1
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Thesbjerg MN, Sundekilde UK, Poulsen NA, Larsen LB, Nielsen SDH. A novel proteomic approach for the identification and relative quantification of disulfide-bridges in the human milk proteome. J Proteomics 2024; 301:105194. [PMID: 38723850 DOI: 10.1016/j.jprot.2024.105194] [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: 11/29/2023] [Revised: 04/26/2024] [Accepted: 05/05/2024] [Indexed: 05/13/2024]
Abstract
This study explores the disulfide bridges present in the human milk proteome by a novel approach permitting both positional identification and relative quantification of the disulfide bridges. Human milk from six donors was subjected to trypsin digestion without reduction. The digested human milk proteins were analyzed by nanoLC-timsTOF Pro combined with data analysis using xiSEARCH. A total of 85 unique disulfide bridges were identified in 25 different human milk proteins. The total relative abundance of disulfide bridge-containing peptides constituted approximately 5% of the total amount of tryptic-peptides. Seven inter-molecular disulfide bridges were identified between either α-lactalbumin and lactotransferrin (5) or αS1-casein and κ-casein (2). All cysteines involved in the observed disulfide bridges of α-lactalbumin and lactotransferrin were mapped onto protein models using AlphaFold2 Multimer to estimate the length of the observed disulfide bridges. The lengths of the disulfide bridges of lactotransferrin indicate a potential for multi- or poly-merization of lactotransferrin. The high number of intramolecular lactotransferrin disulfide bridges identified, suggests that these are more heterogeneous than previously presumed. SIGNIFICANCE: Disulfide-bridges in the human milk proteome are an often overseen post-transaltional modification. Thus, mapping the disulfide-bridges, their positions and relative abundance, are valuable new knowledge needed for an improved understanding of human milk protein behaviour. Although glycosylation and phosphorylation have been described, even less information is available on the disulfide bridges and the disulfide-bridge derived protein complexes. This is important for future work in precision fermentation for recombinant production of human milk proteins, as this will highlight which disulfide-bridges are naturally occouring in human milk proteins. Further, this knowledge would be of value for the infant formula industry as it provides more information on how to humanize bovine-milk based infant formula. The novel method developed here can be broadly applied in other biological systems as the disulfid-brigdes are important for the structure and functionality of proteins.
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Affiliation(s)
- Martin Nørmark Thesbjerg
- Department of Food Science, Aarhus University, Agro Food Park 48, DK-8200 Aarhus N, Denmark; Sino-Danish College (SDC), University of Chinese Academy of Science, Huairou District, Beijing 101408, China.
| | | | - Nina Aagaard Poulsen
- Department of Food Science, Aarhus University, Agro Food Park 48, DK-8200 Aarhus N, Denmark
| | - Lotte Bach Larsen
- Department of Food Science, Aarhus University, Agro Food Park 48, DK-8200 Aarhus N, Denmark
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2
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Benjamín-Rivera J, Otero MP, Tinoco AD. Reinforcing Protein Biochemistry: A Two-Week Experiment Studying Iron(III) Binding by the Transferrin Protein through Stoichiometric Determination, Stability Analysis, and Visualization of the Binding Site. JOURNAL OF CHEMICAL EDUCATION 2024; 101:1656-1664. [PMID: 38654892 PMCID: PMC11033862 DOI: 10.1021/acs.jchemed.3c01016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Revised: 02/29/2024] [Accepted: 03/01/2024] [Indexed: 04/26/2024]
Abstract
The two-week protein biochemistry experience described herein focuses on reinforcing key biochemical concepts and achieving significant learning domain accomplishments for students (Content Knowledge, Logical Mathematical Reasoning, Visualization, Information Literacy, and Knowledge Integration) and valuable teaching opportunities for instructors. The experience encompasses an exploration of the transport protein serum transferrin as an important regulator of Fe(III) biochemistry and incorporates techniques to assess protein-metal stoichiometry and protein stability and to perform molecular visualization. Students gain practical experience in utilizing spectrophotometric analysis for constructing stoichiometric curves, in performing urea-PAGE, and in applying the PyMOL program to evaluate metal coordination at a protein binding site and the associated protein structural change. The learning and teaching accomplishments provide valuable skills that can be extended into research and translated to other teaching formats.
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Affiliation(s)
- Josué
A. Benjamín-Rivera
- Department
of Chemistry, University of Puerto Rico, Río Piedras Campus, Río Piedras, Puerto Rico 00931, United States
| | - Mariela Pérez Otero
- Department
of Biology, University of Puerto Rico, Río Piedras Campus, Río Piedras, Puerto Rico 00931, United States
| | - Arthur D. Tinoco
- Department
of Chemistry, University of Puerto Rico, Río Piedras Campus, Río Piedras, Puerto Rico 00931, United States
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3
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Kumar R, Sharma D, Kumar N, Kumari B, Kumar S, Kumar R. Substitution of carbonate by non-physiological synergistic anion modulates the stability and iron release kinetics of serum transferrin. BIOCHIMICA ET BIOPHYSICA ACTA. PROTEINS AND PROTEOMICS 2023; 1871:140856. [PMID: 36252939 DOI: 10.1016/j.bbapap.2022.140856] [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: 07/14/2022] [Revised: 09/26/2022] [Accepted: 10/04/2022] [Indexed: 11/06/2022]
Abstract
Serum transferrin (sTf) is a bi-lobal protein. Each lobe of sTf binds one Fe3+ ion in the presence of a synergistic anion. Physiologically, carbonate is the main synergistic anion but other anions such as oxalate, malonate, glycolate, maleate, glycine, etc. can substitute for carbonate in vitro. The present work provides the possible pathways by which the substitution of carbonate with oxalate affects the structural, kinetic, thermodynamic, and functional properties of blood plasma sTf. Analysis of equilibrium experiments measuring iron release and structural unfolding of carbonate and oxalate bound diferric-sTf (Fe2sTf) as a function of pH, urea concentration, and temperature reveal that the structural and iron-centers stability of Fe2sTf increase by substitution of carbonate with oxalate. Analysis of isothermal titration calorimetry (ITC) scans showed that the affinity of Fe3+ with apo-sTf is enhanced by substituting carbonate with oxalate. Analysis of kinetic and thermodynamic parameters measured for the iron release from the carbonate and oxalate bound monoferric-N-lobe of sTf (FeNsTf) and Fe2sTf at pH 7.4 and pH 5.6 reveals that the substitution of carbonate with oxalate inhibits/retards the iron release via increasing the enthalpic barriers.
