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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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2
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Pérez-Amigot D, Taleb V, Boneta S, Anoz-Carbonell E, Sebastián M, Velázquez-Campoy A, Polo V, Martínez-Júlvez M, Medina M. Towards the competent conformation for catalysis in the ferredoxin-NADP + reductase from the Brucella ovis pathogen. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2019; 1860:148058. [PMID: 31394095 DOI: 10.1016/j.bbabio.2019.148058] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2019] [Revised: 07/19/2019] [Accepted: 08/02/2019] [Indexed: 02/02/2023]
Abstract
Brucella ovis encodes a bacterial subclass 1 ferredoxin-NADP(H) reductase (BoFPR) that, by similarity with other FPRs, is expected either to deliver electrons from NADPH to the redox-based metabolism and/or to oxidize NADPH to regulate the soxRS regulon that protects bacteria against oxidative damage. Such potential roles for the pathogen survival under infection conditions make of interest to understand and to act on the BoFPR mechanism. Here, we investigate the NADP+/H interaction and NADPH oxidation by hydride transfer (HT) to BoFPR. Crystal structures of BoFPR in free and in complex with NADP+ hardly differ. The latter shows binding of the NADP+ adenosine moiety, while its redox-reactive nicotinamide protrudes towards the solvent. Nonetheless, pre-steady-state kinetics show formation of a charge-transfer complex (CTC-1) prior to the hydride transfer, as well as conversion of CTC-1 into a second charge-transfer complex (CTC-2) concomitantly with the HT event. Thus, during catalysis nicotinamide and flavin reacting rings stack. Kinetic data also identify the HT itself as the rate limiting step in the reduction of BoFPR by NADPH, as well as product release limiting the overall reaction. Using all-atom molecular dynamics simulations with a thermal effect approach we are able to visualise a potential transient catalytically competent interaction of the reacting rings. Simulations indicate that the architecture of the FAD folded conformation in BoFPR might be key in catalysis, pointing to its adenine as an element to orient the reactive atoms in conformations competent for HT.
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Affiliation(s)
- Daniel Pérez-Amigot
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain; Instituto de Biocomputación y Física de Sistemas Complejos (Joint Units: BIFI-IQFR and GBsC-CSIC), Universidad de Zaragoza, 50018 Zaragoza, Spain
| | - Víctor Taleb
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain; Instituto de Biocomputación y Física de Sistemas Complejos (Joint Units: BIFI-IQFR and GBsC-CSIC), Universidad de Zaragoza, 50018 Zaragoza, Spain
| | - Sergio Boneta
- Instituto de Biocomputación y Física de Sistemas Complejos (Joint Units: BIFI-IQFR and GBsC-CSIC), Universidad de Zaragoza, 50018 Zaragoza, Spain; Departamento de Química Física, Universidad de Zaragoza, 50009 Zaragoza, Spain
| | - Ernesto Anoz-Carbonell
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain; Instituto de Biocomputación y Física de Sistemas Complejos (Joint Units: BIFI-IQFR and GBsC-CSIC), Universidad de Zaragoza, 50018 Zaragoza, Spain
| | - María Sebastián
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain; Instituto de Biocomputación y Física de Sistemas Complejos (Joint Units: BIFI-IQFR and GBsC-CSIC), Universidad de Zaragoza, 50018 Zaragoza, Spain
| | - Adrián Velázquez-Campoy
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain; Instituto de Biocomputación y Física de Sistemas Complejos (Joint Units: BIFI-IQFR and GBsC-CSIC), Universidad de Zaragoza, 50018 Zaragoza, Spain; Aragon Institute for Health Research (IIS-Aragon), Zaragoza 50009, Spain; Biomedical Research Networking Center in Digestive and Hepatic Diseases (CIBERehd), Madrid, Spain; Fundacion ARAID, Government of Aragon, Zaragoza 50018, Spain
| | - Víctor Polo
- Instituto de Biocomputación y Física de Sistemas Complejos (Joint Units: BIFI-IQFR and GBsC-CSIC), Universidad de Zaragoza, 50018 Zaragoza, Spain; Departamento de Química Física, Universidad de Zaragoza, 50009 Zaragoza, Spain
| | - Marta Martínez-Júlvez
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain; Instituto de Biocomputación y Física de Sistemas Complejos (Joint Units: BIFI-IQFR and GBsC-CSIC), Universidad de Zaragoza, 50018 Zaragoza, Spain.
