1
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Dali A, Gabler T, Sebastiani F, Furtmüller PG, Becucci M, Hofbauer S, Smulevich G. Entrance channels to coproheme in coproporphyrin ferrochelatase probed by exogenous imidazole binding. J Inorg Biochem 2024; 260:112681. [PMID: 39146673 DOI: 10.1016/j.jinorgbio.2024.112681] [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: 05/17/2024] [Revised: 07/25/2024] [Accepted: 07/27/2024] [Indexed: 08/17/2024]
Abstract
Iron insertion into porphyrins is an essential step in heme biosynthesis. In the coproporphyrin-dependent pathway, specific to monoderm bacteria, this reaction is catalyzed by the monomeric enzyme coproporphyrin ferrochelatase. In addition to the mechanistic details of the metalation of the porphyrin, the identification of the substrate access channel for ferrous iron to the active site is important to fully understand this enzymatic system. In fact, whether the iron reaches the active site from the distal or the proximal porphyrin side is still under debate. In this study we have thoroughly addressed this question in Listeria monocytogenes coproporphyrin ferrochelatase by X-ray crystallography, steady-state and pre-steady-state imidazole ligand binding studies, together with a detailed spectroscopic characterization using resonance Raman and UV-vis absorption spectroscopies in solution. Analysis of the X-ray structures of coproporphyrin ferrochelatase-coproporphyrin III crystals soaked with ferrous iron shows that iron is present on both sides of the porphyrin. The kinetic and spectroscopic study of imidazole binding to coproporphyrin ferrochelatase‑iron coproporphyrin III clearly indicates the presence of two possible binding sites in this monomeric enzyme that influence each other, which is confirmed by the observed cooperativity at steady-state and a biphasic behavior in the pre-steady-state experiments. The current results are discussed in the context of the entire heme biosynthetic pathway and pave the way for future studies focusing on protein-protein interactions.
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Affiliation(s)
- Andrea Dali
- Dipartimento di Chimica "Ugo Schiff" (DICUS), Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy
| | - Thomas Gabler
- BOKU University, Department of Chemistry, Institute of Biochemistry, Muthgasse 18, A-1190 Vienna, Austria
| | - Federico Sebastiani
- Dipartimento di Chimica "Ugo Schiff" (DICUS), Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy
| | - Paul G Furtmüller
- BOKU University, Department of Chemistry, Institute of Biochemistry, Muthgasse 18, A-1190 Vienna, Austria
| | - Maurizio Becucci
- Dipartimento di Chimica "Ugo Schiff" (DICUS), Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy; The European Laboratory for Non-Linear Spectroscopy (LENS), Via Nello Carrara 1, I-50019 Sesto Fiorentino (FI), Italy.
| | - Stefan Hofbauer
- BOKU University, Department of Chemistry, Institute of Biochemistry, Muthgasse 18, A-1190 Vienna, Austria.
| | - Giulietta Smulevich
- Dipartimento di Chimica "Ugo Schiff" (DICUS), Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy; INSTM Research Unit of Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (FI), Italy.
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2
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Dali A, Sebastiani F, Gabler T, Frattini G, Moreno DM, Estrin DA, Becucci M, Hofbauer S, Smulevich G. Proximal ligand tunes active site structure and reactivity in bacterial L. monocytogenes coproheme ferrochelatase. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2024; 313:124120. [PMID: 38479228 DOI: 10.1016/j.saa.2024.124120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 02/21/2024] [Accepted: 03/03/2024] [Indexed: 04/02/2024]
Abstract
Ferrochelatases catalyze the insertion of ferrous iron into the porphyrin during the heme b biosynthesis pathway, which is fundamental for both prokaryotes and eukaryotes. Interestingly, in the active site of ferrochelatases, the proximal ligand coordinating the porphyrin iron of the product is not conserved, and its catalytic role is still unclear. Here we compare the L. monocytogenes bacterial coproporphyrin ferrochelatase native enzyme together with selected variants, where the proximal Tyr residue was replaced by a His (i.e. the most common ligand in heme proteins), a Met or a Phe (as in human and actinobacterial ferrochelatases, respectively), in their Fe(III), Fe(II) and Fe(II)-CO adduct forms. The study of the active site structure and the activity of the proteins in solution has been performed by UV-vis electronic absorption and resonance Raman spectroscopies, biochemical characterization, and classical MD simulations. All the mutations alter the H-bond interactions between the iron porphyrin propionate groups and the protein, and induce effects on the activity, depending on the polarity of the proximal ligand. The overall results confirm that the weak or non-existing coordination of the porphyrin iron by the proximal residue is essential for the binding of the substrate and the release of the final product.
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Affiliation(s)
- Andrea Dali
- Dipartimento di Chimica "Ugo Schiff" (DICUS), Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy
| | - Federico Sebastiani
- Dipartimento di Chimica "Ugo Schiff" (DICUS), Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy
| | - Thomas Gabler
- University of Natural Resources and Life Sciences, Department of Chemistry, Institute of Biochemistry, Muthgasse 18, A-1190 Vienna, Austria
| | - Gianfranco Frattini
- Instituto de Química Rosario (IQUIR, CONICET-UNR) and Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Rosario, Santa Fe, Argentina
| | - Diego M Moreno
- Instituto de Química Rosario (IQUIR, CONICET-UNR) and Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Rosario, Santa Fe, Argentina
| | - Darío A Estrin
- Facultad de Ciencias Exactas y Naturales, Departamento de Química Inorgánica, Analítica y Química Física, Universidad de Buenos Aires, Intendente Güiraldes, 2160 Buenos Aires, Argentina; CONICET - Universidad de Buenos Aires, Instituto de Química-Física de los Materiales, Medio Ambiente y Energía (INQUIMAE), Ciudad Universitaria, Pabellón 2, Buenos Aires, Argentina
| | - Maurizio Becucci
- Dipartimento di Chimica "Ugo Schiff" (DICUS), Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy.
| | - Stefan Hofbauer
- University of Natural Resources and Life Sciences, Department of Chemistry, Institute of Biochemistry, Muthgasse 18, A-1190 Vienna, Austria.
| | - Giulietta Smulevich
- Dipartimento di Chimica "Ugo Schiff" (DICUS), Università di Firenze, Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy; INSTM Research Unit of Firenze, via della Lastruccia 3, I-50019 Sesto Fiorentino, Italy.
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3
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McGuire MR, Espenshade PJ. PGRMC1: An enigmatic heme-binding protein. Pharmacol Ther 2023; 241:108326. [PMID: 36463977 PMCID: PMC9839567 DOI: 10.1016/j.pharmthera.2022.108326] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Revised: 11/22/2022] [Accepted: 11/28/2022] [Indexed: 12/03/2022]
Abstract
Progesterone Receptor Membrane Component 1 (PGRMC1) is a heme-binding protein that has been implicated in a wide range of cell and tissue functions, including cytochromes P450 activity, heme homeostasis, cancer, female reproduction, and protein quality control. Despite an extensive body of literature, a relative lack of mechanistic insight means that how PGRMC1 functions in these different aspects of biology is largely unknown. This review provides an overview of the PGRMC1 literature, highlighting what information is rigorously supported by experimental evidence and where additional investigation is warranted. The central role of PGRMC1 in supporting cytochrome P450 activity is discussed at length. Building on existing models of PGRMC1 function, a speculative model is proposed using the reviewed literature in which PGRMC1 functions as a heme chaperone to shuttle heme from its site of synthesis in the mitochondrion to other subcellular compartments. By spotlighting knowledge gaps, this review will motivate investigators to better understand this enigmatic protein.