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Affiliation(s)
- Rajesh Kumar
- School of Chemistry and Biochemistry, Thapar University, Patiala 147004, India
| | - Deepak Sharma
- Council of Scientific and Industrial Research-Institute of Microbial Technology, Sector 39A, Chandigarh, India
| | - Navinder Kumar
- Council of Scientific and Industrial Research-Institute of Microbial Technology, Sector 39A, Chandigarh, India
| | - Beeta Kumari
- Deparment of Chemistry, School of Basic Sciences, Central University of Punjab, Ghudda, Bathinda 151401, India
| | - Sanjeev Kumar
- Deparment of Chemistry, School of Basic Sciences, Central University of Punjab, Ghudda, Bathinda 151401, India
| | - Rajesh Kumar
- Deparment of Chemistry, School of Basic Sciences, Central University of Punjab, Ghudda, Bathinda 151401, India; School of Chemistry and Biochemistry, Thapar University, Patiala 147004, India.
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4
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Azarkh M, Gast P, Mason AB, Groenen EJJ, Mathies G. Analysis of the EPR spectra of transferrin: the importance of a zero-field-splitting distribution and 4 th-order terms. Phys Chem Chem Phys 2019; 21:16937-16948. [PMID: 31339131 DOI: 10.1039/c9cp02626f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Multi-frequency EPR spectroscopy can provide high-level structural information on high-spin Fe3+ sites in proteins and enzymes. Unfortunately, analysis of the EPR spectra of these spin systems is hindered by the presence of broad distributions in the zero-field-splitting (ZFS) parameters, which reflect conformational heterogeneity of the iron sites. We present the analysis of EPR spectra of high-spin Fe3+ bound to human serum transferrin. We apply a method termed the grid-of-errors to extract the distributions of the individual ZFS parameters from EPR spectra recorded in the high-field limit at a microwave frequency of 275 GHz. Study of a series of transferrin variants shows that the ZFS distributions are as characteristic of the structure of a high-spin Fe3+ site as the ZFS parameters themselves. Simulations based on the extracted ZFS distributions reproduce spectra recorded at 34 GHz (Q band) and 9.7 GHz (X band), including subtle variations that were previously difficult to quantify. The X-band spectrum of transferrin shows a characteristic double peak, which has puzzled researchers for decades. We show that the double peak is uniquely related to the term B4-3O4-3(S) in the spin Hamiltonian. Our method is generally applicable in the analysis of spectra that arise from a broad distribution of parameters.
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Affiliation(s)
- Mykhailo Azarkh
- Department of Chemistry, University of Konstanz, 78464 Konstanz, Germany.
| | - Peter Gast
- Department of Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, PO Box 9504, 2300 RA Leiden, The Netherlands
| | - Anne B Mason
- Department of Biochemistry, University of Vermont College of Medicine, Burlington, VT 05405, USA
| | - Edgar J J Groenen
- Department of Physics, Huygens-Kamerlingh Onnes Laboratory, Leiden University, PO Box 9504, 2300 RA Leiden, The Netherlands
| | - Guinevere Mathies
- Department of Chemistry, University of Konstanz, 78464 Konstanz, Germany.
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5
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The effect of glycosylation on the transferrin structure: A molecular dynamic simulation analysis. J Theor Biol 2016; 404:73-81. [PMID: 27235585 DOI: 10.1016/j.jtbi.2016.05.024] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Revised: 05/10/2016] [Accepted: 05/18/2016] [Indexed: 11/20/2022]
Abstract
Transferrins have been defined by the highly cooperative binding of iron and a carbonate anion to form a Fe-CO3-Tf ternary complex. As such, the layout of the binding site residues affects transferrin function significantly; In contrast to N-lobe, C-lobe binding site of the transferrin structure has been less characterized and little research which surveyed the interaction of carbonate with transferrin in the C-lobe binding site has been found. In the present work, molecular dynamic simulation was employed to gain access into the molecular level understanding of carbonate binding site and their interactions in each lobe. Residues responsible for carbonate binding of transferrin structure were pointed out. In addition, native human transferrin is a glycoprotein that two N-linked complex glycan chains located in the C-lobe. Usually, in the molecular dynamic simulation for simplifying, glycan is removed from the protein structure. Here, we explore the effect of glycosylation on the transferrin structure. Glycosylation appears to have an effect on the layout of the binding site residue and transferrin structure. On the other hand, sometimes the entire transferrin formed by separated lobes that it allows the results to be interpreted in a straightforward manner rather than more parameters required for full length protein. But, it should be noted that there are differences between the separated lobe and full length transferrin, hence, a comparative analysis by the molecular dynamic simulation was performed to investigate such structural variations. Results revealed that separation in C-lobe caused a significant structural variation in comparison to N-lobe. Consequently, the separated lobes and the full length one are different, showing the importance of the interlobe communication and the impact of the lobes on each other in the transferrin structure.
