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Mucha P, Kus F, Cysewski D, Smolenski RT, Tomczyk M. Vitamin B 12 Metabolism: A Network of Multi-Protein Mediated Processes. Int J Mol Sci 2024; 25:8021. [PMID: 39125597 PMCID: PMC11311337 DOI: 10.3390/ijms25158021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2024] [Revised: 07/12/2024] [Accepted: 07/19/2024] [Indexed: 08/12/2024] Open
Abstract
The water-soluble vitamin, vitamin B12, also known as cobalamin, plays a crucial role in cellular metabolism, particularly in DNA synthesis, methylation, and mitochondrial functionality. Its deficiency can lead to hematological and neurological disorders; however, the manifestation of these clinical outcomes is relatively late. It leads to difficulties in the early diagnosis of vitamin B12 deficiency. A prolonged lack of vitamin B12 may have severe consequences including increased morbidity to neurological and cardiovascular diseases. Beyond inadequate dietary intake, vitamin B12 deficiency might be caused by insufficient bioavailability, blood transport disruptions, or impaired cellular uptake and metabolism. Despite nearly 70 years of knowledge since the isolation and characterization of this vitamin, there are still gaps in understanding its metabolic pathways. Thus, this review aims to compile current knowledge about the crucial proteins necessary to efficiently accumulate and process vitamin B12 in humans, presenting these systems as a multi-protein network. The epidemiological consequences, diagnosis, and treatment of vitamin B12 deficiency are also highlighted. We also discuss clinical warnings of vitamin B12 deficiency based on the ongoing test of specific moonlighting proteins engaged in vitamin B12 metabolic pathways.
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Affiliation(s)
- Patryk Mucha
- Department of Biochemistry, Medical University of Gdansk, 80-210 Gdansk, Poland; (P.M.); (F.K.); (R.T.S.)
| | - Filip Kus
- Department of Biochemistry, Medical University of Gdansk, 80-210 Gdansk, Poland; (P.M.); (F.K.); (R.T.S.)
- Laboratory of Protein Biochemistry, Intercollegiate Faculty of Biotechnology of University of Gdansk and Medical University of Gdansk, 80-307 Gdansk, Poland
| | - Dominik Cysewski
- Clinical Research Centre, Medical University of Bialystok, 15-276 Bialystok, Poland;
| | - Ryszard T. Smolenski
- Department of Biochemistry, Medical University of Gdansk, 80-210 Gdansk, Poland; (P.M.); (F.K.); (R.T.S.)
| | - Marta Tomczyk
- Department of Biochemistry, Medical University of Gdansk, 80-210 Gdansk, Poland; (P.M.); (F.K.); (R.T.S.)
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2
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Bokhove M, Kawamura T, Okumura H, Goto S, Kawano Y, Werner S, Jarczowski F, Klimyuk V, Saito A, Kumasaka T. The structure of the rat vitamin B 12 transporter TC and its complex with glutathionylcobalamin. J Biol Chem 2024; 300:107289. [PMID: 38636663 PMCID: PMC11107200 DOI: 10.1016/j.jbc.2024.107289] [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: 12/21/2023] [Revised: 04/07/2024] [Accepted: 04/09/2024] [Indexed: 04/20/2024] Open
Abstract
Vitamin B12 (cobalamin or Cbl) functions as a cofactor in two important enzymatic processes in human cells, and life is not sustainable without it. B12 is obtained from food and travels from the stomach, through the intestine, and into the bloodstream by three B12-transporting proteins: salivary haptocorrin (HC), gastric intrinsic factor, and transcobalamin (TC), which all bind B12 with high affinity and require proteolytic degradation to liberate Cbl. After intracellular delivery of dietary B12, Cbl in the aquo/hydroxocobalamin form can coordinate various nucleophiles, for example, GSH, giving rise to glutathionylcobalamin (GSCbl), a naturally occurring form of vitamin B12. Currently, there is no data showing whether GSCbl is recognized and transported in the human body. Our crystallographic data shows for the first time the complex between a vitamin B12 transporter and GSCbl, which compared to aquo/hydroxocobalamin, binds TC equally well. Furthermore, sequence analysis and structural comparisons show that TC recognizes and transports GSCbl and that the residues involved are conserved among TCs from different organisms. Interestingly, haptocorrin and intrinsic factor are not structurally tailored to bind GSCbl. This study provides new insights into the interactions between TC and Cbl.