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Affiliation(s)
- Meredith R McGuire
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Peter J Espenshade
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Department of Oncology, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Physiology 107B, Baltimore, MD 21205, USA.
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4
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Ghosh P, Vidal C, Dey S, Zhang L. Mitochondria Targeting as an Effective Strategy for Cancer Therapy. Int J Mol Sci 2020; 21:E3363. [PMID: 32397535 PMCID: PMC7247703 DOI: 10.3390/ijms21093363] [Citation(s) in RCA: 118] [Impact Index Per Article: 29.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 04/30/2020] [Accepted: 05/06/2020] [Indexed: 12/14/2022] Open
Abstract
Mitochondria are well known for their role in ATP production and biosynthesis of macromolecules. Importantly, increasing experimental evidence points to the roles of mitochondrial bioenergetics, dynamics, and signaling in tumorigenesis. Recent studies have shown that many types of cancer cells, including metastatic tumor cells, therapy-resistant tumor cells, and cancer stem cells, are reliant on mitochondrial respiration, and upregulate oxidative phosphorylation (OXPHOS) activity to fuel tumorigenesis. Mitochondrial metabolism is crucial for tumor proliferation, tumor survival, and metastasis. Mitochondrial OXPHOS dependency of cancer has been shown to underlie the development of resistance to chemotherapy and radiotherapy. Furthermore, recent studies have demonstrated that elevated heme synthesis and uptake leads to intensified mitochondrial respiration and ATP generation, thereby promoting tumorigenic functions in non-small cell lung cancer (NSCLC) cells. Also, lowering heme uptake/synthesis inhibits mitochondrial OXPHOS and effectively reduces oxygen consumption, thereby inhibiting cancer cell proliferation, migration, and tumor growth in NSCLC. Besides metabolic changes, mitochondrial dynamics such as fission and fusion are also altered in cancer cells. These alterations render mitochondria a vulnerable target for cancer therapy. This review summarizes recent advances in the understanding of mitochondrial alterations in cancer cells that contribute to tumorigenesis and the development of drug resistance. It highlights novel approaches involving mitochondria targeting in cancer therapy.
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Affiliation(s)
| | | | | | - Li Zhang
- Department of Biological Sciences, The University of Texas at Dallas, Richardson, TX 75080, USA; (P.G.); (C.V.); (S.D.)
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5
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Latham RD, Torrado M, Atto B, Walshe JL, Wilson R, Guss JM, Mackay JP, Tristram S, Gell DA. A heme-binding protein produced by Haemophilus haemolyticus inhibits non-typeable Haemophilus influenzae. Mol Microbiol 2019; 113:381-398. [PMID: 31742788 DOI: 10.1111/mmi.14426] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2019] [Revised: 11/14/2019] [Accepted: 11/15/2019] [Indexed: 01/02/2023]
Abstract
Commensal bacteria serve as an important line of defense against colonisation by opportunisitic pathogens, but the underlying molecular mechanisms remain poorly explored. Here, we show that strains of a commensal bacterium, Haemophilus haemolyticus, make hemophilin, a heme-binding protein that inhibits growth of the opportunistic pathogen, non-typeable Haemophilus influenzae (NTHi) in culture. We purified the NTHi-inhibitory protein from H. haemolyticus and identified the hemophilin gene using proteomics and a gene knockout. An x-ray crystal structure of recombinant hemophilin shows that the protein does not belong to any of the known heme-binding protein folds, suggesting that it evolved independently. Biochemical characterisation shows that heme can be captured in the ferrous or ferric state, and with a variety of small heme-ligands bound, suggesting that hemophilin could function under a range of physiological conditions. Hemophilin knockout bacteria show a limited capacity to utilise free heme for growth. Our data suggest that hemophilin is a hemophore and that inhibition of NTHi occurs by heme starvation, raising the possibility that competition from hemophilin-producing H. haemolyticus could antagonise NTHi colonisation in the respiratory tract.
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Affiliation(s)
- Roger D Latham
- School of Medicine, University of Tasmania, Hobart, Australia
| | - Mario Torrado
- School of Life and Environmental Sciences, University of Sydney, Sydney, Australia
| | - Brianna Atto
- School of Health Sciences, University of Tasmania, Launceston, Australia
| | - James L Walshe
- School of Life and Environmental Sciences, University of Sydney, Sydney, Australia
| | - Richard Wilson
- Central Science Laboratory, University of Tasmania, Hobart, Australia
| | - J Mitchell Guss
- School of Life and Environmental Sciences, University of Sydney, Sydney, Australia
| | - Joel P Mackay
- School of Life and Environmental Sciences, University of Sydney, Sydney, Australia
| | - Stephen Tristram
- School of Health Sciences, University of Tasmania, Launceston, Australia
| | - David A Gell
- School of Medicine, University of Tasmania, Hobart, Australia
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6
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Scheidt WR, Li J, Sage JT. What Can Be Learned from Nuclear Resonance Vibrational Spectroscopy: Vibrational Dynamics and Hemes. Chem Rev 2017; 117:12532-12563. [PMID: 28921972 PMCID: PMC5639469 DOI: 10.1021/acs.chemrev.7b00295] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
![]()
Nuclear resonance
vibrational spectroscopy (NRVS; also known as
nuclear inelastic scattering, NIS) is a synchrotron-based method that
reveals the full spectrum of vibrational dynamics for Mössbauer
nuclei. Another major advantage, in addition to its completeness (no
arbitrary optical selection rules), is the unique selectivity of NRVS.
The basics of this recently developed technique are first introduced
with descriptions of the experimental requirements and data analysis
including the details of mode assignments. We discuss the use of NRVS
to probe 57Fe at the center of heme and heme protein derivatives
yielding the vibrational density of states for the iron. The application
to derivatives with diatomic ligands (O2, NO, CO, CN–) shows the strong capabilities of identifying mode
character. The availability of the complete vibrational spectrum of
iron allows the identification of modes not available by other techniques.
This permits the correlation of frequency with other physical properties.
A significant example is the correlation we find between the Fe–Im
stretch in six-coordinate Fe(XO) hemes and the trans Fe–N(Im)
bond distance, not possible previously. NRVS also provides uniquely
quantitative insight into the dynamics of the iron. For example, it
provides a model-independent means of characterizing the strength
of iron coordination. Prediction of the temperature-dependent mean-squared
displacement from NRVS measurements yields a vibrational “baseline”
for Fe dynamics that can be compared with results from techniques
that probe longer time scales to yield quantitative insights into
additional dynamical processes.
