1
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Yao H, Alli S, Liu L, Soldano A, Cooper A, Fontenot L, Verdin D, Battaile KP, Lovell S, Rivera M. The crystal structure of Acinetobacter baumannii bacterioferritin reveals a heteropolymer of bacterioferritin and ferritin subunits. Sci Rep 2024; 14:18242. [PMID: 39107474 PMCID: PMC11303784 DOI: 10.1038/s41598-024-69156-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2024] [Accepted: 08/01/2024] [Indexed: 08/10/2024] Open
Abstract
Iron storage proteins, e.g., vertebrate ferritin, and the ferritin-like bacterioferritin (Bfr) and bacterial ferritin (Ftn), are spherical, hollow proteins that catalyze the oxidation of Fe2+ at binuclear iron ferroxidase centers (FOC) and store the Fe3+ in their interior, thus protecting cells from unwanted Fe3+/Fe2+ redox cycling and storing iron at concentrations far above the solubility of Fe3+. Vertebrate ferritins are heteropolymers of H and L subunits with only the H subunits having FOC. Bfr and Ftn were thought to coexist in bacteria as homopolymers, but recent evidence indicates these molecules are heteropolymers assembled from Bfr and Ftn subunits. Despite the heteropolymeric nature of vertebrate and bacterial ferritins, structures have been determined only for recombinant proteins constituted by a single subunit type. Herein we report the structure of Acinetobacter baumannii bacterioferritin, the first structural example of a heteropolymeric ferritin or ferritin-like molecule, assembled from completely overlapping Ftn homodimers harboring FOC and Bfr homodimers devoid of FOC but binding heme. The Ftn homodimers function by catalyzing the oxidation of Fe2+ to Fe3+, while the Bfr homodimers bind a cognate ferredoxin (Bfd) which reduces the stored Fe3+ by transferring electrons via the heme, enabling Fe2+ mobilization to the cytosol for incorporation in metabolism.
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Affiliation(s)
- Huili Yao
- Department of Chemistry, Louisiana State University, Baton Rouge, 70803, USA
| | - Suliat Alli
- Department of Chemistry, Louisiana State University, Baton Rouge, 70803, USA
| | - Lijun Liu
- Protein Structure and X-Ray Crystallography Laboratory, University of Kansas, Lawrence, 66047, USA
| | - Anabel Soldano
- Department of Chemistry, Louisiana State University, Baton Rouge, 70803, USA
| | - Anne Cooper
- Protein Structure and X-Ray Crystallography Laboratory, University of Kansas, Lawrence, 66047, USA
| | - Leo Fontenot
- Department of Chemistry, Louisiana State University, Baton Rouge, 70803, USA
| | - Dristen Verdin
- Department of Chemistry, Louisiana State University, Baton Rouge, 70803, USA
| | | | - Scott Lovell
- Protein Structure and X-Ray Crystallography Laboratory, University of Kansas, Lawrence, 66047, USA.
| | - Mario Rivera
- Department of Chemistry, Louisiana State University, Baton Rouge, 70803, USA.
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2
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Eren E, Watts NR, Montecinos F, Wingfield PT. Encapsulated Ferritin-like Proteins: A Structural Perspective. Biomolecules 2024; 14:624. [PMID: 38927029 PMCID: PMC11202242 DOI: 10.3390/biom14060624] [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: 04/29/2024] [Revised: 05/23/2024] [Accepted: 05/24/2024] [Indexed: 06/28/2024] Open
Abstract
Encapsulins are self-assembling nano-compartments that naturally occur in bacteria and archaea. These nano-compartments encapsulate cargo proteins that bind to the shell's interior through specific recognition sequences and perform various metabolic processes. Encapsulation enables organisms to perform chemical reactions without exposing the rest of the cell to potentially harmful substances while shielding cargo molecules from degradation and other adverse effects of the surrounding environment. One particular type of cargo protein, the ferritin-like protein (FLP), is the focus of this review. Encapsulated FLPs are members of the ferritin-like protein superfamily, and they play a crucial role in converting ferrous iron (Fe+2) to ferric iron (Fe+3), which is then stored inside the encapsulin in mineralized form. As such, FLPs regulate iron homeostasis and protect organisms against oxidative stress. Recent studies have demonstrated that FLPs have tremendous potential as biosensors and bioreactors because of their ability to catalyze the oxidation of ferrous iron with high specificity and efficiency. Moreover, they have been investigated as potential targets for therapeutic intervention in cancer drug development and bacterial pathogenesis. Further research will likely lead to new insights and applications for these remarkable proteins in biomedicine and biotechnology.