| | - Milagros Medina
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain; Instituto de Biocomputación y Física de Sistemas Complejos (Joint Units: BIFI-IQFR and GBsC-CSIC), Universidad de Zaragoza, 50018 Zaragoza, Spain.
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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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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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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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6
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Antonini LV, Peregrina JR, Angulo J, Medina M, Nieto PM. A STD-NMR study of the interaction of the Anabaena ferredoxin-NADP+ reductase with the coenzyme. Molecules 2014; 19:672-85. [PMID: 24402199 PMCID: PMC6272016 DOI: 10.3390/molecules19010672] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Revised: 12/17/2013] [Accepted: 12/18/2013] [Indexed: 11/16/2022] Open
Abstract
Ferredoxin-NADP+ reductase (FNR) catalyzes the electron transfer from ferredoxin to NADP+ via its flavin FAD cofactor. To get further insights in the architecture of the transient complexes produced during the hydride transfer event between the enzyme and the NADP+ coenzyme we have applied NMR spectroscopy using Saturation Transfer Difference (STD) techniques to analyze the interaction between FNRox and the oxidized state of its NADP+ coenzyme. We have found that STD NMR, together with the use of selected mutations on FNR and of the non-FNR reacting coenzyme analogue NAD+, are appropriate tools to provide further information about the the interaction epitope.
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Affiliation(s)
- Lara V Antonini
- Instituto de Investigaciones Químicas, CSIC, Americo Vespucio, 49, Sevilla 41092, Spain.
| | - José R Peregrina
- Instituto de Investigaciones Químicas, CSIC, Americo Vespucio, 49, Sevilla 41092, Spain.
| | - Jesús Angulo
- Instituto de Investigaciones Químicas, CSIC, Americo Vespucio, 49, Sevilla 41092, Spain.
| | - Milagros Medina
- Instituto de Investigaciones Químicas, CSIC, Americo Vespucio, 49, Sevilla 41092, Spain.
| | - Pedro M Nieto
- Instituto de Investigaciones Químicas, CSIC, Americo Vespucio, 49, Sevilla 41092, Spain.
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Crystal structure of the FAD-containing ferredoxin-NADP+ reductase from the plant pathogen Xanthomonas axonopodis pv. citri. BIOMED RESEARCH INTERNATIONAL 2013; 2013:906572. [PMID: 23984418 PMCID: PMC3747371 DOI: 10.1155/2013/906572] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Accepted: 07/07/2013] [Indexed: 11/17/2022]
Abstract
We have solved the structure of ferredoxin-NADP(H) reductase, FPR, from the plant pathogen Xanthomonas axonopodis pv. citri, responsible for citrus canker, at a resolution of 1.5 Å. This structure reveals differences in the mobility of specific loops when compared to other FPRs, probably unrelated to the hydride transfer process, which contributes to explaining the structural and functional divergence between the subclass I FPRs. Interactions of the C-terminus of the enzyme with the phosphoadenosine of the cofactor FAD limit its mobility, thus affecting the entrance of nicotinamide into the active site. This structure opens the possibility of rationally designing drugs against the X. axonopodis pv. citri phytopathogen.