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Affiliation(s)
- W Robert Scheidt
- Department of Chemistry and Biochemistry, University of Notre Dame , Notre Dame, Indiana 46556 United States
| | - Jianfeng Li
- College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences , YanQi Lake, HuaiRou District, Beijing 101408, China
| | - J Timothy Sage
- Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University , 120 Forsyth Street, Boston, Massachusetts 02115, United States
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7
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Uchida T, Kobayashi N, Muneta S, Ishimori K. The Iron Chaperone Protein CyaY from Vibrio cholerae Is a Heme-Binding Protein. Biochemistry 2017; 56:2425-2434. [DOI: 10.1021/acs.biochem.6b01304] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Takeshi Uchida
- Department
of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
- Graduate
School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-8628, Japan
| | - Noriyuki Kobayashi
- Graduate
School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-8628, Japan
| | - Souichiro Muneta
- Graduate
School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-8628, Japan
| | - Koichiro Ishimori
- Department
of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
- Graduate
School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-8628, Japan
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8
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Celis AI, Gauss GH, Streit BR, Shisler K, Moraski GC, Rodgers KR, Lukat-Rodgers GS, Peters JW, DuBois JL. Structure-Based Mechanism for Oxidative Decarboxylation Reactions Mediated by Amino Acids and Heme Propionates in Coproheme Decarboxylase (HemQ). J Am Chem Soc 2017; 139:1900-1911. [PMID: 27936663 PMCID: PMC5348300 DOI: 10.1021/jacs.6b11324] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Coproheme decarboxylase catalyzes two sequential oxidative decarboxylations with H2O2 as the oxidant, coproheme III as substrate and cofactor, and heme b as the product. Each reaction breaks a C-C bond and results in net loss of hydride, via steps that are not clear. Solution and solid-state structural characterization of the protein in complex with a substrate analog revealed a highly unconventional H2O2-activating distal environment with the reactive propionic acids (2 and 4) on the opposite side of the porphyrin plane. This suggested that, in contrast to direct C-H bond cleavage catalyzed by a high-valent iron intermediate, the coproheme oxidations must occur through mediating amino acid residues. A tyrosine that hydrogen bonds to propionate 2 in a position analogous to the substrate in ascorbate peroxidase is essential for both decarboxylations, while a lysine that salt bridges to propionate 4 is required solely for the second. A mechanism is proposed in which propionate 2 relays an oxidizing equivalent from a coproheme compound I intermediate to the reactive deprotonated tyrosine, forming Tyr•. This residue then abstracts a net hydrogen atom (H•) from propionate 2, followed by migration of the unpaired propionyl electron to the coproheme iron to yield the ferric harderoheme and CO2 products. A similar pathway is proposed for decarboxylation of propionate 4, but with a lysine residue as an essential proton shuttle. The proposed reaction suggests an extended relay of heme-mediated e-/H+ transfers and a novel route for the conversion of carboxylic acids to alkenes.
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Affiliation(s)
- Arianna I. Celis
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717-3400
| | - George H. Gauss
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717-3400
| | - Bennett R. Streit
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717-3400
| | - Krista Shisler
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717-3400
| | - Garrett C. Moraski
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717-3400
| | - Kenton R. Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050
| | - Gudrun S. Lukat-Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050
| | - John W. Peters
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717-3400
| | - Jennifer L. DuBois
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717-3400
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9
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Uluisik RC, Akbas N, Lukat-Rodgers GS, Adrian SA, Allen CE, Schmitt MP, Rodgers KR, Dixon DW. Characterization of the second conserved domain in the heme uptake protein HtaA from Corynebacterium diphtheriae. J Inorg Biochem 2017; 167:124-133. [PMID: 27974280 PMCID: PMC5199035 DOI: 10.1016/j.jinorgbio.2016.11.027] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Revised: 10/19/2016] [Accepted: 11/22/2016] [Indexed: 11/20/2022]
Abstract
HtaA is a heme-binding protein that is part of the heme uptake system in Corynebacterium diphtheriae. HtaA contains two conserved regions (CR1 and CR2). It has been previously reported that both domains can bind heme; the CR2 domain binds hemoglobin more strongly than the CR1 domain. In this study, we report the biophysical characteristics of HtaA-CR2. UV-visible spectroscopy and resonance Raman experiments are consistent with this domain containing a single heme that is bound to the protein through an axial tyrosine ligand. Mutants of conserved tyrosine and histidine residues (Y361, H412, and Y490) have been studied. These mutants are isolated with very little heme (≤5%) in comparison to the wild-type protein (~20%). Reconstitution after removal of the heme with butanone gave an alternative form of the protein. The HtaA-CR2 fold is very stable; it was necessary to perform thermal denaturation experiments in the presence of guanidinium hydrochloride. HtaA-CR2 unfolds extremely slowly; even in 6.8M GdnHCl at 37°C, the half-life was 5h. In contrast, the apo forms of WT HtaA-CR2 and the aforementioned mutants unfolded at much lower concentrations of GdnHCl, indicating the role of heme in stabilizing the structure and implying that heme transfer is effected only to a partner protein in vivo.
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Affiliation(s)
- Rizvan C Uluisik
- Department of Chemistry, Georgia State University, Atlanta, GA 30302-3965, United States
| | - Neval Akbas
- Department of Chemistry, Georgia State University, Atlanta, GA 30302-3965, United States
| | - Gudrun S Lukat-Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050, United States
| | - Seth A Adrian
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050, United States
| | - Courtni E Allen
- Laboratory of Respiratory and Special Pathogens, Division of Bacterial, Parasitic, and Allergenic Products, Center for Biologics Evaluation, and Research, Food and Drug Administration, Silver Spring, MD 20993, United States
| | - Michael P Schmitt
- Laboratory of Respiratory and Special Pathogens, Division of Bacterial, Parasitic, and Allergenic Products, Center for Biologics Evaluation, and Research, Food and Drug Administration, Silver Spring, MD 20993, United States
| | - Kenton R Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050, United States.
| | - Dabney W Dixon
- Department of Chemistry, Georgia State University, Atlanta, GA 30302-3965, United States.
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10
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Draganova EB, Adrian SA, Lukat-Rodgers GS, Keutcha CS, Schmitt MP, Rodgers KR, Dixon DW. Corynebacterium diphtheriae HmuT: dissecting the roles of conserved residues in heme pocket stabilization. J Biol Inorg Chem 2016; 21:875-86. [PMID: 27561288 DOI: 10.1007/s00775-016-1386-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2016] [Accepted: 08/10/2016] [Indexed: 12/30/2022]
Abstract
The heme-binding protein HmuT is part of the Corynebacterium diphtheriae heme uptake pathway and is responsible for the delivery of heme to the HmuUV ABC transporter. HmuT binds heme with a conserved His/Tyr heme axial ligation motif. Sequence alignment revealed additional conserved residues of potential importance for heme binding: R237, Y272 and M292. In this study, site-directed mutations at these three positions provided insight into the nature of axial heme binding to the protein and its effect on the thermal stability of the heme-loaded protein fold. UV-visible absorbance, resonance Raman (rR) and thermal unfolding experiments, along with collision-induced dissociation electrospray ionization mass spectrometry, were used to probe the contributions of each mutated residue to the stability of ϖ HmuT. Thermal unfolding and rR experiments revealed that R237 and M292 are important residues for heme binding. Arginine 237 is a hydrogen-bond donor to the phenol side chain of Y235, which serves as an axial heme ligand. Methionine 292 serves a supporting structural role, favoring the R237 hydrogen-bond donation, which elicits a, heretofore, unobserved modulating influence on π donation by the axial tyrosine ligand in the heme carbonyl complex, HmuT-CO.