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Affiliation(s)
| | | | | | - Paul T. Wingfield
- Protein Expression Laboratory, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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3
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Edholm F, Nandy A, Reinhardt CR, Kastner DW, Kulik HJ. Protein3D: Enabling analysis and extraction of metal-containing sites from the Protein Data Bank with molSimplify. J Comput Chem 2024; 45:352-361. [PMID: 37873926 DOI: 10.1002/jcc.27242] [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: 08/09/2023] [Revised: 09/27/2023] [Accepted: 10/03/2023] [Indexed: 10/25/2023]
Abstract
Metalloenzymes catalyze a wide range of chemical transformations, with the active site residues playing a key role in modulating chemical reactivity and selectivity. Unlike smaller synthetic catalysts, a metalloenzyme active site is embedded in a larger protein, which makes interrogation of electronic properties and geometric features with quantum mechanical calculations challenging. Here we implement the ability to fetch crystallographic structures from the Protein Data Bank and analyze the metal binding sites in the program molSimplify. We show the usefulness of the newly created protein3D class to extract the local environment around non-heme iron enzymes containing a two histidine motif and prepare 372 structures for quantum mechanical calculations. Our implementation of protein3D serves to expand the range of systems molSimplify can be used to analyze and will enable high-throughput study of metal-containing active sites in proteins.
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Affiliation(s)
- Freya Edholm
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Aditya Nandy
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Clorice R Reinhardt
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - David W Kastner
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Heather J Kulik
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
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4
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Rivera M. Mobilization of iron stored in bacterioferritin, a new target for perturbing iron homeostasis and developing antibacterial and antibiofilm molecules. J Inorg Biochem 2023; 247:112306. [PMID: 37451083 DOI: 10.1016/j.jinorgbio.2023.112306] [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: 05/05/2023] [Revised: 06/08/2023] [Accepted: 06/24/2023] [Indexed: 07/18/2023]
Abstract
Antibiotic resistance is a global public health threat. The care of chronic infections is complicated by bacterial biofilms. Biofilm embedded cells can be up to 1000-fold more tolerant to antibiotic treatment than planktonic cells. Antibiotic tolerance is a condition which does not involve mutation and enables bacteria to survive in the presence of antibiotics. The antibiotic tolerance of biofilm-cells often renders antibiotics ineffective, even against strains that do not carry resistance-impairing mutations. This review discusses bacterial iron homeostasis and the strategies being developed to target this bacterial vulnerability, with emphasis on a recently proposed approach which aims at targeting the iron storage protein bacterioferritin (Bfr) and its physiological partner, the ferredoxin Bfd. Bfr regulates cytosolic iron concentrations by oxidizing Fe2+ and storing Fe3+ in its internal cavity, and by forming a complex with Bfd to reduce Fe3+ in the internal cavity and release Fe2+ to the cytosol. Blocking the Bfr-Bfd complex in P. aeruginosa cells causes an irreversible accumulation of Fe3+ in BfrB and simultaneous cytosolic iron depletion, which leads to impaired biofilm maintenance and biofilm cell death. Recently discovered small molecule inhibitors of the Bfr-Bfd complex, which bind Bfr at the Bfd binding site, inhibit iron mobilization, and elicit biofilm cell death.
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Affiliation(s)
- Mario Rivera
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803, USA.
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5
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Rajapaksha N, Soldano A, Yao H, Donnarumma F, Kashipathy MM, Seibold S, Battaile KP, Lovell S, Rivera M. Pseudomonas aeruginosa Dps (PA0962) Functions in H 2O 2 Mediated Oxidative Stress Defense and Exhibits In Vitro DNA Cleaving Activity. Int J Mol Sci 2023; 24:4669. [PMID: 36902100 PMCID: PMC10002758 DOI: 10.3390/ijms24054669] [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: 01/31/2023] [Revised: 02/16/2023] [Accepted: 02/25/2023] [Indexed: 03/04/2023] Open
Abstract
We report the structural, biochemical, and functional characterization of the product of gene PA0962 from Pseudomonas aeruginosa PAO1. The protein, termed Pa Dps, adopts the Dps subunit fold and oligomerizes into a nearly spherical 12-mer quaternary structure at pH 6.0 or in the presence of divalent cations at neutral pH and above. The 12-Mer Pa Dps contains two di-iron centers at the interface of each subunit dimer, coordinated by conserved His, Glu, and Asp residues. In vitro, the di-iron centers catalyze the oxidation of Fe2+ utilizing H2O2 (not O2) as an oxidant, suggesting Pa Dps functions to aid P. aeruginosa to survive H2O2-mediated oxidative stress. In agreement, a P. aeruginosa Δdps mutant is significantly more susceptible to H2O2 than the parent strain. The Pa Dps structure harbors a novel network of Tyr residues at the interface of each subunit dimer between the two di-iron centers, which captures radicals generated during Fe2+ oxidation at the ferroxidase centers and forms di-tyrosine linkages, thus effectively trapping the radicals within the Dps shell. Surprisingly, incubating Pa Dps and DNA revealed unprecedented DNA cleaving activity that is independent of H2O2 or O2 but requires divalent cations and 12-mer Pa Dps.
