irradiated with 20 J cm-2 of white-light. Importantly, neither of the conjugates was found to possess any significant "dark" toxicity even at concentrations of 100 μM. Furthermore, the natural fluorescent properties of the bioconjugates allowed for the determination of cellular uptake in vitro via fluorescence microscopy thus highlighting the potential theranostic applications of these unique protein-drug-conjugates.
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Affiliation(s)
- Jordon Sandland
- Department of Chemistry and Biochemistry, University of Hull, Cottingham Road, Hull, E. Yorkshire, HU6 7RX, UK
| | - Sam D Rimmer
- Department of Chemistry and Biochemistry, University of Hull, Cottingham Road, Hull, E. Yorkshire, HU6 7RX, UK
| | - Huguette Savoie
- Department of Chemistry and Biochemistry, University of Hull, Cottingham Road, Hull, E. Yorkshire, HU6 7RX, UK
| | - Ross W Boyle
- Department of Chemistry and Biochemistry, University of Hull, Cottingham Road, Hull, E. Yorkshire, HU6 7RX, UK
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5
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Control of distal lysine coordination in a monomeric hemoglobin: A role for heme peripheral interactions. J Inorg Biochem 2021; 219:111437. [PMID: 33892380 DOI: 10.1016/j.jinorgbio.2021.111437] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Revised: 03/20/2021] [Accepted: 03/20/2021] [Indexed: 12/25/2022]
Abstract
THB1 is a monomeric truncated hemoglobin (TrHb) found in the cytoplasm of the green alga Chlamydomonas reinhardtii. The canonical heme coordination scheme in hemoglobins is a proximal histidine ligand and an open distal site. In THB1, the latter site is occupied by Lys53, which is likely to facilitate Fe(II)/Fe(III) redox cycling but hinders dioxygen binding, two features inherent to the NO dioxygenase activity of the protein. TrHb surveys show that a lysine at a position aligning with Lys53 is an insufficient determinant of coordination, and in this study, we sought to identify factors controlling lysine affinity for the heme iron. We solved the "Lys-off" X-ray structure of THB1, represented by the cyanide adduct of the Fe(III) protein, and hypothesized that interactions that differ between the known "Lys-on" structure and the Lys-off structure participate in the control of Lys53 affinity for the heme iron. We applied an experimental approach (site-directed mutagenesis, heme modification, pH titrations in the Fe(III) and Fe(II) states) and a computational approach (MD simulations in the Fe(II) state) to assess the role of heme propionate-protein interactions, distal helix capping, and the composition of the distal pocket. All THB1 modifications resulted in a weakening of lysine affinity and affected the coupling between Lys53 proton binding and heme redox potential. The results supported the importance of specific heme peripheral interactions for the pH stability of iron coordination and the ability of the protein to undergo redox reactions.
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6
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Hua X, Wang Z, Wang Z, Chen L, Zhou Z, Ouyang J, Deng K, Yang X, Huang H. De Novo Development of a Universal Biosensing Platform by Rapid Direct Native Protein Modification. Anal Chem 2021; 93:5291-5300. [PMID: 33734672 DOI: 10.1021/acs.analchem.1c00341] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An innovative biosensing assay was developed for simplified, cost-effective, and sensitive detection. By rapid, direct treatment of target proteins with iron porphyrin (TPPFe) in situ, a carboxyl group of amino acid conjugates with an Fe atom of the TPPFe molecule, forming a stable protein complex. We have shown that this complex not only maintains the integrity and functions of original proteins but also acquires peroxidase activity that can turn TMB to a comparably visible signal like that in ELISA. This study is unique since such conversion is difficult to achieve with standard chemical modification or molecular biology methods. In addition, the proposed immunoassay is superior to traditional ELISA as it eliminates an expensive and complicated cross-linking process of an enzyme-labeled antibody. From a practical point of view, we extended this assay to rapid detection of clinically relevant proteins and glucose in blood samples. The results show that this simple immunoassay provides clinical diagnosis, food safety, and environmental monitoring in an easy-to-implement manner.