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Affiliation(s)
| | - Seth A Adrian
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND, 58108-6050, USA
| | - Gudrun S Lukat-Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND, 58108-6050, USA
| | - Cyrianne S Keutcha
- Department of Chemistry, Georgia State University, Atlanta, GA, 30302-3965, USA
| | - Michael P Schmitt
- Laboratory of Respiratory and Special Pathogens, Division of Bacterial, Parasitic, and Allergenic Products, Center for Biologics Evaluation, and Research, Food and Drug Administration, Silver Spring, MD, 20993, USA
| | - Kenton R Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND, 58108-6050, USA
| | - Dabney W Dixon
- Department of Chemistry, Georgia State University, Atlanta, GA, 30302-3965, USA.
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11
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Sekine Y, Tanzawa T, Tanaka Y, Ishimori K, Uchida T. Cytoplasmic Heme-Binding Protein (HutX) from Vibrio cholerae Is an Intracellular Heme Transport Protein for the Heme-Degrading Enzyme, HutZ. Biochemistry 2016; 55:884-93. [DOI: 10.1021/acs.biochem.5b01273] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yukari Sekine
- Graduate
School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-0810, Japan
| | - Takehito Tanzawa
- Graduate
School of Life Science, Hokkaido University, Sapporo 060-0810, Japan
| | - Yoshikazu Tanaka
- Faculty
of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan
- PRESTO, Japan Science and Technology Agency, Sapporo 060-0810, Japan
| | - Koichiro Ishimori
- Graduate
School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-0810, Japan
- Department
of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
| | - Takeshi Uchida
- Graduate
School of Chemical Sciences and Engineering, Hokkaido University, Sapporo 060-0810, Japan
- Department
of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
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12
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Bennett EH, Akbas N, Adrian SA, Lukat-Rodgers GS, Collins DP, Dawson JH, Allen CE, Schmitt MP, Rodgers KR, Dixon DW. Heme Binding by Corynebacterium diphtheriae HmuT: Function and Heme Environment. Biochemistry 2015; 54:6598-609. [PMID: 26478504 PMCID: PMC4943319 DOI: 10.1021/acs.biochem.5b00666] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The heme uptake pathway (hmu) of Corynebacterium diphtheriae utilizes multiple proteins to bind and transport heme into the cell. One of these proteins, HmuT, delivers heme to the ABC transporter HmuUV. In this study, the axial ligation of the heme in ferric HmuT is probed by examination of wild-type (WT) HmuT and a series of conserved heme pocket residue mutants, H136A, Y235A, and M292A. Characterization by UV-visible, resonance Raman, and magnetic circular dichroism spectroscopies indicates that H136 and Y235 are the axial ligands in ferric HmuT. Consistent with this assignment of axial ligands, ferric WT and H136A HmuT are difficult to reduce while Y235A is reduced readily in the presence of dithionite. The FeCO Raman shifts in WT, H136A, and Y235A HmuT-CO complexes provide further evidence of the axial ligand assignments. Additionally, these frequencies provide insight into the nonbonding environment of the heme pocket. Ferrous Y235A and the Y235A-CO complex reveal that the imidazole of H136 exists in two forms, one neutral and one with imidazolate character, consistent with a hydrogen bond acceptor on the H136 side of the heme. The ferric fluoride complex of Y235A reveals the presence of at least one hydrogen bond donor on the Y235 side of the heme. Hemoglobin utilization assays showed that the axial Y235 ligand is required for heme uptake in HmuT.
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Affiliation(s)
| | - Neval Akbas
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-3965
| | - Seth A. Adrian
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108-6050
| | - Gudrun S. Lukat-Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108-6050
| | - Daniel P. Collins
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208
| | - John H. Dawson
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208
| | - Courtni E. Allen
- Laboratory of Respiratory and Special Pathogens, Division of Bacterial, Parasitic, and Allergenic Products, Center for Biologics Evaluation, and Research, Food and Drug Administration, Silver Spring, Maryland 20993
| | - Michael P. Schmitt
- Laboratory of Respiratory and Special Pathogens, Division of Bacterial, Parasitic, and Allergenic Products, Center for Biologics Evaluation, and Research, Food and Drug Administration, Silver Spring, Maryland 20993
| | - Kenton R. Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108-6050
| | - Dabney W. Dixon
- Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-3965
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13
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Kaluka D, Batabyal D, Chiang BY, Poulos TL, Yeh SR. Spectroscopic and mutagenesis studies of human PGRMC1. Biochemistry 2015; 54:1638-47. [PMID: 25675345 DOI: 10.1021/bi501177e] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Progesterone receptor membrane component 1 (PGRMC1) is a 25 kDa protein with an N-terminal transmembrane domain and a putative C-terminal cytochrome b5 domain. Heme-binding activity of PGRMC1 has been shown in various homologues of PGRMC1. Although the general definition of PGRMC1 is as a progesterone receptor, progesterone-binding activity has not been directly demonstrated in any of the purified PGRMC1 proteins fully loaded with heme. Here, we show that the human homologue of PGRMC1 (hPGRMC1) binds heme in a five-coordinate (5C) high-spin (HS) configuration, with an axial tyrosinate ligand, likely Y95. The negatively charged tyrosinate ligand leads to a relatively low redox potential of approximately -331 mV. The Y95C or Y95F mutation dramatically reduces the ability of the protein to bind heme, supporting the assignment of the axial heme ligand to Y95. On the other hand, the Y95H mutation retains ∼90% of the heme-binding activity. The heme in Y95H is also 5CHS, but it has a hydroxide axial ligand, conceivably stabilized by the engineered-in H95 via an H-bond; CO binding to the distal ligand-binding site leads to an exchange of the axial ligand to a histidine, possibly H95. We show that progesterone binds to hPGRMC1 and introduces spectral changes that manifest conformational changes to the heme. Our data offer the first direct evidence supporting progesterone-binding activity of PGRMC1.