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Affiliation(s)
- Nimesha Rajapaksha
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803, USA
| | - Anabel Soldano
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803, USA
| | - Huili Yao
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803, USA
| | - Fabrizio Donnarumma
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803, USA
| | - Maithri M. Kashipathy
- Protein Structure and X-ray Crystallography Laboratory, University of Kansas, 2034 Becker Dr., Lawrence, KS 66047, USA
| | - Steve Seibold
- Protein Structure and X-ray Crystallography Laboratory, University of Kansas, 2034 Becker Dr., Lawrence, KS 66047, USA
| | | | - Scott Lovell
- Protein Structure and X-ray Crystallography Laboratory, University of Kansas, 2034 Becker Dr., Lawrence, KS 66047, USA
| | - Mario Rivera
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803, USA
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6
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Parida A, Mohanty A, Raut RK, Padhy I, Behera RK. Modification of 4-Fold and B-Pores in Bacterioferritin from Mycobacterium tuberculosis Reveals Their Role in Fe 2+ Entry and Oxidoreductase Activity. Inorg Chem 2023; 62:178-191. [PMID: 36525578 DOI: 10.1021/acs.inorgchem.2c03156] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The self-assembled ferritin nanocages, nature's solution to iron toxicity and its low solubility, scavenge free iron to synthesize hydrated ferric oxyhydroxide mineral inside their central cavity by protein-mediated ferroxidase and hydrolytic/nucleation reactions. These complex processes in ferritin commence with the rapid influx of Fe2+ ions via the inter-subunit contact points (i.e., pores/channels). Investigation of these pores as Fe2+ uptake routes in ferritins remains a subject of intense research, in iron metabolism, toxicity, and bacterial pathogenesis, which are yet to be established in the bacterioferritin (BfrA) from Mycobacterium tuberculosis (Mtb). The electrostatic properties of this protein indicate that the 4-fold and B-pores might serve as potential Fe2+ entry routes. Therefore, in the current work, electrostatics at/along these pores was altered by site-directed mutagenesis to establish their role in Fe2+ uptake/oxidation (ferroxidase activity) in Mtb BfrA. Despite forming self-assembled protein nanocompartment, these 4-fold and B-pore variants exhibited partial loss of ferroxidase activity and lower accumulation of transient species, which not only indicated their role in Fe2+ entry but also suggested the existence of multiple pathways. Although the B-pore variants inhibited the rapid ferroxidase activity to a larger extent, they had minimal impact on their cage stability. The current work revealed the relative contribution of these pores toward rapid Fe2+ uptake/oxidation and cage stability, possibly as consequences of their differential symmetry, number of modified residues (at each pore), and heme content. Therefore, these findings may help to understand the role of these pores in iron acquisition and Mtb proliferation under iron-limiting conditions to control its pathogenesis.
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Affiliation(s)
- Akankshika Parida
- Department of Chemistry, National Institute of Technology, Rourkela, 769008Odisha, India
| | - Abhinav Mohanty
- Department of Chemistry, National Institute of Technology, Rourkela, 769008Odisha, India
| | - Rohit Kumar Raut
- Department of Chemistry, National Institute of Technology, Rourkela, 769008Odisha, India
| | - Ipsita Padhy
- Department of Chemistry, National Institute of Technology, Rourkela, 769008Odisha, India
| | - Rabindra K Behera
- Department of Chemistry, National Institute of Technology, Rourkela, 769008Odisha, India
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7
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Bacterioferritin nanocage: Structure, biological function, catalytic mechanism, self-assembly and potential applications. Biotechnol Adv 2022; 61:108057. [DOI: 10.1016/j.biotechadv.2022.108057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Revised: 10/24/2022] [Accepted: 10/26/2022] [Indexed: 11/22/2022]
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8
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Mohanty A, Parida A, Raut RK, Behera RK. Ferritin: A Promising Nanoreactor and Nanocarrier for Bionanotechnology. ACS BIO & MED CHEM AU 2022; 2:258-281. [PMID: 37101573 PMCID: PMC10114856 DOI: 10.1021/acsbiomedchemau.2c00003] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 04/28/2023]
Abstract
The essence of bionanotechnology lies in the application of nanotechnology/nanomaterials to solve the biological problems. Quantum dots and nanoparticles hold potential biomedical applications, but their inherent problems such as low solubility and associated toxicity due to their interactions at nonspecific target sites is a major concern. The self-assembled, thermostable, ferritin protein nanocages possessing natural iron scavenging ability have emerged as a potential solution to all the above-mentioned problems by acting as nanoreactor and nanocarrier. Ferritins, the cellular iron repositories, are hollow, spherical, symmetric multimeric protein nanocages, which sequester the excess of free Fe(II) and synthesize iron biominerals (Fe2O3·H2O) inside their ∼5-8 nm central cavity. The electrostatics and dynamics of the pore residues not only drives the natural substrate Fe2+ inside ferritin nanocages but also uptakes a set of other metals ions/counterions during in vitro synthesis of nanomaterial. The current review aims to report the recent developments/understanding on ferritin structure (self-assembly, surface/pores electrostatics, metal ion binding sites) and chemistry occurring inside these supramolecular protein cages (protein mediated metal ion uptake and mineralization/nanoparticle formation) along with its surface modification to exploit them for various nanobiotechnological applications. Furthermore, a better understanding of ferritin self-assembly would be highly useful for optimizing the incorporation of nanomaterials via the disassembly/reassembly approach. Several studies have reported the successful engineering of these ferritin protein nanocages in order to utilize them as potential nanoreactor for synthesizing/incorporating nanoparticles and as nanocarrier for delivering imaging agents/drugs at cell specific target sites. Therefore, the combination of nanoscience (nanomaterials) and bioscience (ferritin protein) projects several benefits for various applications ranging from electronics to medicine.