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6
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Mayeur S, Spahis S, Pouliot Y, Levy E. Lactoferrin, a Pleiotropic Protein in Health and Disease. Antioxid Redox Signal 2016; 24:813-36. [PMID: 26981846 DOI: 10.1089/ars.2015.6458] [Citation(s) in RCA: 105] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
SIGNIFICANCE Lactoferrin (Lf) is a nonheme iron-binding glycoprotein strongly expressed in human and bovine milk and it plays many functions during infancy such as iron homeostasis and defense against microorganisms. In humans, Lf is mainly expressed in mucosal epithelial and immune cells. Growing evidence suggests multiple physiological roles for Lf after weaning. RECENT ADVANCES The aim of this review is to highlight the recent advances concerning multifunctional Lf activities. CRITICAL ISSUES First, we will provide an overview of the mechanisms related to Lf intrinsic synthesis or intestinal absorption as well as its interaction with a wide spectrum of mammalian receptors and distribution in organs and cell types. Second, we will discuss the large variety of its physiological functions such as iron homeostasis, transportation, immune regulation, oxidative stress, inflammation, and apoptosis while specifying the mechanisms of action. Third, we will focus on its recent physiopathology implication in metabolic disorders, including obesity, type 2 diabetes, and cardiovascular diseases. Additional efforts are necessary before suggesting the potential use of Lf as a diagnostic marker or as a therapeutic tool. FUTURE DIRECTIONS The main sources of Lf in human cardiometabolic disorders should be clarified to identify new perspectives for future research and develop new strategies using Lf in therapeutics. Antioxid. Redox Signal. 24, 813-836.
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Affiliation(s)
- Sylvain Mayeur
- 1 Research Centre, CHU Ste-Justine, Université de Montréal , Montreal, Canada .,2 Institute of Nutraceuticals and Functional Foods (INAF) , Université Laval, Quebec, Canada
| | - Schohraya Spahis
- 1 Research Centre, CHU Ste-Justine, Université de Montréal , Montreal, Canada .,2 Institute of Nutraceuticals and Functional Foods (INAF) , Université Laval, Quebec, Canada .,3 Department of Nutrition, Université de Montréal , Montreal, Canada
| | - Yves Pouliot
- 3 Department of Nutrition, Université de Montréal , Montreal, Canada
| | - Emile Levy
- 1 Research Centre, CHU Ste-Justine, Université de Montréal , Montreal, Canada .,2 Institute of Nutraceuticals and Functional Foods (INAF) , Université Laval, Quebec, Canada .,3 Department of Nutrition, Université de Montréal , Montreal, Canada
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7
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Wang M, Lai TP, Wang L, Zhang H, Yang N, Sadler PJ, Sun H. “Anion clamp” allows flexible protein to impose coordination geometry on metal ions. Chem Commun (Camb) 2015; 51:7867-70. [DOI: 10.1039/c4cc09642h] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
X-ray crystal structures of human serum transferrin (77 kDa) with YbIII or FeIII bound to the C-lobe and malonate as the synergistic anion show that the large YbIII ion causes the expansion of the metal binding pocket while octahedral metal coordination geometry is preserved, an unusual geometry for a lanthanide ion.
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Affiliation(s)
- Minji Wang
- Department of Chemistry
- The University of Hong Kong
- Hong Kong SAR
- P. R. China
| | - Tsz Pui Lai
- Department of Chemistry
- The University of Hong Kong
- Hong Kong SAR
- P. R. China
| | - Li Wang
- Department of Chemistry
- The University of Hong Kong
- Hong Kong SAR
- P. R. China
- Department of Chemistry
| | - Hongmin Zhang
- Department of Biology and Shenzhen Key Laboratory of Cell Microenvironment
- South University of Science and Technology of China
- Shenzhen 518055
- P. R. China
- Department of Chemistry
| | - Nan Yang
- Department of Chemistry
- The University of Hong Kong
- Hong Kong SAR
- P. R. China
- Department of Physiology
| | - Peter J. Sadler
- Department of Chemistry
- The University of Hong Kong
- Hong Kong SAR
- P. R. China
- Department of Chemistry
| | - Hongzhe Sun
- Department of Chemistry
- The University of Hong Kong
- Hong Kong SAR
- P. R. China
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8
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Majka G, Śpiewak K, Kurpiewska K, Heczko P, Stochel G, Strus M, Brindell M. A high-throughput method for the quantification of iron saturation in lactoferrin preparations. Anal Bioanal Chem 2013; 405:5191-200. [PMID: 23604471 PMCID: PMC3656221 DOI: 10.1007/s00216-013-6943-9] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Revised: 03/14/2013] [Accepted: 03/25/2013] [Indexed: 11/29/2022]
Abstract
Lactoferrin is considered as a part of the innate immune system that plays a crucial role in preventing bacterial growth, mostly via an iron sequestration mechanism. Recent data show that bovine lactoferrin prevents late-onset sepsis in preterm very low birth weight neonates by serving as an iron chelator for some bacterial strains; thus, it is very important to control the iron saturation level during diet supplementation. An accurate estimation of lactoferrin iron saturation is essential not only because of its clinical applications but also for a wide range of biochemical experiments. A comprehensive method for the quantification of iron saturation in lactoferrin preparations was developed to obtain a calibration curve enabling the determination of iron saturation levels relying exclusively on the defined ratio of absorbances at 280 and 466 nm (A280/466). To achieve this goal, selected techniques such as spectrophotometry, ELISA, and ICP-MS were combined. The ability to obtain samples of lactoferrin with determination of its iron content in a simple and fast way has been proven to be very useful. Furthermore, a similar approach could easily be implemented to facilitate the determination of iron saturation level for other metalloproteins in which metal binding results in the appearance of a distinct band in the visible part of the spectrum.
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Affiliation(s)
- Grzegorz Majka
- Department of Inorganic Chemistry, Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow, Poland
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9
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Iron and bismuth bound human serum transferrin reveals a partially-opened conformation in the N-lobe. Sci Rep 2012; 2:999. [PMID: 23256035 PMCID: PMC3525939 DOI: 10.1038/srep00999] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2012] [Accepted: 11/26/2012] [Indexed: 11/17/2022] Open
Abstract
Human serum transferrin (hTF) binds Fe(III) tightly but reversibly, and delivers it to cells via a receptor-mediated endocytosis process. The metal-binding and release result in significant conformational changes of the protein. Here, we report the crystal structures of diferric-hTF (FeNFeC-hTF) and bismuth-bound hTF (BiNFeC-hTF) at 2.8 and 2.4 Å resolutions respectively. Notably, the N-lobes of both structures exhibit unique “partially-opened” conformations between those of the apo-hTF and holo-hTF. Fe(III) and Bi(III) in the N-lobe coordinate to, besides anions, only two (Tyr95 and Tyr188) and one (Tyr188) tyrosine residues, respectively, in contrast to four residues in the holo-hTF. The C-lobe of both structures are fully closed with iron coordinating to four residues and a carbonate. The structures of hTF observed here represent key conformers captured in the dynamic nature of the transferrin family proteins and provide a structural basis for understanding the mechanism of metal uptake and release in transferrin families.