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Affiliation(s)
- Xinyi Hua
- Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Ministry of Education, Hunan University of Science and Technology, Xiangtan 411201, China.,Hunan Provincial Key Laboratory of Controllable Preparation and Functional Application of Fine Polymers, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
| | - Zhifang Wang
- Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Ministry of Education, Hunan University of Science and Technology, Xiangtan 411201, China.,Hunan Provincial Key Laboratory of Controllable Preparation and Functional Application of Fine Polymers, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
| | - Ziqi Wang
- Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Ministry of Education, Hunan University of Science and Technology, Xiangtan 411201, China.,Hunan Provincial Key Laboratory of Controllable Preparation and Functional Application of Fine Polymers, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
| | - Linlin Chen
- Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Ministry of Education, Hunan University of Science and Technology, Xiangtan 411201, China.,Hunan Provincial Key Laboratory of Controllable Preparation and Functional Application of Fine Polymers, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
| | - Zaichun Zhou
- Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Ministry of Education, Hunan University of Science and Technology, Xiangtan 411201, China.,Hunan Provincial Key Laboratory of Controllable Preparation and Functional Application of Fine Polymers, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
| | - Junlin Ouyang
- School of Computer Science and Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
| | - Keqin Deng
- Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Ministry of Education, Hunan University of Science and Technology, Xiangtan 411201, China.,Hunan Provincial Key Laboratory of Controllable Preparation and Functional Application of Fine Polymers, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
| | - Xiumei Yang
- Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Ministry of Education, Hunan University of Science and Technology, Xiangtan 411201, China.,Hunan Provincial Key Laboratory of Controllable Preparation and Functional Application of Fine Polymers, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
| | - Haowen Huang
- Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Ministry of Education, Hunan University of Science and Technology, Xiangtan 411201, China.,Hunan Provincial Key Laboratory of Controllable Preparation and Functional Application of Fine Polymers, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
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7
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Márquez I, Olloqui-Sariego JL, Molero M, Andreu R, Roldán E, Calvente JJ. Active Role of the Buffer in the Proton-Coupled Electron Transfer of Immobilized Iron Porphyrins. Inorg Chem 2021; 60:42-54. [PMID: 32568550 DOI: 10.1021/acs.inorgchem.0c01091] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Evaluation of the proton-coupled electron transfer thermodynamics of immobilized hemin is challenging due to the disparity of its electrochemical titration curves reported in the literature. Deviations from the one-electron, one-proton transfer at circumneutral pHs have been commonly ascribed to either the formation of dimeric species or the ionization of a second iron-bound water molecule. Herein, however, we report on non-idealities in the more acidic region, whose onset and extent vary with the nature and concentration of the commonly used phosphate and acetate buffers. It is shown that these deviations originate in the ligand-exchange binding between the oxidized aquo-hemin complex and the anionic components of the buffer, so that they are restricted to the pH interval where these forms coexist. A stepwise approach was developed to quantify unambiguously the apparent and intrinsic binding equilibrium constants. The apparent binding equilibrium constant exhibits a peak-shaped pH dependence, whose maximum is located at approximately the midpoint between the pKa of the iron-bound water and the first pKa of the buffer, and its magnitude is greater for the phosphate than for the acetate buffer. But strikingly, the opposite trend was found for the magnitude of the intrinsic binding equilibrium constants determined from the apparent ones, due to the different relative locations of the phosphoric and acetic pKa values with respect to that of the oxidized aquo-hemin. To probe the role of the heme propionic residues, a similar study was carried out with a propionic-free iron porphyrin containing eight ethyl residues. These substituents decrease the acidity of the iron-bound water, strengthen the iron(III)-acetate binding, weaken the iron(III)-dihydrogen phosphate binding, and enable the binding between iron(III) and monohydrogen phosphate, which was hampered in hemin by the presence of the negatively charged propionate residues. Overall, this work provides a more complete speciation of immobilized iron porphyrins under acidic conditions than previously considered, showing the substitutional lability of the aqua ligand in the oxidized state of the iron center and the reluctance of its hydroxyl counterpart to anion exchange. Knowledge of these redox- and pH-dependent bindings with the buffer components is crucial for a rigorous quantification of the proton-coupled electron transfer and the electrocatalytic activity of iron porphyrins.
