351
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Dassler K, Zydek M, Wandzik K, Kaup M, Fuchs H. Release of the Soluble Transferrin Receptor Is Directly Regulated by Binding of Its Ligand Ferritransferrin. J Biol Chem 2006; 281:3297-304. [PMID: 16354665 DOI: 10.1074/jbc.m511341200] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human transferrin receptor (TfR) is shed by an integral metalloprotease releasing a soluble form (sTfR) into serum. The sTfR reflects the iron demand of the body and is postulated as a regulator of iron homeostasis via binding to the hereditary hemochromatosis protein HFE. To study the role of transferrin in this process, we investigated TfR shedding in HL60 cells and TfR-deficient Chinese hamster ovary cells transfected with human TfR. Independent of TfR expression, sTfR release decreases with increasing ferritransferrin concentrations, whereas apo-transferrin exhibits no inhibitory effect. To investigate the underlying mechanism, we generated several TfR mutants with different binding affinities for transferrin. Shedding of TfR mutants in transfected cells correlates exactly with their binding affinity, implying that the effect of ferritransferrin on TfR shedding is mediated by a direct molecular interaction. Analysis of sTfR release from purified microsomal membranes revealed that the regulation is independent from intracellular trafficking or cellular signaling events. Our results clearly demonstrated that sTfR does not only reflect the iron demand of the cells but also the iron availability in the bloodstream, mirrored by iron saturation of transferrin, corroborating the important potential function of sTfR as a regulator of iron homeostasis.
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Affiliation(s)
- Katrin Dassler
- Institut für Klinische Chemie und Pathobiochemie, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin 12200, Germany
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352
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Teh EM, Hewitt J, Ung KC, Griffiths TAM, Nguyen V, Briggs SK, Mason AB, MacGillivray RTA. Identification of the epitope of a monoclonal antibody that disrupts binding of human transferrin to the human transferrin receptor. FEBS J 2006; 272:6344-53. [PMID: 16336271 DOI: 10.1111/j.1742-4658.2005.05028.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The molecular basis of the transferrin (TF)-transferrin receptor (TFR) interaction is not known. The C-lobe of TF is required to facilitate binding to the TFR and both the N- and C-lobes are necessary for maximal binding. Several mAb have been raised against human transferrin (hTF). One of these, designated F11, is specific to the C-lobe of hTF and does not recognize mouse or pig TF. Furthermore, mAb F11 inhibits the binding of TF to TFR on HeLa cells. To map the epitope for mAb F11, constructs spanning various regions of hTF were expressed as glutathione S-transferase (GST) fusion proteins in Escherichia coli. The recombinant fusion proteins were analysed in an iterative fashion by immunoblotting using mAb F11 as the probe. This process resulted in the localization of the F11 epitope to the C1 domain (residues 365-401) of hTF. Subsequent computer modelling suggested that the epitope is probably restricted to a surface patch of hTF consisting of residues 365-385. Mutagenesis of the F11 epitope of hTF to the sequence of either mouse or pig TF confirmed the identity of the epitope as immunoreactivity was diminished or lost. In agreement with other studies, these epitope mapping studies support a role for residues in the C1 domain of hTF in receptor binding.
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Affiliation(s)
- Evelyn M Teh
- Department of Biochemistry and Molecular Biology and Centre for Blood Research, University of British Columbia, Vancouver, Canada
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353
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Yin J, Lin AJ, Buckett PD, Wessling-Resnick M, Golan DE, Walsh CT. Single-cell FRET imaging of transferrin receptor trafficking dynamics by Sfp-catalyzed, site-specific protein labeling. ACTA ACUST UNITED AC 2006; 12:999-1006. [PMID: 16183024 PMCID: PMC2494879 DOI: 10.1016/j.chembiol.2005.07.006] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2005] [Revised: 06/30/2005] [Accepted: 07/08/2005] [Indexed: 12/24/2022]
Abstract
Fluorescence imaging of living cells depends on an efficient and specific method for labeling the target cellular protein with fluorophores. Here we show that Sfp phosphopantetheinyl transferase-catalyzed protein labeling is suitable for fluorescence imaging of membrane proteins that spend at least part of their membrane trafficking cycle at the cell surface. In this study, transferrin receptor 1 (TfR1) was fused to peptide carrier protein (PCP), and the TfR1-PCP fusion protein was specifically labeled with fluorophore Alexa 488 by Sfp. The trafficking of transferrin-TfR1-PCP complex during the process of transferrin-mediated iron uptake was imaged by fluorescence resonance energy transfer between the fluorescently labeled transferrin ligand and TfR1 receptor. We thus demonstrated that Sfp-catalyzed small molecule labeling of the PCP tag represents a practical and efficient tool for molecular imaging studies in living cells.
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Affiliation(s)
- Jun Yin
- Department of Biological Chemistry and Molecular Pharmacology Harvard Medical School 240 Longwood Avenue Boston, Massachusetts 02115
| | - Alison J. Lin
- Department of Biological Chemistry and Molecular Pharmacology Harvard Medical School 240 Longwood Avenue Boston, Massachusetts 02115
| | - Peter D. Buckett
- Department of Genetics and Complex Diseases Harvard School of Public Health 665 Huntington Avenue Boston, Massachusetts 02115
| | - Marianne Wessling-Resnick
- Department of Genetics and Complex Diseases Harvard School of Public Health 665 Huntington Avenue Boston, Massachusetts 02115
- Correspondence: (M.W.-R.); (D.E.G.); (C.T.W.)
| | - David E. Golan
- Department of Biological Chemistry and Molecular Pharmacology Harvard Medical School 240 Longwood Avenue Boston, Massachusetts 02115
- Correspondence: (M.W.-R.); (D.E.G.); (C.T.W.)
| | - Christopher T. Walsh
- Department of Biological Chemistry and Molecular Pharmacology Harvard Medical School 240 Longwood Avenue Boston, Massachusetts 02115
- Correspondence: (M.W.-R.); (D.E.G.); (C.T.W.)