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9
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Maity B, Hishikawa Y, Lu D, Ueno T. Recent progresses in the accumulation of metal ions into the apo-ferritin cage: Experimental and theoretical perspectives. Polyhedron 2019. [DOI: 10.1016/j.poly.2019.03.048] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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10
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Punchi Hewage AND, Yao H, Nammalwar B, Gnanasekaran KK, Lovell S, Bunce RA, Eshelman K, Phaniraj SM, Lee MM, Peterson BR, Battaile KP, Reitz AB, Rivera M. Small Molecule Inhibitors of the BfrB-Bfd Interaction Decrease Pseudomonas aeruginosa Fitness and Potentiate Fluoroquinolone Activity. J Am Chem Soc 2019; 141:8171-8184. [PMID: 31038945 PMCID: PMC6535718 DOI: 10.1021/jacs.9b00394] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
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The iron storage
protein bacterioferritin (BfrB) is central to
bacterial iron homeostasis. The mobilization of iron from BfrB, which
requires binding by a cognate ferredoxin (Bfd), is essential to the
regulation of cytosolic iron levels in P. aeruginosa. This paper describes the structure-guided development of small
molecule inhibitors of the BfrB–Bfd protein–protein
interaction. The process was initiated by screening a fragment library
and followed by obtaining the structure of a fragment hit bound to
BfrB. The structural insights were used to develop a series of 4-(benzylamino)-
and 4-((3-phenylpropyl)amino)-isoindoline-1,3-dione analogs that selectively
bind BfrB at the Bfd binding site. Challenging P. aeruginosa cells with the 4-substituted isoindoline analogs revealed a dose-dependent
growth phenotype. Further investigation determined that the analogs
elicit a pyoverdin hyperproduction phenotype that is consistent with
blockade of the BfrB–Bfd interaction and ensuing irreversible
accumulation of iron in BfrB, with concomitant depletion of iron in
the cytosol. The irreversible accumulation of iron in BfrB prompted
by the 4-substituted isoindoline analogs was confirmed by visualization
of BfrB-iron in P. aeruginosa cell lysates separated
on native PAGE gels and stained for iron with Ferene S. Challenging P. aeruginosa cultures with a combination of commercial
fluoroquinolone and our isoindoline analogs results in significantly
lower cell survival relative to treatment with either antibiotic or
analog alone. Collectively, these findings furnish proof of concept
for the usefulness of small molecule probes designed to dysregulate
bacterial iron homeostasis by targeting a protein–protein interaction
pivotal for iron storage in the bacterial cell.