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10
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Kumar R, Mauk AG. Protonation and Anion Binding Control the Kinetics of Iron Release from Human Transferrin. J Phys Chem B 2012; 116:3795-807. [DOI: 10.1021/jp205879h] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Rajesh Kumar
- Department of Biochemistry
and Molecular Biology and the Centre for
Blood Research, Life Sciences Centre, 2350 Health Sciences
Mall, University of British Columbia, Vancouver,
BC V6T 1Z3 Canada
- School of Chemistry
and Biochemistry, Thapar University, Patiala 147004, India
| | - A. Grant Mauk
- Department of Biochemistry
and Molecular Biology and the Centre for
Blood Research, Life Sciences Centre, 2350 Health Sciences
Mall, University of British Columbia, Vancouver,
BC V6T 1Z3 Canada
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11
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Mizutani K, Toyoda M, Mikami B. X-ray structures of transferrins and related proteins. Biochim Biophys Acta Gen Subj 2011; 1820:203-11. [PMID: 21855609 DOI: 10.1016/j.bbagen.2011.08.003] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 07/21/2011] [Accepted: 08/03/2011] [Indexed: 11/25/2022]
Abstract
BACKGROUND Transferrins are a group of iron-binding proteins including serum transferrin, lactoferrin and ovotransferrin. SCOPE OF REVIEW The structures of transferrins are discussed. GENERAL SIGNIFICANCE The typical transferrin molecules are folded into two homologous lobes. X-ray crystallography revealed that each lobe is further divided into two similarly sized domains, and that an iron-binding site is contained within the inter-domain cleft. The six iron coordination sites are occupied by four residues and a bidentate carbonate anion. MAJOR CONCLUSIONS The structures of the apo- and holo-forms revealed that the transferrins undergo a large-scale conformational change upon the uptake and release of irons: domains rotate as rigid bodies around a screw axis passing through inter-domain contacts. The iron-release mechanism of transferrin N-lobe is also revealed by X-ray crystallography; two basic residues in two domains form an unusual hydrogen bond in neutral pH, and the bond should be broken and facilitate iron release at a low pH of the endosome. For ovotransferrin, the iron release kinetics of two lobes correspond well with the numbers of anion binding sites found in crystal structures. The structures of transferrins bound to other metals revealed that the flexibility of the transferrin structure allows the ability to bind to other metals. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.
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Affiliation(s)
- Kimihiko Mizutani
- Laboratory of Applied Structural Biology, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Uji, Kyoto 611-0011, Japan.
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12
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Harris WR. Anion binding properties of the transferrins. Implications for function. Biochim Biophys Acta Gen Subj 2011; 1820:348-61. [PMID: 21846492 DOI: 10.1016/j.bbagen.2011.07.017] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Revised: 07/25/2011] [Accepted: 07/28/2011] [Indexed: 10/17/2022]
Abstract
BACKGROUND Since the transferrins have been defined by the highly cooperative binding of Fe(3+) and a carbonate anion to form an Fe-CO(3)-Tf ternary complex, the focus has been on synergistic anion binding. However, there are other types of anion binding with both apotransferrin and diferric transferrin that affect metal binding and release. SCOPE OF REVIEW This review covers the binding of anions to the apoprotein, as well as the formation and structure of Fe-anion-transferrin ternary complexes. It also covers interactions between ferric transferrin and non-synergistic anions that appear to be important in vivo. GENERAL SIGNIFICANCE The interaction of anions with apotransferrin can alter the effective metal binding constants, which can affect the transport of metal ions in serum. These interactions also play a role in iron release under physiological conditions. MAJOR CONCLUSIONS Apotransferrin binds a variety of anions with no special selectivity for carbonate. The selectivity for carbonate as a synergistic anion is associated with the iron binding reaction. Conformational changes in the binding of the synergistic carbonate and competition from non-synergistic anions both play a role in intracellular iron release. Anion competition also occurs in serum and reduces the effective metal binding affinity of Tf. Lastly, anions bind to allosteric sites (KISAB sites) on diferric transferrin and alter the rates of iron release. The KISAB sites have not been well-characterized, but kinetic studies on iron release from mutant transferrins indicate that there are likely to be multiple KISAB sites for each lobe of transferrin. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.
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Affiliation(s)
- Wesley R Harris
- Department of Chemistry & Biochemistry, University of Missouri-St. Louis, St. Louis, MO 63121, USA.
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13
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Eckenroth BE, Mason AB, McDevitt ME, Lambert LA, Everse SJ. The structure and evolution of the murine inhibitor of carbonic anhydrase: a member of the transferrin superfamily. Protein Sci 2010; 19:1616-26. [PMID: 20572014 PMCID: PMC2975126 DOI: 10.1002/pro.439] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The original signature of the transferrin (TF) family of proteins was the ability to bind ferric iron with high affinity in the cleft of each of two homologous lobes. However, in recent years, new family members that do not bind iron have been discovered. One new member is the inhibitor of carbonic anhydrase (ICA), which as its name indicates, binds to and strongly inhibits certain isoforms of carbonic anhydrase. Recently, mouse ICA has been expressed as a recombinant protein in a mammalian cell system. Here, we describe the 2.4 Å structure of mouse ICA from a pseudomerohedral twinned crystal. As predicted, the structure is bilobal, comprised of two α-β domains per lobe typical of the other family members. As with all but insect TFs, the structure includes the unusual reverse γ-turn in each lobe. The structure is consistent with the fact that introduction of two mutations in the N-lobe of murine ICA (mICA) (W124R and S188Y) allowed it to bind iron with high affinity. Unexpectedly, both lobes of the mICA were found in the closed conformation usually associated with presence of iron in the cleft, and making the structure most similar to diferric pig TF. Two new ICA family members (guinea pig and horse) were identified from genomic sequences and used in evolutionary comparisons. Additionally, a comparison of selection pressure (dN/dS) on functional residues reveals some interesting insights into the evolution of the TF family including that the N-lobe of lactoferrin may be in the process of eliminating its iron binding function.