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Affiliation(s)
- Inmaculada Márquez
- Departamento de Quı́mica Fı́sica, Universidad de Sevilla, C/Profesor Garcı́a Conzález, 1, 41012 Sevilla, Spain
| | - José Luis Olloqui-Sariego
- Departamento de Quı́mica Fı́sica, Universidad de Sevilla, C/Profesor Garcı́a Conzález, 1, 41012 Sevilla, Spain
| | - Miguel Molero
- Departamento de Quı́mica Fı́sica, Universidad de Sevilla, C/Profesor Garcı́a Conzález, 1, 41012 Sevilla, Spain
| | - Rafael Andreu
- Departamento de Quı́mica Fı́sica, Universidad de Sevilla, C/Profesor Garcı́a Conzález, 1, 41012 Sevilla, Spain
| | - Emilio Roldán
- Departamento de Quı́mica Fı́sica, Universidad de Sevilla, C/Profesor Garcı́a Conzález, 1, 41012 Sevilla, Spain
| | - Juan José Calvente
- Departamento de Quı́mica Fı́sica, Universidad de Sevilla, C/Profesor Garcı́a Conzález, 1, 41012 Sevilla, Spain
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8
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Deng Y, Weaver ML, Hoke KR, Pletneva EV. A Heme Propionate Staples the Structure of Cytochrome c for Methionine Ligation to the Heme Iron. Inorg Chem 2019; 58:14085-14106. [PMID: 31589413 DOI: 10.1021/acs.inorgchem.9b02111] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ligand-switch reactions at the heme iron are common in biological systems, but their mechanisms and the features of the polypeptide fold that support dual ligation are not well understood. In cytochrome c (cyt c), two low-stability loops (Ω-loop C and Ω-loop D) are connected by the heme propionate HP6. At alkaline pH, the native Met80 ligand from Ω-loop D switches to a Lys residue from the same loop. Deprotonation of an as yet unknown group triggers the alkaline transition. We have created the two cyt c variants T49V/K79G and T78V/K79G with altered connections of these two loops to HP6. Electronic absorption, NMR, and EPR studies demonstrate that at pH 7.4 ferric forms of these variants are Lys-ligated, whereas ferrous forms maintain the native Met80 ligation. Measurements of protein stability, cyclic voltammetry, pH-jump and gated electron-transfer kinetics have revealed that these Thr to Val substitutions greatly affect the alkaline transition in both ferric and ferrous proteins. The substitutions modify the stability of the Met-ligated species and reduction potentials of the heme iron. The kinetics of ligand-switch processes are also altered, and analyses of these effects implicate redox-dependent differences in metal-ligand interactions and the role of the protein dynamics, including cross-talk between the two Ω-loops. With the two destabilized variants, it is possible to map energy levels for the Met- and Lys-ligated species in both ferric and ferrous proteins and assess the role of the protein scaffold in redox-dependent preferences for these two ligands. The estimated shift in the heme iron reduction potential upon deprotonation of the "trigger" group is consistent with those associated with deprotonation of an HP, suggesting that HP6, on its own or as a part of a hydrogen-bonded cluster, is a likely "trigger" for the Met to Lys ligand switch.
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Affiliation(s)
- Yunling Deng
- Department of Chemistry , Dartmouth College , Hanover , New Hampshire 03755 , United States
| | - Madeline L Weaver
- Department of Chemistry and Biochemistry , Berry College , Mount Berry , Georgia 30149 , United States
| | - Kevin R Hoke
- Department of Chemistry and Biochemistry , Berry College , Mount Berry , Georgia 30149 , United States
| | - Ekaterina V Pletneva
- Department of Chemistry , Dartmouth College , Hanover , New Hampshire 03755 , United States
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9
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Jenner LP, Kurth JM, van Helmont S, Sokol KP, Reisner E, Dahl C, Bradley JM, Butt JN, Cheesman MR. Heme ligation and redox chemistry in two bacterial thiosulfate dehydrogenase (TsdA) enzymes. J Biol Chem 2019; 294:18002-18014. [PMID: 31467084 PMCID: PMC6879331 DOI: 10.1074/jbc.ra119.010084] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Revised: 08/26/2019] [Indexed: 01/04/2023] Open
Abstract
Thiosulfate dehydrogenases (TsdAs) are bidirectional bacterial di-heme enzymes that catalyze the interconversion of tetrathionate and thiosulfate at measurable rates in both directions. In contrast to our knowledge of TsdA activities, information on the redox properties in the absence of substrates is rather scant. To address this deficit, we combined magnetic CD (MCD) spectroscopy and protein film electrochemistry (PFE) in a study to resolve heme ligation and redox chemistry in two representative TsdAs. We examined the TsdAs from Campylobacter jejuni, a microaerobic human pathogen, and from the purple sulfur bacterium Allochromatium vinosum. In these organisms, the enzyme functions as a tetrathionate reductase and a thiosulfate oxidase, respectively. The active site Heme 1 in both enzymes has His/Cys ligation in the ferric and ferrous states and the midpoint potentials (Em) of the corresponding redox transformations are similar, −185 mV versus standard hydrogen electrode (SHE). However, fundamental differences are observed in the properties of the second, electron transferring, Heme 2. In C. jejuni, TsdA Heme 2 has His/Met ligation and an Em of +172 mV. In A. vinosum TsdA, Heme 2 reduction triggers a switch from His/Lys ligation (Em, −129 mV) to His/Met (Em, +266 mV), but the rates of interconversion are such that His/Lys ligation would be retained during turnover. In summary, our findings have unambiguously assigned Em values to defined axial ligand sets in TsdAs, specified the rates of Heme 2 ligand exchange in the A. vinosum enzyme, and provided information relevant to describing their catalytic mechanism(s).