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Affiliation(s)
- Achala N D Punchi Hewage
- Department of Chemistry , University of Kansas , 2030 Becker Drive , Lawrence , Kansas 66047 , United States
| | - Huili Yao
- Department of Chemistry , Louisiana State University , 229A Choppin Hall , Baton Rouge , Louisiana 70803 , United States
| | - Baskar Nammalwar
- Department of Chemistry , Oklahoma State University , Stillwater , Oklahoma 74078 , United States
| | | | - Scott Lovell
- Protein Structure Laboratory , University of Kansas , 2034 Becker Drive , Lawrence , Kansas 66047 , United States
| | - Richard A Bunce
- Department of Chemistry , Oklahoma State University , Stillwater , Oklahoma 74078 , United States
| | - Kate Eshelman
- Department of Chemistry , University of Kansas , 2030 Becker Drive , Lawrence , Kansas 66047 , United States
| | - Sahishna M Phaniraj
- Department of Medicinal Chemistry , University of Kansas , 2034 Becker Drive , Lawrence , Kansas 66047 , United States
| | - Molly M Lee
- Department of Medicinal Chemistry , University of Kansas , 2034 Becker Drive , Lawrence , Kansas 66047 , United States
| | - Blake R Peterson
- Department of Medicinal Chemistry , University of Kansas , 2034 Becker Drive , Lawrence , Kansas 66047 , United States
| | - Kevin P Battaile
- IMCA-CAT , Hauptman Woodward Medical Research Institute , 9700 South Cass Avenue, Building 435A , Argonne , Illinois 60439 , United States
| | - Allen B Reitz
- Fox Chase Chemical Diversity Center, Inc. , 3805 Old Easton Road , Doylestown , Pennsylvania 18902 , United States
| | - Mario Rivera
- Department of Chemistry , Louisiana State University , 229A Choppin Hall , Baton Rouge , Louisiana 70803 , United States
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11
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Wijerathne H, Yao H, Wang Y, Lovell S, Battaile KP, Rivera M. Bfd, a New Class of [2Fe-2S] Protein That Functions in Bacterial Iron Homeostasis, Requires a Structural Anion Binding Site. Biochemistry 2018; 57:5533-5543. [PMID: 30183257 DOI: 10.1021/acs.biochem.8b00823] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Mobilization of iron from bacterioferritin (BfrB) requires specific interactions with a [2Fe-2S] ferredoxin (Bfd). Blocking the BfrB:Bfd interaction results in irreversible iron accumulation in BfrB and iron deficiency in the cytosol [Eshelman, K., et al. (2017) Metallomics 9, 646-659]. The only known Bfd structure, which was obtained in complex with BfrB (Protein Data Bank entry 4E6K ), indicated a new fold and suggested that the stability of Bfd is aided by an anion binding site consisting of R26, R29, and K46. We investigated the Bfd fold using site-directed mutagenesis, X-ray crystallography, and biochemistry in solution. The X-ray structure, which is nearly identical to that of Bfd in the BfrB:Bfd complex, shows that the [2Fe-2S] cluster preorganizes residues at the BfrB:Bfd interface into a structure complementary to the Bfd binding site on BfrB. Studies in solution showed rapid loss of the [2Fe-2S] cluster at a low ionic strength but higher stability with an increasing ionic strength, thus supporting a structural anion binding site. Structures of the R26E and R26E/K46Y mutants are nearly identical to that of Bfd, except for a new network of hydrogen bonds stabilizing the region encompassing the former anion binding site. The stability of the R26E and R26E/K46Y mutants, which is weakly and completely independent of solution ionic strength, respectively, corroborates that Bfd requires an anion binding site. The mutations, which caused only small changes to the strength of the BfrB:Bfd interaction and mobilization of iron from BfrB, indicate that the anion binding site in Bfd serves primarily a structural role.
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Affiliation(s)
- Harshani Wijerathne
- Department of Chemistry , University of Kansas , Multidisciplinary Research Building, 2030 Becker Drive , Lawrence , Kansas 66047 , United States
| | - Huili Yao
- Department of Chemistry , Louisiana State University , 229A Choppin Hall , Baton Rouge , Louisiana 70803 , United States
| | - Yan Wang
- Department of Chemistry , University of Kansas , Multidisciplinary Research Building, 2030 Becker Drive , Lawrence , Kansas 66047 , United States
| | - Scott Lovell
- Protein Structure Laboratory, Del Shankel Structural Biology Center , University of Kansas , 2034 Becker Drive , Lawrence , Kansas 66047 , United States
| | - Kevin P Battaile
- IMCA-CAT , Hauptman Woodward Medical Research Institute , 9700 South Cass Avenue, Building 435A , Argonne , Illinois 60439 , United States
| | - Mario Rivera
- Department of Chemistry , Louisiana State University , 229A Choppin Hall , Baton Rouge , Louisiana 70803 , United States
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12
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Eshelman K, Yao H, Punchi Hewage AND, Deay JJ, Chandler JR, Rivera M. Inhibiting the BfrB:Bfd interaction in Pseudomonas aeruginosa causes irreversible iron accumulation in bacterioferritin and iron deficiency in the bacterial cytosol. Metallomics 2018; 9:646-659. [PMID: 28318006 DOI: 10.1039/c7mt00042a] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Iron is an essential nutrient for bacteria but the reactivity of Fe2+ and the insolubility of Fe3+ present significant challenges to bacterial cells. Iron storage proteins contribute to ameliorating these challenges by oxidizing Fe2+ using O2 and H2O2 as electron acceptors, and by compartmentalizing Fe3+. Two types of iron-storage proteins coexist in bacteria, the ferritins (Ftn) and the heme-containing bacterioferritins (Bfr), but the reasons for their coexistence are largely unknown. P. aeruginosa cells harbor two iron storage proteins (FtnA and BfrB), but nothing is known about their relative contributions to iron homeostasis. Prior studies in vitro have shown that iron mobilization from BfrB requires specific interactions with a ferredoxin (Bfd), but the relevance of the BfrB:Bfd interaction to iron homeostasis in P. aeruginosa is unknown. In this work we explore the repercussions of (i) deleting the bfrB gene, and (ii) perturbing the BfrB:Bfd interaction in P. aeruginosa cells by either deleting the bfd gene or by