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354
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Schranzhofer M, Schifrer M, Cabrera JA, Kopp S, Chiba P, Beug H, Müllner EW. Remodeling the regulation of iron metabolism during erythroid differentiation to ensure efficient heme biosynthesis. Blood 2006; 107:4159-67. [PMID: 16424395 DOI: 10.1182/blood-2005-05-1809] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Terminal erythropoiesis is accompanied by extreme demand for iron to ensure proper hemoglobinization. Thus, erythroblasts must modify the "standard" post-transcriptional feedback regulation, balancing expression of ferritin (Fer; iron storage) versus transferrin receptor (TfR1; iron uptake) via specific mRNA binding of iron regulatory proteins (IRPs). Although erythroid differentiation involves high levels of incoming iron, TfR1 mRNA stability must be sustained and Fer mRNA translation must not be activated because iron storage would counteract hemoglobinization. Furthermore, translation of the erythroid-specific form of aminolevulinic acid synthase (ALAS-E) mRNA, catalyzing the first step of heme biosynthesis and regulated similarly as Fer mRNA by IRPs, must be ensured. We addressed these questions using mass cultures of primary murine erythroid progenitors from fetal liver, either undergoing sustained proliferation or highly synchronous differentiation. We indeed observed strong inhibition of Fer mRNA translation and efficient ALAS-E mRNA translation in differentiating erythroblasts. Moreover, in contrast to self-renewing cells, TfR1 stability and IRP mRNA binding were no longer modulated by iron supply. These and additional data stemming from inhibition of heme synthesis with succinylacetone or from iron overload suggest that highly efficient utilization of iron in mitochondrial heme synthesis during normal erythropoiesis alters the regulation of iron metabolism via the IRE/IRP system.
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Affiliation(s)
- Matthias Schranzhofer
- Department of Medical Biochemistry, Division of Molecular Biology, Max F. Perutz Laboratories, University Departments at the Vienna Biocenter, Medical University of Vienna, Dr Bohr-Gasse 9, A-1030 Vienna, Austria
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355
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Kalinowski DS, Richardson DR. The Evolution of Iron Chelators for the Treatment of Iron Overload Disease and Cancer. Pharmacol Rev 2005; 57:547-83. [PMID: 16382108 DOI: 10.1124/pr.57.4.2] [Citation(s) in RCA: 554] [Impact Index Per Article: 29.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The evolution of iron chelators from a range of primordial siderophores and aromatic heterocyclic ligands has lead to the formation of a new generation of potent and efficient iron chelators. For example, various siderophore analogs and synthetic ligands, including ICL670A [4-[3,5-bis-(hydroxyphenyl)-1,2,4-triazol-1-yl]-benzoic acid], 4'-hydroxydesazadesferrithiocin, and Triapine, have been developed from predecessors and illustrate potent iron-mobilizing or antineoplastic activities. This review focuses on the evolution of iron chelators from initial lead compounds through to the development of novel chelating agents, many of which show great potential to be clinically applied in the treatment of iron overload disease and cancer.
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Affiliation(s)
- Danuta S Kalinowski
- The Iron Metabolism and Chelation Program, Children's Cancer Institute Australia for Medical Research, Sydney, New South Wales, Australia
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356
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Brown CK, Gu ZY, Matsuka YV, Purushothaman SS, Winter LA, Cleary PP, Olmsted SB, Ohlendorf DH, Earhart CA. Structure of the streptococcal cell wall C5a peptidase. Proc Natl Acad Sci U S A 2005; 102:18391-6. [PMID: 16344483 PMCID: PMC1317908 DOI: 10.1073/pnas.0504954102] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2005] [Indexed: 11/18/2022] Open
Abstract
The structure of a cell surface enzyme from a gram-positive pathogen has been determined to 2-A resolution. Gram-positive pathogens have a thick cell wall to which proteins and carbohydrate are covalently attached. Streptococcal C5a peptidase (SCP), is a highly specific protease and adhesin/invasin. Structural analysis of a 949-residue fragment of the [D130A,S512A] mutant of SCP from group B Streptococcus (S. agalactiae, SCPB) revealed SCPB is composed of five distinct domains. The N-terminal subtilisin-like protease domain has a 134-residue protease-associated domain inserted into a loop between two beta-strands. This domain also contains one of two Arg-Gly-Asp (RGD) sequences found in SCPB. At the C terminus are three fibronectin type III (Fn) domains. The second RGD sequence is located between Fn1 and Fn2. Our analysis suggests that SCP binding to integrins by the RGD motifs may stabilize conformational changes required for substrate binding.