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Affiliation(s)
- Daniel Kaluka
- Department of Physiology and Biophysics, Albert Einstein College of Medicine , 1300 Morris Park Avenue, Bronx, New York 10461, United States
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14
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Ozaki SI, Sato T, Sekine Y, Migita CT, Uchida T, Ishimori K. Spectroscopic studies on HasA from Yersinia pseudotuberculosis. J Inorg Biochem 2014; 138:31-38. [DOI: 10.1016/j.jinorgbio.2014.04.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 04/21/2014] [Accepted: 04/21/2014] [Indexed: 10/25/2022]
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15
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Linder D, Silvernail NJ, Barabanschikov A, Zhao J, Alp EE, Sturhahn W, Sage JT, Scheidt WR, Rodgers KR. The diagnostic vibrational signature of pentacoordination in heme carbonyls. J Am Chem Soc 2014; 136:9818-21. [PMID: 24950373 PMCID: PMC4120987 DOI: 10.1021/ja503191z] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Indexed: 11/28/2022]
Abstract
Heme-carbonyl complexes are widely exploited for the insight they provide into the structural basis of function in heme-based proteins, by revealing the nature of their bonded and nonbonded interactions with the protein. This report presents two novel results which clearly establish a FeCO vibrational signature for crystallographically verified pentacoordination. First, anisotropy in the NRVS density of states for ν(Fe-C) and δ(FeCO) in oriented single crystals of [Fe(OEP)(CO)] clearly reveals that the Fe-C stretch occurs at higher frequency than the FeCO bend and considerably higher than any previously reported heme carbonyl. Second, DFT calculations on a series of heme carbonyls reveal that the frequency crossover occurs near the weak trans O atom donor, furan. As ν(Fe-C) occurs at lower frequencies than δ(FeCO) in all heme protein carbonyls reported to date, the results reported herein suggest that they are all hexacoordinate.
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Affiliation(s)
- Douglas
P. Linder
- Department
of Chemistry and Biochemistry, North Dakota
State University, Fargo, North Dakota 58105, United States
| | - Nathan J. Silvernail
- Department
of Chemistry and Biochemistry, University
of Notre Dame, Notre Dame, Indiana 46556, United States
| | | | - Jiyong Zhao
- Advanced
Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - E. Ercan Alp
- Advanced
Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Wolfgang Sturhahn
- Advanced
Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - J. Timothy Sage
- Department
of Physics, Northeastern University, Boston, Massachusetts 02115, United States
| | - W. Robert Scheidt
- Department
of Chemistry and Biochemistry, University
of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Kenton R. Rodgers
- Department
of Chemistry and Biochemistry, North Dakota
State University, Fargo, North Dakota 58105, United States
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16
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Mokry DZ, Nadia-Albete A, Johnson MK, Lukat-Rodgers GS, Rodgers KR, Lanzilotta WN. Spectroscopic evidence for a 5-coordinate oxygenic ligated high spin ferric heme moiety in the Neisseria meningitidis hemoglobin binding receptor. Biochim Biophys Acta Gen Subj 2014; 1840:3058-66. [PMID: 24968987 DOI: 10.1016/j.bbagen.2014.06.009] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Revised: 06/13/2014] [Accepted: 06/16/2014] [Indexed: 01/04/2023]
Abstract
BACKGROUND For many pathogenic microorganisms, iron acquisition represents a significant stress during the colonization of a mammalian host. Heme is the single most abundant source of soluble iron in this environment. While the importance of iron assimilation for nearly all organisms is clear, the mechanisms by which heme is acquired and utilized by many bacterial pathogens, even those most commonly found at sites of infection, remain poorly understood. METHODS An alternative protocol for the production and purification of the outer membrane hemoglobin receptor (HmbR) from the pathogen Neisseria meningitidis has facilitated a biophysical characterization of this outer membrane transporter by electronic absorption, circular dichroism, electron paramagnetic resonance, and resonance Raman techniques. RESULTS HmbR co-purifies with 5-coordinate high spin ferric heme bound. The heme binding site accommodates exogenous imidazole as a sixth ligand, which results in a 6-coordinate, low-spin ferric species. Both the 5- and 6-coordinate complexes are reduced by sodium hydrosulfite. Four HmbR variants with a modest decrease in binding efficiency for heme have been identified (H87C, H280A, Y282A, and Y456C). These findings are consistent with an emerging paradigm wherein the ferric iron center of bound heme is coordinated by a tyrosine ligand. CONCLUSION In summary, this study provides the first spectroscopic characterization for any heme or iron transporter in Neisseria meningitidis, and suggests a coordination environment heretofore unobserved in a TonB-dependent hemin transporter. GENERAL SIGNIFICANCE A detailed understanding of the nutrient acquisition pathways in common pathogens such as N. meningitidis provides a foundation for new antimicrobial strategies.
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Affiliation(s)
- David Z Mokry
- Department of Biochemistry & Molecular Biology, University of Georgia, Athens, GA 30602, USA
| | | | - Michael K Johnson
- Department of Chemistry, University of Georgia, Athens, GA 30602, USA
| | - Gudrun S Lukat-Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050, USA
| | - Kenton R Rodgers
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050, USA
| | - William N Lanzilotta
- Department of Biochemistry & Molecular Biology, University of Georgia, Athens, GA 30602, USA.
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17
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González-López MA, Velázquez-Guadarrama N, Romero-Espejel ME, Olivares-Trejo JDJ. Helicobacter pylori secretes the chaperonin GroEL (HSP60), which binds iron. FEBS Lett 2013; 587:1823-8. [PMID: 23684642 DOI: 10.1016/j.febslet.2013.04.048] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Revised: 04/06/2013] [Accepted: 04/26/2013] [Indexed: 12/16/2022]
Abstract
Helicobacter pylori is a bacterium that can use multiple iron sources. However, it is unknown whether this bacterium secretes molecules such as siderophores or haemophores to scavenge iron. Here, we report the first secreted iron-binding protein of H. pylori, which we purified by haem-affinity chromatography. Mass spectrometry analysis revealed its identity as chaperonin (HpGroEL). When we compared HpGroEL with EcGroEL from Escherichia coli, they were homologous, showing 60% similarity. Additionally, purified cytoplasmic HpGroEL could also bind iron. Perhaps H. pylori secretes HpGroEL to maintain the appropriate folding of extracellular proteins and to bind iron.
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Affiliation(s)
- Marco Antonio González-López
- Posgrado en Ciencias Genómicas, Universidad Autónoma de la Ciudad de México, San Lorenzo 290, Col Del Valle, México DF, Mexico
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18
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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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19
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Hannibal L, Collins D, Brassard J, Chakravarti R, Vempati R, Dorlet P, Santolini J, Dawson JH, Stuehr DJ. Heme binding properties of glyceraldehyde-3-phosphate dehydrogenase. Biochemistry 2012; 51:8514-29. [PMID: 22957700 DOI: 10.1021/bi300863a] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a glycolytic enzyme that also functions in transcriptional regulation, oxidative stress, vesicular trafficking, and apoptosis. Because GAPDH is required for the insertion of cellular heme into inducible nitric oxide synthase [Chakravarti, R., et al. (2010) Proc. Natl. Acad. Sci. U.S.A. 107, 18004-18009], we extensively characterized the heme binding properties of GAPDH. Substoichiometric amounts of ferric heme bound to GAPDH (one heme per GAPDH tetramer) to form a low-spin complex with UV-visible maxima at 362, 418, and 537 nm and when reduced to ferrous gave maxima at 424, 527, and 559 nm. Ferric heme association and dissociation rate constants at 10 °C were as follows: k(on) = 17800 M(-1) s(-1), k(off1) = 7.0 × 10(-3) s(-1), and k(off2) = 3.3 × 10(-4) s(-1) (giving approximate affinities of 19-390 nM). Ferrous heme bound more poorly to GAPDH and dissociated with a k(off) of 4.2 × 10(-3) s(-1). Magnetic circular dichroism, resonance Raman, and electron paramagnetic resonance spectroscopic data on the ferric, ferrous, and ferrous-CO complexes of GAPDH showed that the heme is bis-ligated with His as the proximal ligand. The distal ligand in the ferric complex was not displaced by CN(-) or N(3)(-) but in the ferrous complex could be displaced by CO at a rate of 1.75 s(-1) (for >0.2 mM CO). Studies with heme analogues revealed selectivity toward the coordinating metal and porphyrin ring structure. The GAPDH-heme complex was isolated from bacteria induced to express rabbit GAPDH in the presence of δ-aminolevulinic acid. Our finding of heme binding to GAPDH expands the protein's potential roles. The strength, selectivity, reversibility, and redox sensitivity of heme binding to GAPDH are consistent with it performing heme sensing or heme chaperone-like functions in cells.