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Affiliation(s)
- Brian E Eckenroth
- Department of Biochemistry, University of VermontBurlington, Vermont 05405
| | - Anne B Mason
- Department of Biochemistry, University of VermontBurlington, Vermont 05405
| | - Meghan E McDevitt
- Department of Biology, Chatham UniversityPittsburgh, Pennsylvania 15232
| | - Lisa A Lambert
- Department of Biology, Chatham UniversityPittsburgh, Pennsylvania 15232
| | - Stephen J Everse
- Department of Biochemistry, University of VermontBurlington, Vermont 05405,*Correspondence to: Stephen J. Everse, Department of Biochemistry, University of Vermont, College of Medicine, 89 Beaumont Ave, Burlington, VT 05405. E-mail:
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14
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Byrne SL, Chasteen ND, Steere AN, Mason AB. The unique kinetics of iron release from transferrin: the role of receptor, lobe-lobe interactions, and salt at endosomal pH. J Mol Biol 2009; 396:130-40. [PMID: 19917294 DOI: 10.1016/j.jmb.2009.11.023] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Revised: 11/04/2009] [Accepted: 11/10/2009] [Indexed: 10/20/2022]
Abstract
Transferrins are a family of bilobal iron-binding proteins that play the crucial role of binding ferric iron and keeping it in solution, thereby controlling the levels of this important metal. Human serum transferrin (hTF) carries one iron in each of two similar lobes. Understanding the detailed mechanism of iron release from each lobe of hTF during receptor-mediated endocytosis has been extremely challenging because of the active participation of the transferrin receptor (TFR), salt, a chelator, lobe-lobe interactions, and the low pH within the endosome. Our use of authentic monoferric hTF (unable to bind iron in one lobe) or diferric hTF (with iron locked in one lobe) provided distinct kinetic end points, allowing us to bypass many of the previous difficulties. The capture and unambiguous assignment of all kinetic events associated with iron release by stopped-flow spectrofluorimetry, in the presence and in the absence of the TFR, unequivocally establish the decisive role of the TFR in promoting efficient and balanced iron release from both lobes of hTF during one endocytic cycle. For the first time, the four microscopic rate constants required to accurately describe the kinetics of iron removal are reported for hTF with and without the TFR. Specifically, at pH 5.6, the TFR enhances the rate of iron release from the C-lobe (7-fold to 11-fold) and slows the rate of iron release from the N-lobe (6-fold to 15-fold), making them more equivalent and producing an increase in the net rate of iron removal from Fe(2)hTF. Calculated cooperativity factors, in addition to plots of time-dependent species distributions in the absence and in the presence of the TFR, clearly illustrate the differences. Accurate rate constants for the pH and salt-induced conformational changes in each lobe precisely delineate how delivery of iron within the physiologically relevant time frame of 2 min might be accomplished.
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Affiliation(s)
- Shaina L Byrne
- Department of Biochemistry, College of Medicine, University of Vermont, 89 Beaumont Avenue, Burlington, VT 05405, USA
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15
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Kinetics and mechanism of exogenous anion exchange in FeFbpA-NTA: significance of periplasmic anion lability and anion binding activity of ferric binding protein A. J Biol Inorg Chem 2009; 15:237-48. [PMID: 19813031 DOI: 10.1007/s00775-009-0589-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2009] [Accepted: 09/01/2009] [Indexed: 10/20/2022]
Abstract
The bacterial transferrin ferric binding protein A (FbpA) requires an exogenous anion to facilitate iron sequestration, and subsequently to shuttle the metal across the periplasm to the cytoplasmic membrane. In the diverse conditions of the periplasm, numerous anions are known to be present. Prior in vitro experiments have demonstrated the ability of multiple anions to fulfill the synergistic iron-binding requirement, and the identity of the bound anion has been shown to modulate important physicochemical properties of iron-bound FbpA (FeFbpA). Here we address the kinetics and mechanism of anion exchange for the FeFbpA-nitrilotriacetate (NTA) assembly with several biologically relevant anions (citrate, oxalate, phosphate, and pyrophosphate), with nonphysiologic NTA serving as a representative synergistic anion/chelator. The kinetic data are consistent with an anion-exchange process that occurs in multiple steps, dependent on the identity of both the entering anion and the leaving anion. The exchange mechanism may proceed either as a direct substitution or through an intermediate FeFbpA-X* assembly based on anion (X) identity. Our kinetic results further develop an understanding of exogenous anion lability in the periplasm, as well as address the final step of the iron-free FbpA (apo-FbpA)/Fe(3+) sequestration mechanism. Our results highlight the kinetic significance of the FbpA anion binding site, demonstrating a correlation between apo-FbpA/anion affinity and the FeFbpA rate of anion exchange, further supporting the requirement of an exogenous anion to complete tight sequestration of iron by FbpA, and developing a mechanism for anion exchange within FeFbpA that is dependent on the identity of both the entering anion and the leaving anion.