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Affiliation(s)
- C Kent Brown
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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357
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Cheng Y, Zak O, Aisen P, Harrison SC, Walz T. Single particle reconstruction of the human apo-transferrin-transferrin receptor complex. J Struct Biol 2005; 152:204-10. [PMID: 16343946 DOI: 10.1016/j.jsb.2005.10.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2005] [Revised: 10/27/2005] [Accepted: 10/31/2005] [Indexed: 11/19/2022]
Abstract
Most organisms depend on iron as a co-factor for proteins catalyzing redox reactions. Iron is, however, a difficult element for cells to deal with, as it is insoluble in its ferric (Fe3+) form and potentially toxic in its ferrous (Fe2+) form. Thus, in vertebrates iron is transported through the circulation bound to transferrin (Tf) and delivered to cells through an endocytotic cycle involving the transferrin receptor (TfR). We have previously presented a model for the Tf-TfR complex in its iron-bearing form, the diferric transferrin (dTf)-TfR complex [Cheng, Y., Zak, O., Aisen, P., Harrison, S.C., Walz, T., 2004. Structure of the human transferrin receptor-transferrin complex. Cell 116, 565-576]. We have now calculated a single particle reconstruction for the complex in its iron-free form, the apo-transferrin (apoTf)-TfR complex. The same density map was obtained by aligning raw particle images or class averages of the vitrified apoTf-TfR complex to reference models derived from the structures of the dTf-TfR or apoTf-TfR complex. We were unable to improve the resolution of the apoTf-TfR density map beyond 16A, most likely because of significant structural variability of Tf in its iron-free state. The density map does, however, support the model for the apoTf-TfR we previously proposed based on the dTf-TfR complex structure, and it suggests that receptor-bound apoTf prefers to adopt an open conformation.
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Affiliation(s)
- Yifan Cheng
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
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358
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Cheng Y, Wolf E, Larvie M, Zak O, Aisen P, Grigorieff N, Harrison SC, Walz T. Single particle reconstructions of the transferrin-transferrin receptor complex obtained with different specimen preparation techniques. J Mol Biol 2005; 355:1048-65. [PMID: 16343539 DOI: 10.1016/j.jmb.2005.11.021] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2005] [Revised: 10/31/2005] [Accepted: 11/07/2005] [Indexed: 11/24/2022]
Abstract
The outcome of three-dimensional (3D) reconstructions in single particle electron microscopy (EM) depends on a number of parameters. We have used the well-characterized structure of the transferrin (Tf)-transferrin receptor (TfR) complex to study how specimen preparation techniques influence the outcome of single particle EM reconstructions. The Tf-TfR complex is small (290kDa) and of low symmetry (2-fold). Angular reconstitution from images of vitrified specimens does not reliably converge on the correct structure. Random conical tilt reconstructions from negatively stained specimens are reliable, but show variable degrees of artifacts depending on the negative staining protocol. Alignment of class averages from vitrified specimens to a 3D negative stain reference model using FREALIGN largely eliminated artifacts in the resulting 3D maps, but not completely. Our results stress the need for critical evaluation of structures determined by single particle EM.
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Affiliation(s)
- Yifan Cheng
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
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359
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Guan JQ, Chance MR. Structural proteomics of macromolecular assemblies using oxidative footprinting and mass spectrometry. Trends Biochem Sci 2005; 30:583-92. [PMID: 16126388 DOI: 10.1016/j.tibs.2005.08.007] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2005] [Revised: 07/14/2005] [Accepted: 08/16/2005] [Indexed: 11/20/2022]
Abstract
Understanding the composition, structure and dynamics of macromolecules and their assemblies is at the forefront of biological science today. Hydroxyl-radical-mediated protein footprinting using mass spectrometry can define macromolecular structure, macromolecular assembly and conformational changes of macromolecules in solution based on measurements of reactivity of amino acid side-chain groups with covalent-modification reagents. Subsequent to oxidation by reactive oxygen species, proteins are digested by specific proteases to generate peptides for analysis by mass spectrometry. Accurate measurements of side-chain reactivity are achieved using quantitative liquid-chromatography-coupled mass spectrometry, whereas the side-chain sites within the macromolecular probes are identified using tandem mass spectrometry. In addition, the use of footprinting data in conjunction with computational modeling approaches is a powerful new method for testing and refining structural models of macromolecules and their complexes.
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Affiliation(s)
- Jing-Qu Guan
- Case Center for Proteomics and Mass Spectrometry, 930 BRB, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
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360
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Knight SAB, Vilaire G, Lesuisse E, Dancis A. Iron acquisition from transferrin by Candida albicans depends on the reductive pathway. Infect Immun 2005; 73:5482-92. [PMID: 16113264 PMCID: PMC1231083 DOI: 10.1128/iai.73.9.5482-5492.2005] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Host-pathogen interactions that alter virulence are influenced by critical nutrients such as iron. In humans, free iron is unavailable, being present only in high-affinity iron binding proteins such as transferrin. The fungal pathogen Candida albicans grows as a saprophyte on mucosal surfaces. Occasionally it invades systemically, and in this circumstance it will encounter transferrin iron. Here we report that C. albicans is able to acquire iron from transferrin. Iron-loaded transferrin restored growth to cultures arrested by iron deprivation, whereas apotransferrin was unable to promote growth. By using congenic strains, we have been able to show that iron uptake by C. albicans from transferrin was mediated by the reductive pathway (via FTR1). The genetically separate siderophore and heme uptake systems were not involved. FRE10 was required for a surface reductase activity and for efficient transferrin iron uptake activity in unbuffered medium. Other reductase genes were apparently up-regulated in medium buffered at pH 6.3 to 6.4, and the fre10(-/-) mutant had no effect under these conditions. Experiments in which transferrin was sequestered in a dialysis bag demonstrated that cell contact with the substrate was required for iron reduction and release. The requirement of FTR1 for virulence in a systemic infection model and its role in transferrin iron uptake raise the possibility that transferrin is a source of iron during systemic C. albicans infections.