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Affiliation(s)
- Luciana Hannibal
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
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20
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Caillet-Saguy C, Piccioli M, Turano P, Lukat-Rodgers G, Wolff N, Rodgers KR, Izadi-Pruneyre N, Delepierre M, Lecroisey A. Role of the iron axial ligands of heme carrier HasA in heme uptake and release. J Biol Chem 2012; 287:26932-43. [PMID: 22700962 DOI: 10.1074/jbc.m112.366385] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The hemophore protein HasA from Serratia marcescens cycles between two states as follows: the heme-bound holoprotein, which functions as a carrier of the metal cofactor toward the membrane receptor HasR, and the heme-free apoprotein fishing for new porphyrin to be taken up after the heme has been delivered to HasR. Holo- and apo-forms differ for the conformation of the two loops L1 and L2, which provide the axial ligands of the iron through His(32) and Tyr(75), respectively. In the apo-form, loop L1 protrudes toward the solvent far away from loop L2; in the holoprotein, closing of the loops on the heme occurs upon establishment of the two axial coordination bonds. We have established that the two variants obtained via single point mutations of either axial ligand (namely H32A and Y75A) are both in the closed conformation. The presence of the heme and one out of two axial ligands is sufficient to establish a link between L1 and L2, thanks to the presence of coordinating solvent molecules. The latter are stabilized in the iron coordination environment by H-bond interactions with surrounding protein residues. The presence of such a water molecule in both variants is revealed here through a set of different spectroscopic techniques. Previous studies had shown that heme release and uptake processes occur via intermediate states characterized by a Tyr(75)-iron-bound form with open conformation of loop L1. Here, we demonstrate that these states do not naturally occur in the free protein but can only be driven by the interaction with the partner proteins.
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Affiliation(s)
- Célia Caillet-Saguy
- Unité de RMN des Biomolecules (CNRS URA 2185), Institut Pasteur, 28 Rue du Docteur Roux, 75015 Paris, France.
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21
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Owens CP, Du J, Dawson JH, Goulding CW. Characterization of heme ligation properties of Rv0203, a secreted heme binding protein involved in Mycobacterium tuberculosis heme uptake. Biochemistry 2012; 51:1518-31. [PMID: 22283334 DOI: 10.1021/bi2018305] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
The secreted Mycobacterium tuberculosis (Mtb) heme binding protein Rv0203 has been shown to play a role in Mtb heme uptake. In this work, we use spectroscopic (absorption, electron paramagnetic resonance, and magnetic circular dichrosim) methods to further characterize the heme coordination environments of His-tagged and native protein forms, Rv0203-His and Rv0203-notag, respectively. Rv0203-His binds the heme molecule through bis-His coordination and is low-spin in both ferric and ferrous oxidation states. Rv0203-notag is high-spin in both oxidation states and shares spectroscopic similarity with pentacoordinate oxygen-ligated heme proteins. Mutagenesis experiments determined that residues Tyr59, His63, and His89 are required for Rv0203-notag to efficiently bind heme, reinforcing the hypothesis based on our previous structural and mutagenesis studies of Rv0203-His. While Tyr59, His63, and His89 are required for the binding of heme to Rv0203-notag, comparison of the absorption spectra of the Rv0203-notag mutants suggests the heme ligand may be the hydroxyl group of Tyr59, although an exogenous hydroxide cannot be ruled out. Additionally, we measured the heme affinities of Rv0203-His and Rv0203-notag using stopped flow techniques. The rates for binding of heme to Rv0203-His and Rv0203-notag are similar, 115 and 133 μM(-1) s(-1), respectively. However, the heme off rates differ quite dramatically, whereby Rv0203-His gives biphasic dissociation kinetics with fast and slow rates of 0.0019 and 0.0002 s(-1), respectively, and Rv0203-notag has a single off rate of 0.082 s(-1). The spectral and heme binding affinity differences between Rv0203-His and Rv0203-notag suggest that the His tag interferes with heme binding. Furthermore, these results imply that the His tag has the ability to stabilize heme binding as well as alter heme ligand coordination of Rv0203 by providing an unnatural histidine ligand. Moreover, the heme affinity of Rv0203-notag is comparable to that of other heme transport proteins, implying that Rv0203 may act as an extracellular heme transporter.
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Affiliation(s)
- Cedric P Owens
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California 92697, United States
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22
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San Francisco B, Bretsnyder EC, Rodgers KR, Kranz RG. Heme ligand identification and redox properties of the cytochrome c synthetase, CcmF. Biochemistry 2011; 50:10974-85. [PMID: 22066495 DOI: 10.1021/bi201508t] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Cytochrome c maturation in many bacteria, archaea, and plant mitochondria involves the integral membrane protein CcmF, which is thought to function as a cytochrome c synthetase by facilitating the final covalent attachment of heme to the apocytochrome c. We previously reported that the E. coli CcmF protein contains a b-type heme that is stably and stoichiometrically associated with the protein and is not the heme attached to apocytochrome c. Here, we show that mutation of either of two conserved transmembrane histidines (His261 or His491) impairs stoichiometric b-heme binding in CcmF and results in spectral perturbations in the remaining heme. Exogeneous imidazole is able to correct cytochrome c maturation for His261 and His491 substitutions with small side chains (Ala or Gly), suggesting that a "cavity" is formed in these CcmF mutants in which imidazole binds and acts as a functional ligand to the b-heme. The results of resonance Raman spectroscopy on wild-type CcmF are consistent with a hexacoordinate low-spin b-heme with at least one endogeneous axial His ligand. Analysis of purified recombinant CcmF proteins from diverse prokaryotes reveals that the b-heme in CcmF is widely conserved. We have also determined the reduction potential of the CcmF b-heme (E(m,7) = -147 mV). We discuss these results in the context of CcmF structure and functions as a heme reductase and cytochrome c synthetase.