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16
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17
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Mason AB, Judson GL, Bravo MC, Edelstein A, Byrne SL, James NG, Roush ED, Fierke CA, Bobst CE, Kaltashov IA, Daughtery MA. Evolution reversed: the ability to bind iron restored to the N-lobe of the murine inhibitor of carbonic anhydrase by strategic mutagenesis. Biochemistry 2008; 47:9847-55. [PMID: 18712936 DOI: 10.1021/bi801133d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The murine inhibitor of carbonic anhydrase (mICA) is a member of the superfamily related to the bilobal iron transport protein transferrin (TF), which binds a ferric ion within a cleft in each lobe. Although the gene encoding ICA in humans is classified as a pseudogene, an apparently functional ICA gene has been annotated in mice, rats, cows, pigs, and dogs. All ICAs lack one (or more) of the amino acid ligands in each lobe essential for high-affinity coordination of iron and the requisite synergistic anion, carbonate. The reason why ICA family members have lost the ability to bind iron is potentially related to acquiring a new function(s), one of which is inhibition of certain carbonic anhydrase (CA) isoforms. A recombinant mutant of the mICA (W124R/S188Y) was created with the goal of restoring the ligands required for both anion (Arg124) and iron (Tyr188) binding in the N-lobe. Absorption and fluorescence spectra definitively show that the mutant binds ferric iron in the N-lobe. Electrospray ionization mass spectrometry confirms the presence of both ferric iron and carbonate. At the putative endosomal pH of 5.6, iron is released by two slow processes indicative of high-affinity coordination. Induction of specific iron binding implies that (1) the structure of mICA resembles those of other TF family members and (2) the N-lobe can adopt a conformation in which the cleft closes when iron binds. Because the conformational change in the N-lobe indicated by metal binding does not impact the inhibitory activity of mICA, inhibition of CA was tentatively assigned to the C-lobe. Proof of this assignment is provided by limited trypsin proteolysis of porcine ICA.
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Affiliation(s)
- Anne B Mason
- Department of Biochemistry, College of Medicine, University of Vermont, Burlington, Vermont 05405, USA.
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18
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Heymann JJ, Weaver KD, Mietzner TA, Crumbliss AL. Sulfate as a synergistic anion facilitating iron binding by the bacterial transferrin FbpA: the origins and effects of anion promiscuity. J Am Chem Soc 2007; 129:9704-12. [PMID: 17630737 PMCID: PMC3674819 DOI: 10.1021/ja0709268] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The ferric binding protein, FbpA, has been demonstrated to facilitate the transport of naked Fe3+ across the periplasmic space of several Gram-negative bacteria. The sequestration of iron by FbpA is facilitated by the presence of a synergistic anion, such as phosphate or sulfate. Here we report the sequestration of Fe3+ by FbpA in the presence of sulfate, at an assumed periplasmic pH of 6.5 to form FeFbpA-SO4 with K'(eff) = 1.7 x 10(16) M(-1) (at 20 degrees C, 50 mM MES, 200 mM KCl). The iron affinity of the FeFbpA-SO4 protein assembly is 2 orders of magnitude lower than when bound with phosphate and is the lowest of any of the FeFbpA-X assemblies yet reported. Iron reduction at the cytosolic membrane receptor may be an essential aspect of the periplasmic iron-transport process, and with an E(1/2) of -158 mV (NHE), FeFbpA-SO4 is the most easily reduced of all FeFbpA-X assemblies yet studied. The variation of FeFbpA-X assembly stability (K'(eff)) and ease of reduction (E(1/2)) with differing synergistic anions X(n-) are correlated over a range of 14 kJ, suggesting that the variations in redox potentials are due to stabilization of Fe3+ in FeFbpA-X by X(n-). Anion promiscuity of FbpA in the diverse composition of the periplasmic space is illustrated by the ex vivo exchange kinetics of FeFbpA-SO4 with phosphate and arsenate, where first-order kinetics with respect to FeFbpA-SO4 (k = 30 s(-1)) are observed at pH 6.5, independent of entering anion concentration and identity. Anion lability and influence on the iron affinity and reduction potential for FeFbpA-X support the hypothesis that synergistic anion exchange may be an important regulator in iron delivery to the cytosol. This structural and thermodynamic analysis of anion binding in FeFbpA-X provides additional insight into anion promiscuity and importance.
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Affiliation(s)
- J. J. Heymann
- Department of Chemistry, Duke University, Durham, NC 27708−0346
| | - K. D. Weaver
- Department of Chemistry, Duke University, Durham, NC 27708−0346
| | - T. A. Mietzner
- Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - A. L. Crumbliss
- Department of Chemistry, Duke University, Durham, NC 27708−0346
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19
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Brook CE, Harris WR, Spilling CD, Peng W, Harburn JJ, Srisung S. Effect of Ligand Structure on the Pathways for Iron Release from Human Serum Transferrin. Inorg Chem 2005; 44:5183-91. [PMID: 15998048 DOI: 10.1021/ic050411m] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Rate constants for the removal of iron from N-terminal monoferric transferrin have been measured for a series of phosphate and phosphonocarboxylic acids in pH 7.4 0.1 M hepes buffer at 25 degrees C. The bidentate ligands pyrophosphate and phosphonoacetic acid (PAA) show a combination of saturation and first-order kinetics with respect to the ligand concentration. Similar results are observed following a single substitution at the 2-position of PAA to give 2-benzyl-PAA and phosphonosuccinic acid. In contrast, disubstitution at the 2-position to form 2,2-dibenzyl-PAA leads to a marked reduction in iron removal via the first-order pathway. Rate constants were also measured for tripolyphosphate and phosphonodiacetic acid, which are elongated versions of PP(i) and PAA. In both cases, this elongation completely eliminates the first-order component for iron release while having relatively little impact on the saturation pathway. The sensitivity of the first-order component to the structure of the ligand strongly indicates that this pathway involves the binding of the ligand to a specific site on the protein and cannot be attributed to changes in the overall ionic strength of the solution as the ligand concentration increases. It is proposed that this structural sensitivity reflects steric restrictions on the ability of the incoming ligand to substitute for the synergistic carbonate anion to form a relatively unstable Fe-ligand-Tf ternary intermediate, which then dissociates to FeL and apoTf.