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Affiliation(s)
- Simon A B Knight
- University of Pennsylvania, Department of Medicine, Division of Hematology/Oncology, 731 BRB II/III, 421 Curie Blvd., Philadelphia, PA 19104-6160, USA.
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361
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Jiang W, Ludtke SJ. Electron cryomicroscopy of single particles at subnanometer resolution. Curr Opin Struct Biol 2005; 15:571-7. [PMID: 16140524 DOI: 10.1016/j.sbi.2005.08.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2005] [Revised: 07/09/2005] [Accepted: 08/24/2005] [Indexed: 11/24/2022]
Abstract
Electron cryomicroscopy and single-particle reconstruction have advanced substantially over the past two decades. There are now numerous examples of structures that have been solved using this technique to better than 10 A resolution. At such resolutions, direct identification of alpha helices is possible and, often, beta-sheet-containing regions can be identified. The most numerous subnanometer resolution structures are the icosahedral viruses, as higher resolution is easier to achieve with higher symmetry. Important non-icosahedral structures solved to subnanometer resolution include several ribosome structures, clathrin assemblies and, most recently, the Ca2+ release channel. There is now hope that, in the next few years, this technique will achieve resolutions approaching 4 A, permitting a complete trace of the protein backbone without reference to a crystal structure.
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Affiliation(s)
- Wen Jiang
- National Center for Macromolecular Imaging, Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
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362
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Amanchy R, Kalume DE, Iwahori A, Zhong J, Pandey A. Phosphoproteome Analysis of HeLa Cells Using Stable Isotope Labeling with Amino Acids in Cell Culture (SILAC). J Proteome Res 2005; 4:1661-71. [PMID: 16212419 DOI: 10.1021/pr050134h] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Identification of phosphorylated proteins remains a difficult task despite technological advances in protein purification methods and mass spectrometry. Here, we report identification of tyrosine-phosphorylated proteins by coupling stable isotope labeling with amino acids in cell culture (SILAC) to mass spectrometry. We labeled HeLa cells with stable isotopes of tyrosine, or, a combination of arginine and lysine to identify tyrosine phosphorylated proteins. This allowed identification of 118 proteins, of which only 45 proteins were previously described as tyrosine-phosphorylated proteins. A total of 42 in vivo tyrosine phosphorylation sites were mapped, including 34 novel ones. We validated the phosphorylation status of a subset of novel proteins including cytoskeleton associated protein 1, breast cancer anti-estrogen resistance 3, chromosome 3 open reading frame 6, WW binding protein 2, Nice-4 and RNA binding motif protein 4. Our strategy can be used to identify potential kinase substrates without prior knowledge of the signaling pathways and can also be applied to profiling to specific kinases in cells. Because of its sensitivity and general applicability, our approach will be useful for investigating signaling pathways in a global fashion and for using phosphoproteomics for functional annotation of genomes.
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Affiliation(s)
- Ramars Amanchy
- McKusick-Nathans Institute for Genetic Medicine and the Department of Biological Chemistry and Oncology, Johns Hopkins University, 733 N. Broadway, Baltimore, MD 21205, USA
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363
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Xu G, Liu R, Zak O, Aisen P, Chance MR. Structural allostery and binding of the transferrin*receptor complex. Mol Cell Proteomics 2005; 4:1959-67. [PMID: 16332734 DOI: 10.1074/mcp.m500095-mcp200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The structural allostery and binding interface for the human serum transferrin (Tf)*transferrin receptor (TfR) complex were identified using radiolytic footprinting and mass spectrometry. We have determined previously that the transferrin C-lobe binds to the receptor helical domain. In this study we examined the binding interactions of full-length transferrin with receptor and compared these data with a model of the complex derived from cryoelectron microscopy (cryo-EM) reconstructions (Cheng, Y., Zak, O., Aisen, P., Harrison, S. C. & Walz, T. (2004) Structure of the human transferrin receptor.transferrin complex. Cell 116, 565-576). The footprinting results provide the following novel conclusions. First, we report characteristic oxidations of acidic residues in the C-lobe of native Tf and basic residues in the helical domain of TfR that were suppressed as a function of complex formation; this confirms ionic interactions between these protein segments as predicted by cryo-EM data and demonstrates a novel method for detecting ion pair interactions in the formation of macromolecular complexes. Second, the specific side-chain interactions between the C-lobe and N-lobe of transferrin and the corresponding interactions sites on the transferrin receptor predicted from cryo-EM were confirmed in solution. Last, the footprinting data revealed allosteric movements of the iron binding C- and N-lobes of Tf that sequester iron as a function of complex formation; these structural changes promote tighter binding of the metal ion and facilitate efficient ion transport during endocytosis.