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Abstract
All but a few bacterial species have an absolute need for heme, and most are able to synthesize it via a pathway that is highly conserved among all life domains. Because heme is a rich source for iron, many pathogenic bacteria have also evolved processes for sequestering heme from their hosts. The heme biosynthesis pathways are well understood at the genetic and structural biology levels. In comparison, much less is known about the heme acquisition, trafficking, and degradation processes in bacteria. Gram-positive and Gram-negative bacteria have evolved similar strategies but different tactics for importing and degrading heme, likely as a consequence of their different cellular architectures. The differences are manifested in distinct structures for molecules that perform similar functions. Consequently, the aim of this chapter is to provide an overview of the structural biology of proteins and protein-protein interactions that enable Gram-positive and Gram-negative bacteria to sequester heme from the extracellular milieu, import it to the cytosol, and degrade it to mine iron.
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Affiliation(s)
- David R Benson
- Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr., Lawrence, KS, 66047, USA,
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Yao H, Wang Y, Lovell S, Kumar R, Ruvinsky AM, Battaile KP, Vakser IA, Rivera M. The structure of the BfrB-Bfd complex reveals protein-protein interactions enabling iron release from bacterioferritin. J Am Chem Soc 2012; 134:13470-81. [PMID: 22812654 PMCID: PMC3428730 DOI: 10.1021/ja305180n] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Ferritin-like molecules are unique to cellular iron homeostasis because they can store iron at concentrations much higher than those dictated by the solubility of Fe(3+). Very little is known about the protein interactions that deliver iron for storage or promote the mobilization of stored iron from ferritin-like molecules. Here, we report the X-ray crystal structure of Pseudomonas aeruginosa bacterioferritin (Pa-BfrB) in complex with bacterioferritin-associated ferredoxin (Pa-Bfd) at 2.0 Å resolution. As the first example of a ferritin-like molecule in complex with a cognate partner, the structure provides unprecedented insight into the complementary interface that enables the [2Fe-2S] cluster of Pa-Bfd to promote heme-mediated electron transfer through the BfrB protein dielectric (~18 Å), a process that is necessary to reduce the core ferric mineral and facilitate mobilization of Fe(2+). The Pa-BfrB-Bfd complex also revealed the first structure of a Bfd, thus providing a first view to what appears to be a versatile metal binding domain ubiquitous to the large Fer2_BFD family of proteins and enzymes with diverse functions. Residues at the Pa-BfrB-Bfd interface are highly conserved in Bfr and Bfd sequences from a number of pathogenic bacteria, suggesting that the specific recognition between Pa-BfrB and Pa-Bfd is of widespread significance to the understanding of bacterial iron homeostasis.
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Affiliation(s)
- Huili Yao
- Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr., Lawrence, KS 66047
| | - Yan Wang
- Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr., Lawrence, KS 66047
| | - Scott Lovell
- Del Shankel Structural Biology Center, University of Kansas, 2034 Becker Dr., Lawrence, KS 66047
| | - Ritesh Kumar
- Center for Bioinformatics, University of Kansas, 2030 Becker Dr., Lawrence, KS 66047
| | - Anatoly M. Ruvinsky
- Center for Bioinformatics, University of Kansas, 2030 Becker Dr., Lawrence, KS 66047
| | - Kevin P. Battaile
- IMCA-CAT, Hauptman Woodward Medical Research Institute, 9700 S. Cass Avenue, Bldg. 435A, Argonne, IL 60439
| | - Ilya A. Vakser
- Center for Bioinformatics, University of Kansas, 2030 Becker Dr., Lawrence, KS 66047
| | - Mario Rivera
- Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr., Lawrence, KS 66047
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Musumeci MA, Botti H, Buschiazzo A, Ceccarelli EA. Swapping FAD binding motifs between plastidic and bacterial ferredoxin-NADP(H) reductases. Biochemistry 2011; 50:2111-22. [PMID: 21306142 DOI: 10.1021/bi101772a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Plant-type ferredoxin-NADP(H) reductases (FNRs) are grouped in two classes, plastidic with an extended FAD conformation and high catalytic rates and bacterial with a folded flavin nucleotide and low turnover rates. The 112-123 β-hairpin from a plastidic FNR and the carboxy-terminal tryptophan of a bacterial FNR, suggested to be responsible for the FAD differential conformation, were mutually exchanged. The plastidic FNR lacking the β-hairpin was unable to fold properly. An extra tryptophan at the carboxy terminus, emulating the bacterial FNR, resulted in an enzyme with decreased affinity for FAD and reduced diaphorase and ferredoxin-dependent cytochrome c reductase activities. The insertion of the β-hairpin into the corresponding position of the bacterial FNR increased FAD affinity but did not affect its catalytic properties. The same insertion with simultaneous deletion of the carboxy-terminal tryptophan produced a bacterial chimera emulating the plastidic architecture with an increased k(cat) and an increased catalytic efficiency for the diaphorase activity and a decrease in the enzyme's ability to react with its substrates ferredoxin and flavodoxin. Crystallographic structures of the chimeras showed no significant changes in their overall structure, although alterations in the FAD conformations were observed. Plastidic and bacterial FNRs thus reveal differential effects of key structural elements. While the 112-123 β-hairpin modulates the catalytic efficiency of plastidic FNR, it seems not to affect the bacterial FNR behavior, which instead can be improved by the loss of the C-terminal tryptophan. This report highlights the role of the FAD moiety conformation and the structural determinants involved in stabilizing it, ultimately modulating the functional output of FNRs.