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Affiliation(s)
- Brian San Francisco
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri 63130, United States
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23
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Coordination modes of tyrosinate-ligated catalase-type heme enzymes: magnetic circular dichroism studies of Plexaura homomalla allene oxide synthase, Mycobacterium avium ssp. paratuberculosis protein-2744c, and bovine liver catalase in their ferric and ferrous states. J Inorg Biochem 2011; 105:1786-94. [PMID: 22104301 DOI: 10.1016/j.jinorgbio.2011.09.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Revised: 09/15/2011] [Accepted: 09/15/2011] [Indexed: 11/20/2022]
Abstract
Bovine liver catalase (BLC), catalase-related allene oxide synthase (cAOS) from Plexaura homomalla, and a recently isolated protein from the cattle pathogen Mycobacterium avium ssp. paratuberculosis (MAP-2744c (MAP)) are all tyrosinate-ligated heme enzymes whose crystal structures have been reported. cAOS and MAP have low (<20%) sequence similarity to, and significantly different catalytic functions from, BLC. cAOS transforms 8R-hydroperoxy-eicosatetraenoic acid to an allene epoxide, whereas the MAP protein is a putative organic peroxide-dependent peroxidase. To elucidate factors influencing the functions of these and related heme proteins, we have investigated the heme iron coordination properties of these tyrosinate-ligated heme enzymes in their ferric and ferrous states using magnetic circular dichroism and UV-visible absorption spectroscopy. The MAP protein shows remarkable spectral similarities to cAOS and BLC in its native Fe(III) state, but clear differences from ferric proximal heme ligand His93Tyr Mb (myoglobin) mutant, which may be attributed to the presence of an Arg(+)-N(ω)-H···¯O-Tyr (proximal heme axial ligand) hydrogen bond in the first three heme proteins. Furthermore, the spectra of Fe(III)-CN¯, Fe(III)-NO, Fe(II)-NO (except for five-coordinate MAP), Fe(II)-CO, and Fe(II)-O(2) states of cAOS and MAP, but not H93Y Mb, are also similar to the corresponding six-coordinate complexes of BLC, suggesting that a tyrosinate (Tyr-O¯) is the heme axial ligand trans to the bound ligands in these complexes. The Arg(+)-N(ω)-H to ¯O-Tyr hydrogen bond would be expected to modulate the donor properties of the proximal tyrosinate oxyanion and, combined with the subtle differences in the catalytic site structures, affect the activities of cAOS, MAP and BLC.
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24
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Evidence for pH-dependent multiple conformers in iron(II) heme–human serum albumin: spectroscopic and kinetic investigation of carbon monoxide binding. J Biol Inorg Chem 2011; 17:133-47. [DOI: 10.1007/s00775-011-0837-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2011] [Accepted: 08/07/2011] [Indexed: 12/22/2022]
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25
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Mayfield JA, Dehner CA, DuBois JL. Recent advances in bacterial heme protein biochemistry. Curr Opin Chem Biol 2011; 15:260-6. [PMID: 21339081 DOI: 10.1016/j.cbpa.2011.02.002] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2010] [Accepted: 02/01/2011] [Indexed: 01/01/2023]
Abstract
Recent progress in genetics, fed by the burst in genome sequence data, has led to the identification of a host of novel bacterial heme proteins that are now being characterized in structural and mechanistic terms. The following short review highlights very recent work with bacterial heme proteins involved in the uptake, biosynthesis, degradation, and use of heme in respiration and sensing.
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Affiliation(s)
- Jeffery A Mayfield
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
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26
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Molecular basis for the inability of an oxygen atom donor ligand to replace the natural sulfur donor heme axial ligand in cytochrome P450 catalysis. Spectroscopic characterization of the Cys436Ser CYP2B4 mutant. Arch Biochem Biophys 2010; 507:119-25. [PMID: 21147058 DOI: 10.1016/j.abb.2010.12.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2010] [Revised: 12/06/2010] [Accepted: 12/07/2010] [Indexed: 11/21/2022]
Abstract
All cytochrome P450s (CYPs) contain a cysteinate heme iron proximal ligand that plays a crucial role in their mechanism of action. Conversion of the proximal Cys436 to Ser in NH(2)-truncated microsomal CYP2B4 (ΔCYP2B4) transforms the enzyme into a two-electron NADPH oxidase producing H(2)O(2) without monooxygenase activity [K.P. Vatsis, H.M. Peng, M.J. Coon, J. Inorg. Biochem. 91 (2002) 542-553]. To examine the effects of this ligation change on the heme iron spin-state and coordination structure of ΔC436S CYP2B4, the magnetic circular dichroism and electronic absorption spectra of several oxidation/ligation states of the variant have been measured and compared with those of structurally defined heme complexes. The spectra of the substrate-free ferric mutant are indicative of a high-spin five-coordinate structure ligated by anionic serinate. The spectroscopic properties of the dithionite-reduced (deoxyferrous) protein are those of a five-coordinate (high-spin) state, and it is concluded that the proximal ligand has been protonated to yield neutral serine (ROH-donor). Low-spin six-coordinate ferrous complexes of the mutant with neutral sixth ligands (NO, CO, and O(2)) examined are also likely ligated by neutral serine, as would be expected for ferric complexes with anionic sixth ligands such as the hydroperoxo-ferric catalytic intermediate. Ligation of the heme iron by neutral serine vs. deprotonated cysteine is likely the result of the large difference in their acidity. Thus, without the necessary proximal ligand push of the cysteinate, although the ΔC436S mutant can accept two electrons and two protons, it is unable to heterolytically cleave the O-O bond of the hydroperoxo-ferric species to generate Compound I and hydroxylate the substrate.
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27
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Yukl ET, Jepkorir G, Alontaga AY, Pautsch L, Rodriguez JC, Rivera M, Moënne-Loccoz P. Kinetic and spectroscopic studies of hemin acquisition in the hemophore HasAp from Pseudomonas aeruginosa. Biochemistry 2010; 49:6646-54. [PMID: 20586423 DOI: 10.1021/bi100692f] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The extreme limitation of free iron has driven various pathogens to acquire iron from the host in the form of heme. Specifically, several Gram-negative pathogens secrete a heme binding protein known as HasA to scavenge heme from the extracellular environment and to transfer it to the receptor protein HasR for import into the bacterial cell. Structures of heme-bound and apo-HasA homologues show that the heme iron(III) ligands, His32 and Tyr75, reside on loops extending from the core of the protein and that a significant conformational change must occur at the His32 loop upon heme binding. Here, we investigate the kinetics of heme acquisition by HasA from Pseudomonas aeruginosa (HasAp). The rate of heme acquisition from human met-hemoglobin (met-Hb) closely matches that of heme dissociation which suggests a passive mode of heme uptake from this source. The binding of free hemin is characterized by an initial rapid phase forming an intermediate before further conversion to the final complex. Analysis of this same reaction using an H32A variant lacking the His heme ligand shows only the rapid phase to form a heme-protein complex spectroscopically equivalent to that of the wild-type intermediate. Further characterization of these reactions using electron paramagnetic resonance and resonance Raman spectroscopy of rapid freeze quench samples provides support for a model in which heme is initially bound by the Tyr75 to form a high-spin heme-protein complex before slower coordination of the His32 ligand upon closing of the His loop over the heme. The slow rate of this loop closure implies that the induced-fit mechanism of heme uptake in HasAp is not based on a rapid sampling of the H32 loop between open and closed configurations but, rather, that the H32 loop motions are triggered by the formation of the high-spin heme-HasAp intermediate complex.