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Affiliation(s)
- Claire E Brook
- Department of Chemistry & Biochemistry, University of Missouri-St. Louis, St. Louis, Missouri 63121-4499, USA
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20
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Halbrooks PJ, Mason AB, Adams TE, Briggs SK, Everse SJ. The Oxalate Effect on Release of Iron from Human Serum Transferrin Explained. J Mol Biol 2004; 339:217-26. [PMID: 15123433 DOI: 10.1016/j.jmb.2004.03.049] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2003] [Revised: 03/16/2004] [Accepted: 03/16/2004] [Indexed: 11/26/2022]
Abstract
A unique feature of the mechanism of iron binding to the transferrin (TF) family is the synergistic relationship between metal binding and anion binding. Little or no iron will bind to the protein without concomitant binding of an anion, physiologically identified as carbonate. Substitution of oxalate for carbonate produces no significant changes in polypeptide folding or domain orientation in the N-lobe of human serum TF (hTF) as revealed by our 1.2A structure. The oxalate is able to bind to the iron in a symmetric bidentate fashion, which, combined with the low pK(a) of the oxalate anion, makes iron displacement more difficult as documented by both iron release kinetic and equilibrium data. Characterization of an N-lobe in which the arginine at position 124 is mutated to alanine reveals that the stabilizing effect of oxalate is even greater in this mutant and nearly cancels the destabilizing effect of the mutation. Importantly, incorporation of oxalate as the synergistic anion appears to completely inhibit removal of iron from recombinant full-length hTF by HeLa S(3) cells, strongly indicating that oxalate also replaces carbonate in the C-lobe to form a stable complex. Kinetic studies confirm this claim. The combination of structural and functional data provides a coherent delineation of the effect of oxalate binding on hTF and rationalizes the results of many previous studies. In the context of iron uptake by cells, substitution of carbonate by oxalate effectively locks the iron into each lobe of hTF, thereby interfering with normal iron metabolism.
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Affiliation(s)
- Peter J Halbrooks
- Department of Biochemistry, College of Medicine, University of Vermont, 89 Beaumont Avenue, Burlington, VT 05405, USA
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21
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Ohashi A, Murata E, Yamamoto K, Majima E, Sano E, Le QT, Katunuma N. New functions of lactoferrin and beta-casein in mammalian milk as cysteine protease inhibitors. Biochem Biophys Res Commun 2003; 306:98-103. [PMID: 12788072 DOI: 10.1016/s0006-291x(03)00917-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We found new inhibitory function of lactoferrin and beta-casein in milk against cysteine proteases using reverse zymography. The inhibition of cathepsin L by lactoferrin was strongest and the inhibition kinetics were of a non-competitive type. Heat denatured lactoferrin lost the inhibitory activity completely, therefore the tertiary structure is essential to show the inhibition. Native lactoferrin was not degraded by papain during the assay condition. The intramolecular peptide, Y(679)-K(695), of lactoferrin is an active domain and the synthesized peptide inhibited cysteine proteases. The Y(679)-K(695) peptide showed 90% homology with the sequences of a common active site of cystatin family. beta-Casein and the active domain, synthesized L(133)-Q(151), peptide inhibited cysteine proteases. Lactoferrin and beta-casein in milk might play a role in antiseptic and antiinfectious functions due to cysteine protease inhibition of bacteria and viruses.
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Affiliation(s)
- A Ohashi
- Institute for Health Sciences, Tokushima Bunri University, Yamashiro-cho, 770-8514, Tokushima-City, Japan
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22
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Shongwe MS, Al-Hatmi SKM, Marques HM, Smith R, Nukada R, Mikuriya M. Complexes of cobalt(iii) with phenolate-containing polydentate ligands and bovine serum apo-transferrin: towards creating spectroscopic models for cobalt(iii)–tyrosinate interactions. ACTA ACUST UNITED AC 2002. [DOI: 10.1039/b202161g] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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23
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Breuer W, Cabantchik ZI. A fluorescence-based one-step assay for serum non-transferrin-bound iron. Anal Biochem 2001; 299:194-202. [PMID: 11730343 DOI: 10.1006/abio.2001.5378] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We introduce a method for monitoring non-transferrin-bound iron (NTBI), a labile and potentially toxic form of serum iron associated with imbalanced iron metabolism. The assay employs fluorescein-labeled apotransferrin (Fl-aTf), which undergoes fluorescence quenching upon binding iron. It has the advantages of simplicity, high sensitivity, and detection of those forms of NTBI that persist in sera with low transferrin saturations. Since NTBI is not readily available for detection, it is mobilized by 10 mM oxalate. Endogenous serum apotransferrin, capable of binding oxalate-mobilized NTBI, is blocked by 0.1 mM gallium(III). This metal, like iron, binds to Fl-aTf, but it neither quenches its fluorescence nor interferes with quenching by iron. Serum and reagent containing oxalate, Ga(Cl)(3), and Fl-aTf are mixed in multiwell plates and fluorescence is determined after 1 h in a microplate reader. To compensate for artifactual fluorescence changes caused by serum color, parallel samples are prepared with excess unlabeled apotransferrin, which scavenges all iron in the sample. Sera from eight hemochromatosis patients were tested for NTBI by the present assay and by an established alternative method, with qualitatively similar results. A potential application of the test is for screening large numbers of samples from patients at risk of developing NTBI.
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Affiliation(s)
- W Breuer
- Department of Biological Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel
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24
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Nagaoka MH, Maitani T. Effects of sialic acid residues of transferrin on the binding with aluminum and iron studied by HPLC/high-resolution ICP-MS. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1526:175-82. [PMID: 11325539 DOI: 10.1016/s0304-4165(01)00124-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Transferrins (Tfs) are glycoproteins with carbohydrate chains in the C-lobe. Carbohydrate-deficient Tfs (CDTs) with fewer sialic acids increased in several diseases. In this study, the affinity of metals (Al and Fe) to Tfs was compared between native- and asialo-Tf by on-line high-performance liquid chromatography/high-resolution inductively coupled plasma mass spectrometry, to clarify whether the presence of sialic acids influences the metal binding. Fe added as Fe-citrate in the presence of bicarbonate preferred the N-lobe site and the binding affinity was similar between native- and asialo-Tfs. Al-citrate added at Al/Tf = 1 also preferred the N-lobe site, while the binding affinity was higher to asialo-Tf than to native-Tf. In Al-oxalate addition, the affinity to the N-lobe site of both Tfs increased further. In the absence of bicarbonate, Al-oxalate showed a preference for the C-lobe site in native-Tf and comparable affinity to both lobes in asialo-Tf. In asialo-Tf, Al2-Tf was the largest peak even at Al/Tf = 1. Thus, the lack of sialic acid in glycans and the presence of oxalate enhanced the binding affinity of Al to Tf. Therefore, it was suggested that the binding affinity of Al in patients with CDTs may be enhanced.