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Affiliation(s)
- Matías A Musumeci
- Molecular Biology Division, Instituto de Biología Molecular y Celular de Rosario (IBR), CONICET, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina
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11
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Jepkorir G, Rodríguez JC, Rui H, Im W, Lovell S, Battaile KP, Alontaga AY, Yukl ET, Moënne-Loccoz P, Rivera M. Structural, NMR spectroscopic, and computational investigation of hemin loading in the hemophore HasAp from Pseudomonas aeruginosa. J Am Chem Soc 2010; 132:9857-72. [PMID: 20572666 PMCID: PMC2948407 DOI: 10.1021/ja103498z] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
When challenged by low-iron conditions several Gram-negative pathogens secrete a hemophore (HasA) to scavenge hemin from its host and deliver it to a receptor (HasR) on their outer membrane for internalization. Here we report results from studies aimed at probing the structural and dynamic processes at play in the loading of the apo-hemophore secreted by P. aeruginosa (apo-HasAp) with hemin. The structure of apo-HasAp shows a large conformational change in the loop harboring axial ligand His32 relative to the structure of holo-HasAp, whereas the loop bearing the other axial ligand, Tyr75, remains intact. To investigate the role played by the axial ligand-bearing loops in the process of hemin capture we investigated the H32A mutant, which was found to exist as a monomer in its apo-form and as a mixture of monomers and dimers in its holo-form. We obtained an X-ray structure of dimeric H32A holo-HasAp, which revealed that the two subunits are linked by cofacial interactions of two hemin molecules and that the conformation of the Ala32 loop in the dimer is identical to that exhibited by the His32 loop in wild type apo-HasAp. Additional data suggest that the conformation of the Ala32 loop in the dimer is mainly a consequence of dimerization. Hence, to investigate the effect of hemin loading on the topology of the His32 loop we also obtained the crystal structure of monomeric H32A holo-HasAp coordinated by imidazole (H32A-imidazole) and investigated the monomeric H32A HasAp and H32A-imidazole species in solution by NMR spectroscopy. The structure of H32A-imidazole revealed that the Ala32 loop attains a "closed" conformation nearly identical to that observed in wild type holo-HasAp, and the NMR investigations indicated that this conformation is maintained in solution. The NMR studies also highlighted conformational heterogeneity at the H32 loop hinges and in other key sections of the structure. Targeted molecular dynamics simulations allowed us to propose a possible path for the closing of the His32 loop upon hemin binding and identified molecular motions that are likely important in transmitting the presence of hemin in the Tyr75 loop to the His32 loop to initiate its closing. Importantly, residues implicated as undergoing motions in the computations are also observed as being dynamic by NMR. Taken together, these observations provide direct experimental evidence indicating that hemin loads onto the Tyr75 loop of apo-HasAp, which triggers the closing of the His32 loop.