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Affiliation(s)
- Erik T Yukl
- Department of Science and Engineering, School of Medicine, Oregon Health and Science University, 20000 Northwest Walker Road, Beaverton, Oregon 97006-8921, USA
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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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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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Nicoletti FP, Howes BD, Fittipaldi M, Fanali G, Fasano M, Ascenzi P, Smulevich G. Ibuprofen Induces an Allosteric Conformational Transition in the Heme Complex of Human Serum Albumin with Significant Effects on Heme Ligation. J Am Chem Soc 2008; 130:11677-88. [DOI: 10.1021/ja800966t] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Francesco P. Nicoletti
- Dipartimento di Chimica and INSTM, Università di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (FI), Italy, Dipartimento di Biologia Strutturale e Funzionale, and Centro di Neuroscienze, Università dell’Insubria, Via Alberto da Giussano 12, I-21052 Busto Arsizio (VA), Italy, Centro Interdipartimentale di Microscopia Elettronica, Università Roma Tre, Via della Vasca Navale 79, I-00146 Roma, Italy, and Istituto Nazionale per le Malattie Infettive I.R.C.C.S. ‘Lazzaro Spallanzani’, Via Portuense
| | - Barry D. Howes
- Dipartimento di Chimica and INSTM, Università di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (FI), Italy, Dipartimento di Biologia Strutturale e Funzionale, and Centro di Neuroscienze, Università dell’Insubria, Via Alberto da Giussano 12, I-21052 Busto Arsizio (VA), Italy, Centro Interdipartimentale di Microscopia Elettronica, Università Roma Tre, Via della Vasca Navale 79, I-00146 Roma, Italy, and Istituto Nazionale per le Malattie Infettive I.R.C.C.S. ‘Lazzaro Spallanzani’, Via Portuense
| | - Maria Fittipaldi
- Dipartimento di Chimica and INSTM, Università di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (FI), Italy, Dipartimento di Biologia Strutturale e Funzionale, and Centro di Neuroscienze, Università dell’Insubria, Via Alberto da Giussano 12, I-21052 Busto Arsizio (VA), Italy, Centro Interdipartimentale di Microscopia Elettronica, Università Roma Tre, Via della Vasca Navale 79, I-00146 Roma, Italy, and Istituto Nazionale per le Malattie Infettive I.R.C.C.S. ‘Lazzaro Spallanzani’, Via Portuense
| | - Gabriella Fanali
- Dipartimento di Chimica and INSTM, Università di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (FI), Italy, Dipartimento di Biologia Strutturale e Funzionale, and Centro di Neuroscienze, Università dell’Insubria, Via Alberto da Giussano 12, I-21052 Busto Arsizio (VA), Italy, Centro Interdipartimentale di Microscopia Elettronica, Università Roma Tre, Via della Vasca Navale 79, I-00146 Roma, Italy, and Istituto Nazionale per le Malattie Infettive I.R.C.C.S. ‘Lazzaro Spallanzani’, Via Portuense
| | - Mauro Fasano
- Dipartimento di Chimica and INSTM, Università di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (FI), Italy, Dipartimento di Biologia Strutturale e Funzionale, and Centro di Neuroscienze, Università dell’Insubria, Via Alberto da Giussano 12, I-21052 Busto Arsizio (VA), Italy, Centro Interdipartimentale di Microscopia Elettronica, Università Roma Tre, Via della Vasca Navale 79, I-00146 Roma, Italy, and Istituto Nazionale per le Malattie Infettive I.R.C.C.S. ‘Lazzaro Spallanzani’, Via Portuense
| | - Paolo Ascenzi
- Dipartimento di Chimica and INSTM, Università di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (FI), Italy, Dipartimento di Biologia Strutturale e Funzionale, and Centro di Neuroscienze, Università dell’Insubria, Via Alberto da Giussano 12, I-21052 Busto Arsizio (VA), Italy, Centro Interdipartimentale di Microscopia Elettronica, Università Roma Tre, Via della Vasca Navale 79, I-00146 Roma, Italy, and Istituto Nazionale per le Malattie Infettive I.R.C.C.S. ‘Lazzaro Spallanzani’, Via Portuense
| | - Giulietta Smulevich
- Dipartimento di Chimica and INSTM, Università di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (FI), Italy, Dipartimento di Biologia Strutturale e Funzionale, and Centro di Neuroscienze, Università dell’Insubria, Via Alberto da Giussano 12, I-21052 Busto Arsizio (VA), Italy, Centro Interdipartimentale di Microscopia Elettronica, Università Roma Tre, Via della Vasca Navale 79, I-00146 Roma, Italy, and Istituto Nazionale per le Malattie Infettive I.R.C.C.S. ‘Lazzaro Spallanzani’, Via Portuense
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Kitanishi K, Igarashi J, Hayasaka K, Hikage N, Saiful I, Yamauchi S, Uchida T, Ishimori K, Shimizu T. Heme-binding characteristics of the isolated PAS-A domain of mouse Per2, a transcriptional regulatory factor associated with circadian rhythms. Biochemistry 2008; 47:6157-68. [PMID: 18479150 DOI: 10.1021/bi7023892] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Neuronal PAS protein 2 (NPAS2), a heme-binding transcriptional regulatory factor, is involved in circadian rhythms. Period homologue (Per) is another important transcriptional regulatory factor that binds to cryptochrome (Cry). The resultant Per/Cry heterodimer interacts with the NPAS2/BMAL1 heterodimer to inhibit the transcription of Per and Cry. Previous cell biology experiments indicate that mouse Per2 (mPer2) is also a heme-binding protein, and heme shuttling between mPer2 and NPAS2 may regulate transcription. In the present study, we show that the isolated PAS-A domain of mPer2 (PAS-A-mPer2) binds the Fe(III) protoporphyrin IX complex (hemin) with a heme:protein stoichiometry of 1:1. Optical absorption and EPR spectroscopic findings suggest that the Fe(III)-bound PAS-A-mPer2 is a six-coordinated low-spin complex with Cys and an unknown axial ligand. A Hg (2+) binding study supports the theory that Cys is one of the axial ligands for Fe(III)-bound PAS-A-mPer2. The dissociation rate constant of the Fe(III) complex from PAS-A-mPer2 (6.3 x 10 (-4) s (-1)) was comparable to that of the heme-regulated inhibitor (HRI), a heme-sensor enzyme (1.5 x 10 (-3) s (-1)), but markedly higher than that of metmyoglobin (8.4 x 10 (-7) s (-1)). As confirmed by a Soret absorption spectral shift, heme transferred from the holo basic helix-loop-helix PAS-A of NPAS2 to apoPAS-A-mPer2. The Soret CD spectrum of the C215A mutant PAS-A-mPer2 protein was markedly different from that of the wild-type protein. On the basis of the data, we propose that PAS-A-mPer2 is a heme-sensor protein in which Cys215 is the heme axial ligand.
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Affiliation(s)
- Kenichi Kitanishi
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku UniVersity, Katahira, Sendai 980-8577, Japan
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