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Affiliation(s)
- M H Nagaoka
- National Institute of Health Sciences, Kamiyoga 1-18-1, Setagaya, 158-8501, Tokyo, Japan
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25
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He QY, Mason AB, Lyons BA, Tam BM, Nguyen V, MacGillivray RT, Woodworth RC. Spectral and metal-binding properties of three single-point tryptophan mutants of the human transferrin N-lobe. Biochem J 2001; 354:423-9. [PMID: 11171122 PMCID: PMC1221671 DOI: 10.1042/0264-6021:3540423] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Human serum transferrin N-lobe (hTF/2N) contains three conserved tryptophan residues, Trp(8), Trp(128) and Trp(264), located in three different environments. The present report addresses the different contributions of the three tryptophan residues to the UV-visible, fluorescence and NMR spectra of hTF/2N and the effect of the mutations at each tryptophan residue on the iron-binding properties of the protein. Trp(8) resides in a hydrophobic box containing a cluster of three phenylalanine side chains and is H bonded through the indole N to an adjacent water cluster lying between two beta-sheets containing Trp(8) and Lys(296) respectively. The fluorescence of Trp(8) may be quenched by the benzene rings. The apparent increase in the rate of iron release from the Trp(8)-->Tyr mutant could be due to the interference of the mutation with the H-bond linkage resulting in an effect on the second shell network. The partial quenching in the fluorescence of Trp(128) results from the nearby His(119) residue. Difference-fluorescence spectra reveal that any protein containing Trp(128) shows a blue shift upon binding metal ion, and the NMR signal of Trp(128) broadens out and disappears upon the binding of paramagnetic metals to the protein. These data imply that Trp(128) is a major fluorescent and NMR reporter group for metal binding, and possibly for cleft closure in hTF/2N. Trp(264) is located on the surface of the protein and does not connect to any functional residues. This explains the facts that Trp(264) is the major contributor to both the absorbance and fluorescence spectra, has a strong NMR signal and the mutation at Trp(264) has little effect on the iron-binding and release behaviours of the protein.
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Affiliation(s)
- Q Y He
- Department of Biochemistry, College of Medicine, University of Vermont, Burlington, VT 05405, U.S.A.
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26
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Metzler DE, Metzler CM, Sauke DJ. Transition Metals in Catalysis and Electron Transport. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50019-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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27
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Affiliation(s)
- H Sun
- Department of Chemistry, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JJ, U.K., and Department of Chemistry, the University of Hong Kong, Pokfulam Road, Hong Kong SAR, China
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28
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He QY, Mason AB, Woodworth RC, Tam BM, MacGillivray RT, Grady JK, Chasteen ND. Mutations at nonliganding residues Tyr-85 and Glu-83 in the N-lobe of human serum transferrin. Functional second shell effects. J Biol Chem 1998; 273:17018-24. [PMID: 9642266 DOI: 10.1074/jbc.273.27.17018] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The x-ray crystal structure of the N-lobe of human serum transferrin has shown that there is a hydrogen bond network, the so-called "second shell," around the transferrin iron binding site. Tyrosine at position 85 and glutamic acid at position 83 are two nonliganding residues in this network in the human serum transferrin N-lobe (hTF/2N). Mutation of each of these two amino acids has a profound effect on the metal binding properties of hTF/2N. When Tyr-85 is mutated to phenylalanine, iron release from the resulting mutant Y85F is much more facile than from the parent protein. Elimination of the hydrogen bond between Tyr-85 and Lys-296 appears to interfere with the "di-lysine (Lys-206-Lys-296) trigger," which affects the iron binding stability of the protein. Surprisingly, mutation of Glu-83 to alanine leads to the absence of one of the normal iron binding ligands; introduction of a monovalent anion is able to restore the normal first coordination sphere. The missing ligand appears to be His-249, as revealed by comparison of the metal binding behaviors of mutants H249Q and E83A and structural analysis. Glu-83 has a strong H bond linkage with His-249 in apo-hTF/2N, which helps to hold the His-249 in the proper position for iron binding. Disabling Glu-83 by mutation to an alanine seriously disturbs the H bond network, allowing His-249 to move away. A monovalent anion can help reestablish the normal network by providing a negative charge near the position of Glu-83 to reach charge balance, so that ligand His-249 is available again for iron binding.
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Affiliation(s)
- Q Y He
- Department of Biochemistry, College of Medicine, University of Vermont, Burlington, Vermont 05405.
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29
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30
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Kawabata T, Ma Y, Okada S. ESR Study of Iron(III) inN-Terminal Lobe of Hen Ovotransferrin. CHEM LETT 1997. [DOI: 10.1246/cl.1997.1195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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31
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Maguire BC, Gaffney BJ. Interdoublet transitions in S = 5/2 protein systems. SOLID STATE NUCLEAR MAGNETIC RESONANCE 1997; 9:81-83. [PMID: 9413907 DOI: 10.1016/s0926-2040(97)00047-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Beginning with known parameters that characterize the EMR spectra of several proteins containing high-spin ferric iron, the information content of the spectra has been examined by simulations that cover a range of magnetic fields and frequencies. Transitions between levels that are not Kramers doublet levels are particularly interesting when the applied frequency is approximately two to three times the value of the zero-field splitting parameter, D. In these cases, transitions at very low magnetic fields correspond to portions of interdoublet transitions that are well separated from all other transitions. The magnetic field is aligned at angles between the molecular principal axes for the portion of the molecules giving rise to the low-field interdoublet transitions. This provides an opportunity for unique angle-selection experiments.
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Affiliation(s)
- B C Maguire
- National High Magnetic Field Laboratory, Florida State University, Tallahassee 32306, USA
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32
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Sun H, Cox MC, Li H, Sadler PJ. Rationalisation of metal binding to transferrin: Prediction of metal-protein stability constants. METAL SITES IN PROTEINS AND MODELS 1997. [DOI: 10.1007/3-540-62870-3_3] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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