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Affiliation(s)
- Leon P Jenner
- Centre for Molecular and Structural Biochemistry, School of Chemistry and School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom
| | - Julia M Kurth
- Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich Wilhelms Universität Bonn, D-53115 Bonn, Germany
| | - Sebastian van Helmont
- Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich Wilhelms Universität Bonn, D-53115 Bonn, Germany
| | - Katarzyna P Sokol
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Erwin Reisner
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Christiane Dahl
- Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich Wilhelms Universität Bonn, D-53115 Bonn, Germany
| | - Justin M Bradley
- Centre for Molecular and Structural Biochemistry, School of Chemistry and School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom
| | - Julea N Butt
- Centre for Molecular and Structural Biochemistry, School of Chemistry and School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom
| | - Myles R Cheesman
- Centre for Molecular and Structural Biochemistry, School of Chemistry and School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom
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10
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Nye DB, Lecomte JTJ. Replacement of the Distal Histidine Reveals a Noncanonical Heme Binding Site in a 2-on-2 Hemoglobin. Biochemistry 2018; 57:5785-5796. [PMID: 30213188 PMCID: PMC6217817 DOI: 10.1021/acs.biochem.8b00752] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Heme ligation in hemoglobin is typically assumed by the "proximal" histidine. Hydrophobic contacts, ionic interactions, and the ligation bond secure the heme between two α-helices denoted E and F. Across the hemoglobin superfamily, several proteins also use a "distal" histidine, making the native state a bis-histidine complex. The group 1 truncated hemoglobin from Synechocystis sp. PCC 6803, GlbN, is one such bis-histidine protein. Ferric GlbN, in which the distal histidine (His46 or E10) has been replaced with a leucine, though expected to bind a water molecule and yield a high-spin iron complex at neutral pH, has low-spin spectral properties. Here, we applied nuclear magnetic resonance and electronic absorption spectroscopic methods to GlbN modified with heme and amino acid replacements to identify the distal ligand in H46L GlbN. We found that His117, a residue located in the C-terminal portion of the protein and on the proximal side of the heme, is responsible for the formation of an alternative bis-histidine complex. Simultaneous coordination by His70 and His117 situates the heme in a binding site different from the canonical site. This new holoprotein form is achieved with only local conformational changes. Heme affinity in the alternative site is weaker than in the normal site, likely because of strained coordination and a reduced number of specific heme-protein interactions. The observation of an unconventional heme binding site has important implications for the interpretation of mutagenesis results and globin homology modeling.
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Affiliation(s)
- Dillon B. Nye
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD, 21218, United States
| | - Juliette T. J. Lecomte
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD, 21218, United States
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11
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Johnson EA, Russo MM, Nye DB, Schlessman JL, Lecomte JTJ. Lysine as a heme iron ligand: A property common to three truncated hemoglobins from Chlamydomonas reinhardtii. Biochim Biophys Acta Gen Subj 2018; 1862:2660-2673. [PMID: 30251657 DOI: 10.1016/j.bbagen.2018.08.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 08/06/2018] [Accepted: 08/08/2018] [Indexed: 12/20/2022]
Abstract
BACKGROUND The nuclear genome of Chlamydomonas reinhardtii encodes a dozen hemoglobins of the truncated lineage. Four of these, named THB1-4, contain a single ~130-residue globin unit. THB1, which is cytoplasmic and capable of nitric oxide dioxygenation activity, uses a histidine and a lysine as axial ligands to the heme iron. In the present report, we compared THB2, THB3, and THB4 to THB1 to gain structural and functional insights into algal globins. METHODS We inspected properties of the globin domains prepared by recombinant means through site-directed mutagenesis, electronic absorption, CD, and NMR spectroscopies, and X-ray crystallography. RESULTS Recombinant THB3, which lacks the proximal histidine but has a distal histidine, binds heme weakly. NMR data demonstrate that the recombinant domains of THB2 and THB4 coordinate the ferrous heme iron with the proximal histidine and a lysine from the distal helix. An X-ray structure of ferric THB4 confirms lysine coordination. THB1, THB2, and THB4 have reduction potentials between -65 and -100 mV, are capable of nitric oxide dioxygenation, are reduced at different rates by the diaphorase domain of C. reinhardtii nitrate reductase, and show different response to peroxide treatment. CONCLUSIONS Three single-domain C. reinhardtii hemoglobins use lysine as a distal heme ligand in both Fe(III) and Fe(II) oxidation states. This common feature is likely related to enzymatic activity in the management of reactive oxygen species. GENERAL SIGNIFICANCE Primary structure analysis of hemoglobins has limited power in the prediction of heme ligation. Experimental determination reveals variations in this essential property across the superfamily.
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Affiliation(s)
- Eric A Johnson
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, United States
| | - Miranda M Russo
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, United States
| | - Dillon B Nye
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, United States
| | - Jamie L Schlessman
- Chemistry Department, U.S. Naval Academy, Annapolis, MD 21402, United States
| | - Juliette T J Lecomte
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, United States.
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