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Affiliation(s)
- Grace Jepkorir
- Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr., room 220 E, Lawrence
| | - Juan Carlos Rodríguez
- Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr., room 220 E, Lawrence
| | - Huan Rui
- Department of Molecular Biosciences and Center for Bioinformatics, The University of Kansas, Lawrence, Kansas 66047
| | - Wonpil Im
- Department of Molecular Biosciences and Center for Bioinformatics, The University of Kansas, Lawrence, Kansas 66047
| | - Scott Lovell
- Del Shankel Structural Biology Center, University of Kansas, 2034 Becker Dr., Lawrence, KS 66047
| | - Kevin P. Battaile
- IMCA-CAT, Hauptman-Woodward Medical Research Institute, 9700 South Cass Avenue, Building 435A, Argonne, Il 60439
| | - Aileen Y. Alontaga
- Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr., room 220 E, Lawrence
| | - Erik T. Yukl
- Department of Science and Engineering, Oregon Health & Science University, Beaverton, Oregon 97006
| | - Pierre Moënne-Loccoz
- Department of Science and Engineering, Oregon Health & Science University, Beaverton, Oregon 97006
| | - Mario Rivera
- Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr., room 220 E, Lawrence
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Weeratunga SK, Gee CE, Lovell S, Zeng Y, Woodin CL, Rivera M. Binding of Pseudomonas aeruginosa apobacterioferritin-associated ferredoxin to bacterioferritin B promotes heme mediation of electron delivery and mobilization of core mineral iron. Biochemistry 2009; 48:7420-31. [PMID: 19575528 DOI: 10.1021/bi900561a] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The bfrB gene from Pseudomonas aeruginosa was cloned and expressed in Escherichia coli. The resultant protein (BfrB), which assembles into a 445.3 kDa complex from 24 identical subunits, binds 12 molecules of heme axially coordinated by two Met residues. BfrB, isolated with 5-10 iron atoms per protein molecule, was reconstituted with ferrous ions to prepare samples with a core mineral containing 600 +/- 40 ferric ions per BfrB molecule and approximately one phosphate molecule per iron atom. In the presence of sodium dithionite or in the presence of P. aeruginosa ferredoxin NADP reductase (FPR) and NADPH, the heme in BfrB remains oxidized, and the core iron mineral is mobilized sluggishly. In stark contrast, addition of NADPH to a solution containing BfrB, FPR, and the apo form of P. aeruginosa bacterioferritin-associated ferredoxin (apo-Bfd) results in rapid reduction of the heme in BfrB and in the efficient mobilization of the core iron mineral. Results from additional experimentation indicate that Bfd must bind to BfrB to promote heme mediation of electrons from the surface to the core to support the efficient mobilization of ferrous ions from BfrB. In this context, the thus far mysterious role of heme in bacterioferritins has been brought to the front by reconstituting BfrB with its physiological partner, apo-Bfd. These findings are discussed in the context of a model for the utilization of stored iron in which the significant upregulation of the bfd gene under low-iron conditions [Ochsner, U. A., Wilderman, P. J., Vasil, A. I., and Vasil, M. L. (2002) Mol. Microbiol. 45, 1277-1287] ensures sufficient concentrations of apo-Bfd to bind BfrB and unlock the iron stored in its core. Although these findings are in contrast to previous speculations suggesting redox mediation of electron transfer by holo-Bfd, the ability of apo-Bfd to promote iron mobilization is an economical strategy used by the cell because it obviates the need to further deplete cellular iron levels to assemble iron-sulfur clusters in Bfd before the iron stored in BfrB can be mobilized and utilized.