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Affiliation(s)
- Guozhong Xu
- Case Center for Proteomics and Mass Spectrometry, Case Western Reserve University, Cleveland, Ohio 44106, USA
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364
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Xu X, Persson HL, Richardson DR. Molecular pharmacology of the interaction of anthracyclines with iron. Mol Pharmacol 2005; 68:261-71. [PMID: 15883202 DOI: 10.1124/mol.105.013383] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Although anthracyclines such as doxorubicin are widely used antitumor agents, a major limitation for their use is the development of cardiomyopathy at high cumulative doses. This severe adverse side effect may be due to interactions with cellular iron metabolism, because iron loading promotes anthracycline-induced cell damage. On the other hand, anthracycline-induced cardiotoxicity is significantly alleviated by iron chelators (e.g., desferrioxamine and dexrazoxane). The molecular mechanisms by which anthracyclines interfere with cellular iron trafficking are complex and still unclear. Doxorubicin can directly bind iron and can perturb iron metabolism by interacting with multiple molecular targets, including the iron regulatory proteins (IRP) 1 and 2. The RNA-binding activity of these molecules regulates synthesis of the transferrin receptor 1 and ferritin, which are crucial proteins involved in iron uptake and storage, respectively. At present, it is not clear whether doxorubicin affects IRP1-RNA-binding activity by intracellular formation of doxorubicinol and/or by generation of the doxorubicin-iron(III) complex. Furthermore, doxorubicin prevents the mobilization of iron from ferritin by a mechanism that may involve lysosomal degradation of this protein. Prevention of iron mobilization from ferritin would probably disturb vital cellular functions as a result of inhibition of essential iron-dependent proteins, such as ribonucleotide reductase. This review discusses the molecular interactions of anthracyclines with iron metabolism and the development of cardioprotective strategies such as iron chelators.
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Affiliation(s)
- X Xu
- Children's Cancer Institute Australia for Medical Research, Iron Metabolism and Chelation Program, PO Box 81, High St, Randwick, Sydney, New South Wales, 2031 Australia
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365
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Davis MI, Bennett MJ, Thomas LM, Bjorkman PJ. Crystal structure of prostate-specific membrane antigen, a tumor marker and peptidase. Proc Natl Acad Sci U S A 2005; 102:5981-6. [PMID: 15837926 PMCID: PMC556220 DOI: 10.1073/pnas.0502101102] [Citation(s) in RCA: 194] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer cells and nonprostatic solid tumor neovasculature and is a target for anticancer imaging and therapeutic agents. PSMA acts as a glutamate carboxypeptidase (GCPII) on small molecule substrates, including folate, the anticancer drug methotrexate, and the neuropeptide N-acetyl-l-aspartyl-l-glutamate. Here we present the 3.5-A crystal structure of the PSMA ectodomain, which reveals a homodimer with structural similarity to transferrin receptor, a receptor for iron-loaded transferrin that lacks protease activity. Unlike transferrin receptor, the protease domain of PSMA contains a binuclear zinc site, catalytic residues, and a proposed substrate-binding arginine patch. Elucidation of the PSMA structure combined with docking studies and a proposed catalytic mechanism provides insight into the recognition of inhibitors and the natural substrate N-acetyl-l-aspartyl-l-glutamate. The PSMA structure will facilitate development of chemotherapeutics, cancer-imaging agents, and agents for treatment of neurological disorders.
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Affiliation(s)
- Mindy I Davis
- Division of Biology 114-96 and Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, USA
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366
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Yuan JF, Beniac DR, Chaconas G, Ottensmeyer FP. 3D reconstruction of the Mu transposase and the Type 1 transpososome: a structural framework for Mu DNA transposition. Genes Dev 2005; 19:840-52. [PMID: 15774720 PMCID: PMC1074321 DOI: 10.1101/gad.1291405] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Mu DNA transposition proceeds through a series of higher-order nucleoprotein complexes called transpososomes. The structural core of the transpososome is a tetramer of the transposase, Mu A, bound to the two transposon ends. High-resolution structural analysis of the intact transposase and the transpososome has not been successful to date. Here we report the structure of Mu A at 16-angstroms and the Type 1 transpososome at 34-angstroms resolution, by 3D reconstruction of images obtained by scanning transmission electron microscopy (STEM) at cryo-temperatures. Electron spectroscopic imaging (ESI) of the DNA-phosphorus was performed in conjunction with the structural investigation to derive the path of the DNA through the transpososome and to define the DNA-binding surface in the transposase. Our model of the transpososome fits well with the accumulated biochemical literature for this intricate transposition system, and lays a structural foundation for biochemical function, including catalysis in trans and the complex circuit of macromolecular interactions underlying Mu DNA transposition.
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Affiliation(s)
- Joy F Yuan
- Department of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada
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367
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Papanikolaou G, Pantopoulos K. Iron metabolism and toxicity. Toxicol Appl Pharmacol 2005; 202:199-211. [PMID: 15629195 DOI: 10.1016/j.taap.2004.06.021] [Citation(s) in RCA: 564] [Impact Index Per Article: 29.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2004] [Accepted: 06/24/2004] [Indexed: 02/06/2023]
Abstract
Iron is an essential nutrient with limited bioavailability. When present in excess, iron poses a threat to cells and tissues, and therefore iron homeostasis has to be tightly controlled. Iron's toxicity is largely based on its ability to catalyze the generation of radicals, which attack and damage cellular macromolecules and promote cell death and tissue injury. This is lucidly illustrated in diseases of iron overload, such as hereditary hemochromatosis or transfusional siderosis, where excessive iron accumulation results in tissue damage and organ failure. Pathological iron accumulation in the liver has also been linked to the development of hepatocellular cancer. Here we provide a background on the biology and toxicity of iron and the basic concepts of iron homeostasis at the cellular and systemic level. In addition, we provide an overview of the various disorders of iron overload, which are directly linked to iron's toxicity. Finally, we discuss the potential role of iron in malignant transformation and cancer.