replacing the wild type bfrB gene with a L68A/E81A double mutant allele in the P. aeruginosa chromosome. The effects of the mutations were evaluated by following the accumulation of iron in BfrB, analyzing levels of free and total intracellular iron, and by characterizing the ensuing iron homeostasis dysregulation phenotypes. The results reveal that P. aeruginosa accumulates iron mainly in BfrB, and that the nutrient does not accumulate in FtnA to detectable levels, even after deletion of the bfrB gene. Perturbing the BfrB:Bfd interaction causes irreversible flow of iron into BfrB, which leads to the accumulation of unusable intracellular iron while severely depleting the levels of free intracellular iron, which drives the cells to an acute iron starvation response despite harboring "normal" levels of total intracellular iron. These results are discussed in the context of a dynamic equilibrium between free cytosolic Fe2+ and Fe3+ compartmentalized in BfrB, which functions as a buffer to oppose rapid changes of free cytosolic iron. Finally, we also show that P. aeruginosa cells utilize iron stored in BfrB for growth in iron-limiting conditions, and that the utilization of BfrB-iron requires a functional BfrB:Bfd interaction.
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Affiliation(s)
- Kate Eshelman
- Department of Chemistry and R. N. Adams Institute for Bioanalytical Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr, Lawrence, KS 66047, USA.
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13
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Sala D, Ciambellotti S, Giachetti A, Turano P, Rosato A. Investigation of the Iron(II) Release Mechanism of Human H-Ferritin as a Function of pH. J Chem Inf Model 2017; 57:2112-2118. [DOI: 10.1021/acs.jcim.7b00306] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Davide Sala
- Magnetic
Resonance Center (CERM), University of Florence, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy
| | - Silvia Ciambellotti
- Magnetic
Resonance Center (CERM), University of Florence, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy
| | - Andrea Giachetti
- Consorzio Interuniversitario di Risonanze Magnetiche di Metallo Proteine, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy
| | - Paola Turano
- Magnetic
Resonance Center (CERM), University of Florence, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy
- Department
of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy
| | - Antonio Rosato
- Magnetic
Resonance Center (CERM), University of Florence, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy
- Department
of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy
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14
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Rivera M. Bacterioferritin: Structure, Dynamics, and Protein-Protein Interactions at Play in Iron Storage and Mobilization. Acc Chem Res 2017; 50:331-340. [PMID: 28177216 PMCID: PMC5358871 DOI: 10.1021/acs.accounts.6b00514] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Despite its essentiality to life, iron presents significant challenges to cells: the exceedingly low solubility of Fe3+ limits its bioavailability, and the reactivity of Fe2+ toward H2O2 is a source of the toxic hydroxyl radical (HO•). Consequently, cellular levels of free iron are highly regulated to ensure sufficiency while preventing iron-induced toxicity. Relatively little is known about the fate of iron in the bacterial cytosol or how cells balance the need for relatively high cytosolic iron concentrations with the potential toxicity of the nutrient. Iron storage proteins are integral to iron metabolism, and bacteria utilize two types of ferritin-like molecules to store iron, bacterial ferritin (Ftn) and bacterioferritin (Bfr). Ftn and Bfr compartmentalize iron at concentrations far above the solubility of Fe3+ and protect the reducing cell environment from unwanted Fe3+/Fe2+ redox cycling. This Account focuses on our laboratory's efforts to study iron storage proteins in the model bacterium Pseudomonas aeruginosa, an opportunistic pathogen. Prior to our studies, it was thought that P. aeruginosa cells relied on a single Bfr assembled from two distinct subunits coded by the bfrA and bfrB genes. It is now known that, like in most bacteria, two iron storage proteins coexist in P. aeruginosa cells, a bacterial Ftn (FtnA), coded by the ftnA (formerly bfrA) gene and a bacterioferritin (BfrB), coded by the bfrB gene. Studies with BfrB showed that Fe2+ oxidation occurs at ferroxidase centers (FCs), followed by gated translocation of Fe3+ to the interior cavity, a process that is, surprisingly, distinct from that observed with the extensively studied Bfr from Escherichia coli, where the FCs are stable and function only as a catalytic site for O2 reduction. Investigations with BfrB showed that the oxidation of Fe2+ at FCs and the internalization of Fe3+ depend on long-range cooperative motions, extending from 4-fold pores, via B-pores, into FCs. It remains to be seen whether similar studies with E. coli Bfr will reveal distinct cooperative motions contributing to the stability of its FCs. Mobilization of Fe3+ stored in BfrB requires interaction with a ferredoxin (Bfd), which transfers electrons to reduce Fe3+ in the internal cavity of BfrB for subsequent release of Fe2+. The structure of the BfrB/Bfd complex furnished the only known structure of a ferritin molecule in complex with a physiological protein partner. The BfrB/Bfd complex is stabilized by hot-spot residues in both proteins, which interweave into a highly complementary hot region. The hot-spot residues are conserved in the sequences of Bfr and Bfd proteins from a number of bacteria, indicating that the BfrB/Bfd interaction is of widespread significance in bacterial iron metabolism. The BfrB/Bfd structure also furnished the only known structure of a Bfd, which revealed a novel helix-turn-helix fold different from the β-strand and α-helix fold of plant and vertebrate [2Fe-2S]-ferredoxins. Bfds seem to be unique to bacteria; consequently, although mobilization of iron from eukaryotic ferritins may also be facilitated by protein-protein interactions, the nature of the protein that delivers electrons to the ferric core of eukaryotic ferritins remains unknown.