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Affiliation(s)
- Saroja K Weeratunga
- Ralph N. Adams Institute for Bioanalytical Chemistry, Department of Chemistry, University of Kansas, Lawrence, Kansas 66047, USA
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Paladini DH, Musumeci MA, Carrillo N, Ceccarelli EA. Induced fit and equilibrium dynamics for high catalytic efficiency in ferredoxin-NADP(H) reductases. Biochemistry 2009; 48:5760-8. [PMID: 19435322 DOI: 10.1021/bi9004232] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ferredoxin-NADP(H) reductase (FNR) is a FAD-containing protein that catalyzes the reversible transfer of electrons between NADP(H) and ferredoxin or flavodoxin. This enzyme participates in the redox-based metabolism of plastids, mitochondria, and bacteria. Plastidic plant-type FNRs are very efficient reductases in supporting photosynthesis. They have a strong preference for NADP(H) over NAD(H), consistent with the main physiological role of NADP(+) photoreduction. In contrast, FNRs from organisms with heterotrophic metabolisms or anoxygenic photosynthesis display turnover rates that are up to 100-fold lower than those of their plastidic and cyanobacterial counterparts. With the aim of elucidating the mechanisms by which plastidic enzymes achieve such high catalytic efficiencies and NADP(H) specificity, we investigated the manner in which the NADP(H) nicotinamide enters and properly binds to the catalytic site. Analyzing the interaction of different nucleotides, substrate analogues, and aromatic compounds with the wild type and the mutant Y308S-FNR from pea, we found that the interaction of the 2'-P-AMP moiety from NADP(+) induces a change that favors the interaction of the nicotinamide, thereby facilitating the catalytic process. Furthermore, the main role of the terminal tyrosine, Y308, is to destabilize the interaction of the nicotinamide with the enzyme, inducing product release and favoring discrimination of the nucleotide substrate. We determined that this function can be replaced by the addition of aromatic compounds that freely diffuse in solution and establish a dynamic equilibrium, reversing the effect of the mutation in the Y308S-FNR mutant.
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Affiliation(s)
- Darío H Paladini
- Molecular Biology Division, Instituto de Biología Molecular y Celular de Rosario (IBR), CONICET, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina
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14
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Beaumont E, Lambry JC, Blanchard-Desce M, Martasek P, Panda SP, van Faassen EEH, Brochon JC, Deprez E, Slama-Schwok A. NO formation by neuronal NO-synthase can be controlled by ultrafast electron injection from a nanotrigger. Chembiochem 2009; 10:690-701. [PMID: 19222033 DOI: 10.1002/cbic.200800721] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Nitric oxide synthases (NOSs) are unique flavohemoproteins with various roles in mammalian physiology. Constitutive NOS catalysis is initiated by fast hydride transfer from NADPH, followed by slower structural rearrangements. We used a photoactive nanotrigger (NT) to study the initial electron transfer to FAD in native neuronal NOS (nNOS) catalysis. Molecular modeling and fluorescence spectroscopy showed that selective NT binding to NADPH sites close to FAD is able to override Phe1395 regulation. Ultrafast injection of electrons into the protein electron pathway by NT photoactivation through the use of a femtosecond laser pulse is thus possible. We show that calmodulin, required for NO synthesis by constitutive NOS, strongly promotes intramolecular electron flow (6.2-fold stimulation) by a mechanism involving proton transfer to the reduced FAD(-) site. Site-directed mutagenesis using the S1176A and S1176T mutants of nNOS supports this hypothesis. The NT synchronized the initiation of flavoenzyme catalysis, leading to the formation of NO, as detected by EPR. This NT is thus promising for time-resolved X-ray and other cellular applications.