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Affiliation(s)
- G Papanikolaou
- First Department of Internal Medicine, National and Kapodistrian University of Athens, School of Medicine, Laikon General Hospital, Athens 11527, Greece
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368
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Napier I, Ponka P, Richardson DR. Iron trafficking in the mitochondrion: novel pathways revealed by disease. Blood 2005; 105:1867-74. [PMID: 15528311 DOI: 10.1182/blood-2004-10-3856] [Citation(s) in RCA: 197] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
It is well known that iron (Fe) is transported to the mitochondrion for heme synthesis. However, only recently has the importance of this organelle for many other facets of Fe metabolism become widely appreciated. Indeed, this was stimulated by the description of human disease states that implicate mitochondrial Fe metabolism. In particular, studies assessing various diseases leading to mitochondrial Fe loading have produced intriguing findings. For instance, the disease X-linked sideroblastic anemia with ataxia (XLSA/A) is due to a mutation in the ATP-binding cassette protein B7 (ABCB7) transporter that is thought to transfer [Fe-S] clusters from the mitochondrion to the cytoplasm. This and numerous other findings suggest the mitochondrion is a dynamo of Fe metabolism, being vital not only for heme synthesis but also for playing a critical role in the genesis of [Fe-S] clusters. Studies examining the disease Friedreich ataxia have suggested that a mutation in the gene encoding frataxin leads to mitochondrial Fe loading. Apart from these findings, the recently discovered mitochondrial ferritin that may store Fe in ring sideroblasts could also regulate the level of Fe needed for heme and [Fe-S] cluster synthesis. In this review, we suggest a model of mitochondrial Fe processing that may account for the pathology observed in these disease states.
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Affiliation(s)
- Ian Napier
- Children's Cancer Institute Australia for Medical Research, Iron Metabolism and Chelation Program, PO Box 81, High St, Randwick, Sydney, New South Wales, 2031 Australia
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369
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Wingert RA, Brownlie A, Galloway JL, Dooley K, Fraenkel P, Axe JL, Davidson AJ, Barut B, Noriega L, Sheng X, Zhou Y, Zon LI. The chianti zebrafish mutant provides a model for erythroid-specific disruption of transferrin receptor 1. Development 2005; 131:6225-35. [PMID: 15563524 DOI: 10.1242/dev.01540] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Iron is a crucial metal for normal development, being required for the production of heme, which is incorporated into cytochromes and hemoglobin. The zebrafish chianti (cia) mutant manifests a hypochromic, microcytic anemia after the onset of embryonic circulation, indicative of a perturbation in red blood cell hemoglobin production. We show that cia encodes tfr1a, which is specifically expressed in the developing blood and requisite only for iron uptake in erythroid precursors. In the process of isolating zebrafish tfr1, we discovered two tfr1-like genes (tfr1a and tfr1b) and a single tfr2 ortholog. Abrogation of tfr1b function using antisense morpholinos revealed that this paralog was dispensable for hemoglobin production in red cells. tfr1b morphants exhibited growth retardation and brain necrosis, similar to the central nervous system defects observed in the Tfr1 null mouse, indicating that tfr1b is probably used by non-erythroid tissues for iron acquisition. Overexpression of mouse Tfr1, mouse Tfr2, and zebrafish tfr1b partially rescued hypochromia in cia embryos, establishing that each of these transferrin receptors are capable of supporting iron uptake for hemoglobin production in vivo. Taken together, these data show that zebrafish tfr1a and tfr1b share biochemical function but have restricted domains of tissue expression, and establish a genetic model to study the specific function of Tfr1 in erythroid cells.
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Affiliation(s)
- Rebecca A Wingert
- Department of Hematology/Oncology, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA
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370
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Creagh AL, Tiong JWC, Tian MM, Haynes CA, Jefferies WA. Calorimetric studies of melanotransferrin (p97) and its interaction with iron. J Biol Chem 2005; 280:15735-41. [PMID: 15705575 DOI: 10.1074/jbc.m414650200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mammalian molecule melanotransferrin (mTf), also called p97, is a member of the transferrin family of molecules. It exists in both secreted and glycosylphosphatidylinositol-anchored forms and is thought to play a role in angiogenesis and in transporting iron across the blood brain barrier. The binding affinity of iron to this molecule has not been formally established. Here, the binding of ferric ion (chelated with a 2-fold molar ratio of nitrilotriacetate) to mTf has been studied using isothermal titration calorimetry and differential scanning calorimetry. One iron-binding site was determined for mTf with similar binding characteristics to other transferrins. In the absence of bicarbonate, binding occurs quickly with an apparent association constant of 2.6 x 10(7) M(-1) at 25 degrees C. The presence of bicarbonate introduces kinetic effects that prevent direct determination of the apparent binding constant by isothermal titration calorimetry. Differential scanning calorimetry thermograms of mTf unfolding in the presence and absence of iron were therefore used to determine the apparent binding constant in the bicarbonate-containing system; at pH 7.5 and 25 degrees C, iron binding occurs in a 1:1 ratio with a K(app) of 4.4 x 10(17) M(-1). This affinity is intermediate between the high and low affinity lobes of transferrin and suggests that mTf is likely to play a significant role in iron transport where the high affinity lobe of transferrin is occupied or where transferrin is in proportionally low concentrations.