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Affiliation(s)
- Mario Rivera
- Department of Chemistry and Ralph N. Adams
Institute for Bioanalytical Chemistry, University of Kansas, 2030 Becker
Dr., Lawrence, Kansas 66047, United States
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15
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Abstract
Ferritins, the main intracellular iron storage proteins, have been studied for over 60 years, mainly focusing on the mammalian ones. This allowed the elucidation of the structure of these proteins and the mechanisms regulating their iron incorporation and mineralization. However, ferritin is present in most, although not all, eukaryotic cells, comprising monocellular and multicellular invertebrates and vertebrates. The aim of this review is to provide an update on the general properties of ferritins that are common to various eukaryotic phyla (except plants), and to give an overview on the structure, function and regulation of ferritins. An update on the animal models that were used to characterize H, L and mitochondrial ferritins is also provided. The data show that ferritin structure is highly conserved among different phyla. It exerts an important cytoprotective function against oxidative damage and plays a role in innate immunity, where it also contributes to prevent parenchymal tissue from the cytotoxicity of pro-inflammatory agonists released by the activation of the immune response activation. Less clear are the properties of the secretory ferritins expressed by insects and molluscs, which may be important for understanding the role played by serum ferritin in mammals.
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16
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Bradley JM, Le Brun NE, Moore GR. Ferritins: furnishing proteins with iron. J Biol Inorg Chem 2016; 21:13-28. [PMID: 26825805 PMCID: PMC4771812 DOI: 10.1007/s00775-016-1336-0] [Citation(s) in RCA: 86] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 01/06/2016] [Indexed: 12/04/2022]
Abstract
Ferritins are a superfamily of iron oxidation, storage and mineralization proteins found throughout the animal, plant, and microbial kingdoms. The majority of ferritins consist of 24 subunits that individually fold into 4-α-helix bundles and assemble in a highly symmetric manner to form an approximately spherical protein coat around a central cavity into which an iron-containing mineral can be formed. Channels through the coat at inter-subunit contact points facilitate passage of iron ions to and from the central cavity, and intrasubunit catalytic sites, called ferroxidase centers, drive Fe2+ oxidation and O2 reduction. Though the different members of the superfamily share a common structure, there is often little amino acid sequence identity between them. Even where there is a high degree of sequence identity between two ferritins there can be major differences in how the proteins handle iron. In this review we describe some of the important structural features of ferritins and their mineralized iron cores, consider how iron might be released from ferritins, and examine in detail how three selected ferritins oxidise Fe2+ to explore the mechanistic variations that exist amongst ferritins. We suggest that the mechanistic differences reflect differing evolutionary pressures on amino acid sequences, and that these differing pressures are a consequence of different primary functions for different ferritins.
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Affiliation(s)
- Justin M Bradley
- Center for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
| | - Nick E Le Brun
- Center for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
| | - Geoffrey R Moore
- Center for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK.
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17
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Wang Y, Yao H, Cheng Y, Lovell S, Battaile KP, Midaugh CR, Rivera M. Characterization of the Bacterioferritin/Bacterioferritin Associated Ferredoxin Protein-Protein Interaction in Solution and Determination of Binding Energy Hot Spots. Biochemistry 2015; 54:6162-75. [PMID: 26368531 PMCID: PMC4708090 DOI: 10.1021/acs.biochem.5b00937] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
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Mobilization
of iron stored in the interior cavity of BfrB requires
electron transfer from the [2Fe–2S] cluster in Bfd to the core
iron in BfrB. A crystal structure of the Pseudomonas
aeruginosa BfrB:Bfd complex revealed that BfrB can
bind up to 12 Bfd molecules at 12 structurally identical binding sites,
placing the [2Fe–2S] cluster of each Bfd immediately above
a heme group in BfrB [Yao, H., et al. (2012) J. Am. Chem.