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Affiliation(s)
- Edward Beaumont
- Unité INSERM 696, Laboratory for Optics and Biosciences, Ecole Polytechnique, Palaiseau, France
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15
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Alontaga AY, Rodriguez JC, Schönbrunn E, Becker A, Funke T, Yukl ET, Hayashi T, Stobaugh J, Moënne-Loccoz P, Rivera M. Structural characterization of the hemophore HasAp from Pseudomonas aeruginosa: NMR spectroscopy reveals protein-protein interactions between Holo-HasAp and hemoglobin. Biochemistry 2009; 48:96-109. [PMID: 19072037 DOI: 10.1021/bi801860g] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Pseudomonas aeruginosa secretes a 205 residue long hemophore (full-length HasAp) that is subsequently cleaved at the C'-terminal domain to produce mainly a 184 residue long truncated HasAp that scavenges heme [Letoffé, S., Redeker, V., and Wandersman, C. (1998) Mol. Microbiol. 28, 1223-1234]. HasAp has been characterized by X-ray crystallography and in solution by NMR spectroscopy. The X-ray crystal structure of truncated HasAp revealed a polypeptide alphabeta fold and a ferriheme coordinated axially by His32 and Tyr75, with the side chain of His83 poised to accept a hydrogen bond from the Tyr75 phenolic acid group. NMR investigations conducted with full-length HasAp showed that the carboxyl-terminal tail (21 residues) is disordered and conformationally flexible. NMR spectroscopic investigations aimed at studying a complex between apo-HasAp and human methemoglobin were stymied by the rapid heme capture by the hemophore. In an effort to circumvent this problem NMR spectroscopy was used to monitor the titration of 15N-labeled holo-HasAp with hemoglobin. These studies allowed identification of a specific area on the surface of truncated HasAp, encompassing the axial ligand His32 loop that serves as a transient site of interaction with hemoglobin. These findings are discussed in the context of a putative encounter complex between apo-HasAp and hemoglobin that leads to efficient hemoglobin-heme capture by the hemophore. Similar experiments conducted with full-length 15N-labeled HasAp and hemoglobin revealed a transient interaction site in full-length HasAp similar to that observed in the truncated hemophore. The spectral perturbations observed while investigating these interactions, however, are weaker than those observed for the interactions between hemoglobin and truncated HasAp, suggesting that the disordered tail in the full-length HasAp must be proteolyzed in the extracellular milieu to make HasAp a more efficient hemophore.
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Affiliation(s)
- Aileen Y Alontaga
- Ralph N. Adams Institute for Bioanalytical Chemistry and Department of Chemistry, University of Kansas, Lawrence, Kansas 66047, USA
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Bortolotti A, Pérez-Dorado I, Goñi G, Medina M, Hermoso JA, Carrillo N, Cortez N. Coenzyme binding and hydride transfer in Rhodobacter capsulatus ferredoxin/flavodoxin NADP(H) oxidoreductase. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1794:199-210. [PMID: 18973834 DOI: 10.1016/j.bbapap.2008.09.013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2008] [Revised: 09/12/2008] [Accepted: 09/16/2008] [Indexed: 10/21/2022]
Abstract
Ferredoxin-NADP(H) reductases catalyse the reversible hydride/electron exchange between NADP(H) and ferredoxin/flavodoxin, comprising a structurally defined family of flavoenzymes with two distinct subclasses. Those present in Gram-negative bacteria (FPRs) display turnover numbers of 1-5 s(-1) while the homologues of cyanobacteria and plants (FNRs) developed a 100-fold activity increase. We investigated nucleotide interactions and hydride transfer in Rhodobacter capsulatus FPR comparing them to those reported for FNRs. NADP(H) binding proceeds as in FNRs with stacking of the nicotinamide on the flavin, which resulted in formation of charge-transfer complexes prior to hydride exchange. The affinity of FPR for both NADP(H) and 2'-P-AMP was 100-fold lower than that of FNRs. The crystal structure of FPR in complex with 2'-P-AMP and NADP(+) allowed modelling of the adenosine ring system bound to the protein, whereas the nicotinamide portion was either not visible or protruding toward solvent in different obtained crystals. Stabilising contacts with the active site residues are different in the two reductase classes. We conclude that evolution to higher activities in FNRs was partially favoured by modification of NADP(H) binding in the initial complexes through changes in the active site residues involved in stabilisation of the adenosine portion of the nucleotide and in the mobile C-terminus of FPR.
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Affiliation(s)
- Ana Bortolotti
- Instituto de Biología Molecular y Celular de Rosario, Universidad Nacional de Rosario, Suipacha 531, S2002LRK Rosario, Argentina
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