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Affiliation(s)
- A Louise Creagh
- Michael Smith Laboratories and Biomedical Research Centre, Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
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371
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Mason AB, Halbrooks PJ, Larouche JR, Briggs SK, Moffett ML, Ramsey JE, Connolly SA, Smith VC, MacGillivray RTA. Expression, purification, and characterization of authentic monoferric and apo-human serum transferrins. Protein Expr Purif 2005; 36:318-26. [PMID: 15249056 DOI: 10.1016/j.pep.2004.04.013] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2004] [Revised: 04/12/2004] [Indexed: 11/17/2022]
Abstract
Transferrin is a bilobal protein with the ability to bind iron in two binding sites situated at the bottom of a cleft in each lobe. We have previously described the production of recombinant non-glycosylated human serum transferrins (hTF-NG), containing a factor Xa cleavage site and a hexa-His tag at the amino-terminus. Constructs in this background that contain strategic mutations to completely prevent iron binding in each lobe or in both lobes have now been produced. These monoferric hTFs will allow dissection of the contribution of each lobe to transferrin function. In addition, the construct completely lacking in the ability to bind iron in either lobe provides an opportunity to assess whether hTF has any other functions in addition to iron transport. Following insertion of the His-tagged hTF molecules into the pNUT vector, transfection into baby hamster kidney cells and selection with methotrexate, the secreted recombinant proteins were isolated from the tissue culture medium and characterized with regard to their iron binding properties. Significant improvements over our previous protocol include: (1) addition of butyric acid at a level of 1mM which leads to a substantial increase in protein production (as much as a 65% increase compared to control cells); and (2) elimination of an anion exchange column prior to isolation on a Qiagen Ni-NTA column which makes purification of the His-tagged constructs faster and therefore more efficient. These improvements should be applicable to expression of other recombinant proteins in mammalian cells.
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Affiliation(s)
- Anne B Mason
- Department of Biochemistry, University of Vermont, College of Medicine, 89 Beaumont Avenue, Burlington, VT 05405, USA.
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372
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Stewart A, Grigorieff N. Noise bias in the refinement of structures derived from single particles. Ultramicroscopy 2005; 102:67-84. [PMID: 15556702 DOI: 10.1016/j.ultramic.2004.08.008] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2004] [Revised: 08/14/2004] [Accepted: 08/24/2004] [Indexed: 10/26/2022]
Abstract
One of the main goals in the determination of three-dimensional macromolecular structures from electron microscope images of individual molecules and complexes (single particles) is a sufficiently high spatial resolution, about 4 A, at which the interpretation with an atomic model becomes possible. To reach high resolution, an iterative refinement procedure using an expectation maximization algorithm is often used that leads to a more accurate alignment of the positional and orientational parameters for each particle. We show here the results of refinement algorithms that use a phase residual, a linear correlation coefficient, or a weighted correlation coefficient to align individual particles. The algorithms were applied to computer-generated data sets that contained projections from model structures, as well as noise. The algorithms show different degrees of over-fitting, especially at high resolution where the signal is weak. We demonstrate that the degree of over-fitting is reduced with a weighting scheme that depends on the signal-to-noise ratio in the data. The weighting also improves the accuracy of resolution measurement by the commonly used Fourier shell correlation. The performance of the refinement algorithms is compared to that using a maximum likelihood approach. The weighted correlation coefficient was implemented in the computer program FREALIGN.
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Affiliation(s)
- Alex Stewart
- Howard Hughes Medical Institute and Department of Biochemistry, Rosenstiel Basic Medical Sciences Research Center, MS029, Brandeis University, 415 South Street, Waltham, MA 02454-9110, USA
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373
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Aisen P. Transferrin receptor 1. Int J Biochem Cell Biol 2004; 36:2137-43. [PMID: 15313461 DOI: 10.1016/j.biocel.2004.02.007] [Citation(s) in RCA: 206] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2004] [Revised: 02/03/2004] [Accepted: 02/03/2004] [Indexed: 11/17/2022]
Abstract
With the discovery that transferrin serves as the iron source for hemoglobin-synthesizing immature red blood cells came the demonstration that a cell surface receptor, now known as transferrin receptor 1, is required for iron delivery from transferrin to cells. (A recently described second transferrin receptor, with as yet poorly understood function, will not be discussed in this brief review.) In succeeding years transferrin receptor 1 was established as a gatekeeper for regulating iron uptake by most cells, and the transferrin-to-cell endocytic pathway characterized in detail. HFE, the protein incriminated in the pathogenesis of hereditary hemochromatosis, a disorder of progressive and toxic iron overload, competes with transferrin for binding to receptor, thereby impeding the uptake of iron from transferrin. Mutation of HFE destroys this competition, thus facilitating access of transferrin and its iron to cells. Availability of the crystal structure of transferrin receptor 1, along with those of transferrin and HFE, opened research on molecular mapping of the transferrin-HFE- transferrin receptor interfaces by correlated synchrotron-generated hydroxyl radical footprinting and cryo-electron microscopy. The emerging challenge is to relate structure to the functional effects of receptor binding on the iron-binding and iron-releasing properties of transferrin within the iron-dependent cell.