Soc., 134, 13470–13481]. We report
here a study aimed at characterizing the strength of the P. aeruginosa BfrB:Bfd association using surface
plasmon resonance and isothermal titration calorimetry as well as
determining the binding energy hot spots at the protein–protein
interaction interface. The results show that the 12 Bfd-binding sites
on BfrB are equivalent and independent and that the protein–protein
association at each of these sites is driven entropically and is characterized
by a dissociation constant (Kd) of approximately
3 μM. Determination of the binding energy hot spots was carried
out by replacing certain residues that comprise the protein–protein
interface with alanine and by evaluating the effect of the mutation
on Kd and on the efficiency of core iron
mobilization from BfrB. The results identified hot spot residues in
both proteins [LB68, EA81, and
EA85 in BfrB
(superscript for residue number and subscript for chain) and Y2 and L5 in Bfd] that network at the interface to
produce a highly complementary hot region for the interaction. The
hot spot residues are conserved in the amino acid sequences of Bfr
and Bfd proteins from a number of Gram-negative pathogens, indicating
that the BfrB:Bfd interaction is of widespread significance in bacterial
iron metabolism.
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Affiliation(s)
- Yan Wang
- Department of Chemistry, University of Kansas , Multidisciplinary Research Building, 2030 Becker Drive, Room 220E, Lawrence, Kansas 66047, United States
| | - Huili Yao
- Department of Chemistry, University of Kansas , Multidisciplinary Research Building, 2030 Becker Drive, Room 220E, Lawrence, Kansas 66047, United States
| | - Yuan Cheng
- Department of Pharmaceutical Chemistry, University of Kansas , Multidisciplinary Research Building, 2030 Becker Drive, Room 320G, Lawrence, Kansas 66047, United States
| | - Scott Lovell
- Protein Structure Laboratory, Del Shankel Structural Biology Center, University of Kansas , 2034 Becker Drive, Lawrence, Kansas 66047, United States
| | - Kevin P Battaile
- IMCA-CAT, Hauptman Woodward Medical Research Institute , 9700 South Cass Avenue, Building 435A, Argonne, Illinois 60439, United States
| | - C Russell Midaugh
- Department of Pharmaceutical Chemistry, University of Kansas , Multidisciplinary Research Building, 2030 Becker Drive, Room 320G, Lawrence, Kansas 66047, United States
| | - Mario Rivera
- Department of Chemistry, University of Kansas , Multidisciplinary Research Building, 2030 Becker Drive, Room 220E, Lawrence, Kansas 66047, United States
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18
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Ebrahimi KH, Hagedoorn PL, Hagen WR. Self-assembly is prerequisite for catalysis of Fe(II) oxidation by catalytically active subunits of ferritin. J Biol Chem 2015; 290:26801-10. [PMID: 26370076 PMCID: PMC4646333 DOI: 10.1074/jbc.m115.678375] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Indexed: 12/16/2022] Open
Abstract
Fe(III) storage by ferritin is an essential process of the iron homeostasis machinery. It begins by translocation of Fe(II) from outside the hollow spherical shape structure of the protein, which is formed as the result of self-assembly of 24 subunits, to a di-iron binding site, the ferroxidase center, buried in the middle of each active subunit. The pathway of Fe(II) to the ferroxidase center has remained elusive, and the importance of self-assembly for the functioning of the ferroxidase center has not been investigated. Here we report spectroscopic and metal ion binding studies with a mutant of ferritin from Pyrococcus furiosus (PfFtn) in which self-assembly was abolished by a single amino acid substitution. We show that in this mutant metal ion binding to the ferroxidase center and Fe(II) oxidation at this site was obliterated. However, metal ion binding to a conserved third site (site C), which is located in the inner surface of each subunit in the vicinity of the ferroxidase center and is believed to be the path for Fe(II) to the ferroxidase center, was not disrupted. These results are the basis of a new model for Fe(II) translocation to the ferroxidase center: self-assembly creates channels that guide the Fe(II) ions toward the ferroxidase center directly through the protein shell and not via the internal cavity and site C. The results may be of significance for understanding the molecular basis of ferritin-related disorders such as neuroferritinopathy in which the 24-meric structure with 432 symmetry is distorted.
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Affiliation(s)
| | - Peter-Leon Hagedoorn
- From the Department of Biotechnology, Delft University of Technology, 2628 BC Delft, The Netherlands
| | - Wilfred R Hagen
- From the Department of Biotechnology, Delft University of Technology, 2628 BC Delft, The Netherlands
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