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Affiliation(s)
- Philip Aisen
- Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
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374
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Orlova EV, Saibil HR. Structure determination of macromolecular assemblies by single-particle analysis of cryo-electron micrographs. Curr Opin Struct Biol 2004; 14:584-90. [PMID: 15465319 DOI: 10.1016/j.sbi.2004.08.004] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
A new generation of electron microscopes equipped with field emission gun electron sources and the ability to image molecules in their native environment at liquid nitrogen or helium temperatures has enabled the analysis of macromolecular structures at medium resolution (approximately 10 angstroms) and in different conformational states. The amalgamation of electron microscopy and X-ray crystallographic approaches makes it possible to solve structures in the 100-1000 angstroms size range, advancing our understanding of the function of complex assemblies. Many new structures have been solved during the past two years, including one of the smallest complexes to be determined by single-particle cryo-electron microscopy, the transferrin receptor-transferrin complex. Other notable results include the near atomic level resolution structure of the nicotinic acetylcholine receptor in helical arrays and an icosahedral virus structure with an asymmetric polymerase resolved.
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Affiliation(s)
- Elena V Orlova
- School of Crystallography, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK
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375
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Abstract
Iron is ubiquitous in the environment and in biology. The study of iron biology focuses on physiology and homeostasis-understanding how cells and organisms regulate their iron content, how diverse tissues orchestrate iron allocation, and how dysregulated iron homeostasis leads to common hematological, metabolic, and neurodegenerative diseases. This has provided novel insights into gene regulation and unveiled remarkable links to the immune system.
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Affiliation(s)
- Matthias W Hentze
- European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany.
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376
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Abstract
How does the iron (Fe) binding protein, transferrin (Tf), bind to the transferrin receptor 1 (TfR1) to donate Fe to cells? In this issue of Cell, Cheng et al., describe the molecular structure of the human TfR1-Tf complex, This atomic model shows that Tf binds laterally to the TfR1 dimer and extends into the gap between the bottom of the receptor ectodomain and the membrane.
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Affiliation(s)
- D R Richardson
- Children's Cancer Institute Australia for Medical Research, The Iron Metabolism and Chelation Program, PO Box 81, High Street, Randwick, Sydney, New South Wales 2031, Australia
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377
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Giannetti AM, Björkman PJ. HFE and transferrin directly compete for transferrin receptor in solution and at the cell surface. J Biol Chem 2004; 279:25866-75. [PMID: 15056661 DOI: 10.1074/jbc.m401467200] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Transferrin receptor (TfR) is a dimeric cell surface protein that binds both the serum iron transport protein transferrin (Fe-Tf) and HFE, the protein mutated in patients with the iron overload disorder hereditary hemochromatosis. HFE and Fe-Tf can bind simultaneously to TfR to form a ternary complex, but HFE binding to TfR lowers the apparent affinity of the Fe-Tf/TfR interaction. This apparent affinity reduction could result from direct competition between HFE and Fe-Tf for their overlapping binding sites on each TfR polypeptide chain, from negative cooperativity, or from a combination of both. To explore the mechanism of the affinity reduction, we constructed a heterodimeric TfR that contains mutations such that one TfR chain binds only HFE and the other binds only Fe-Tf. Binding studies using a heterodimeric form of soluble TfR demonstrate that TfR does not exhibit cooperativity in heterotropic ligand binding, suggesting that some or all of the effects of HFE on iron homeostasis result from competition with Fe-Tf for TfR binding. Experiments using transfected cell lines demonstrate a physiological role for this competition in altering HFE trafficking patterns.
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Affiliation(s)
- Anthony M Giannetti
- Graduate Option in Biochemistry and Molecular Biophysics, California Institute of Technology, Pasadena, CA 91125, USA
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378
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Ohi M, Li Y, Cheng Y, Walz T. Negative Staining and Image Classification - Powerful Tools in Modern Electron Microscopy. Biol Proced Online 2004; 6:23-34. [PMID: 15103397 PMCID: PMC389902 DOI: 10.1251/bpo70] [Citation(s) in RCA: 539] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2004] [Revised: 03/09/2004] [Accepted: 03/09/2004] [Indexed: 11/23/2022] Open
Abstract
Vitrification is the state-of-the-art specimen preparation technique for molecular electron microscopy (EM) and therefore negative staining may appear to be an outdated approach. In this paper we illustrate the specific advantages of negative staining, ensuring that this technique will remain an important tool for the study of biological macromolecules. Due to the higher image contrast, much smaller molecules can be visualized by negative staining. Also, while molecules prepared by vitrification usually adopt random orientations in the amorphous ice layer, negative staining tends to induce preferred orientations of the molecules on the carbon support film. Combining negative staining with image classification techniques makes it possible to work with very heterogeneous molecule populations, which are difficult or even impossible to analyze using vitrified specimens.
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Affiliation(s)
- Melanie Ohi
- Department of Cell Biology, Harvard Medical School. 240 Longwood Avenue, Boston, MA, 02115. USA
| | - Ying Li
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School. 240 Longwood Avenue, Boston, MA, 02115. USA
| | - Yifan Cheng
- Department of Cell Biology, Harvard Medical School. 240 Longwood Avenue, Boston, MA, 02115. USA
| | - Thomas Walz
- Department of Cell Biology, Harvard Medical School. 240 Longwood Avenue, Boston, MA, 02115. USA
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