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Affiliation(s)
- Marcel Bokhove
- Structural Biology Division, Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo, Japan.
| | - Takashi Kawamura
- Structural Biology Division, Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo, Japan
| | - Hideo Okumura
- Structural Biology Division, Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo, Japan
| | - Sawako Goto
- Department of Applied Molecular Medicine, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Japan
| | - Yoshiaki Kawano
- Advanced Photon Technology Division, RIKEN SPring-8 Center, Sayo, Hyogo, Japan
| | | | | | | | - Akihiko Saito
- Department of Applied Molecular Medicine, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Japan
| | - Takashi Kumasaka
- Structural Biology Division, Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo, Japan.
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3
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McCorvie TJ, Ferreira D, Yue WW, Froese DS. The complex machinery of human cobalamin metabolism. J Inherit Metab Dis 2023; 46:406-420. [PMID: 36680553 DOI: 10.1002/jimd.12593] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Revised: 01/17/2023] [Accepted: 01/19/2023] [Indexed: 01/22/2023]
Abstract
Vitamin B12 (cobalamin, Cbl) is required as a cofactor by two human enzymes, 5-methyltetrahydrofolate-homocysteine methyltransferase (MTR) and methylmalonyl-CoA mutase (MMUT). Within the body, a vast array of transporters, enzymes and chaperones are required for the generation and delivery of these cofactor forms. How they perform these functions is dictated by the structure and interactions of the proteins involved, the molecular bases of which are only now being elucidated. In this review, we highlight recent insights into human Cbl metabolism and address open questions in the field by employing a protein structure and interactome based perspective. We discuss how three very similar proteins-haptocorrin, intrinsic factor and transcobalamin-exploit slight structural differences and unique ligand receptor interactions to effect selective Cbl absorption and internalisation. We describe recent advances in the understanding of how endocytosed Cbl is transported across the lysosomal membrane and the implications of the recently solved ABCD4 structure. We detail how MMACHC and MMADHC cooperate to modify and target cytosolic Cbl to the client enzymes MTR and MMUT using ingenious modifications to an ancient nitroreductase fold, and how MTR and MMUT link with their accessory enzymes to sustainably harness the supernucleophilic potential of Cbl. Finally, we provide an outlook on how future studies may combine structural and interactome based approaches and incorporate knowledge of post-translational modifications to bring further insights.
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Affiliation(s)
- Thomas J McCorvie
- Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, UK
| | - Douglas Ferreira
- Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, UK
- Centre for Medicines Discovery, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Wyatt W Yue
- Biosciences Institute, The Medical School, Newcastle University, Newcastle upon Tyne, UK
| | - D Sean Froese
- Division of Metabolism and Children's Research Center, University Children's Hospital Zürich, University of Zürich, Zürich, Switzerland
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4
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Kozyraki R, Verroust P, Cases O. Cubilin, the intrinsic factor-vitamin B12 receptor. VITAMINS AND HORMONES 2022; 119:65-119. [PMID: 35337634 DOI: 10.1016/bs.vh.2022.01.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Cubilin (CUBN), the intrinsic factor-vitamin B12 receptor is a large endocytic protein involved in various physiological functions: vitamin B12 uptake in the gut; reabsorption of albumin and maturation of vitamin D in the kidney; nutrient delivery during embryonic development. Cubilin is an atypical receptor, peripherally associated to the plasma membrane. The transmembrane proteins amnionless (AMN) and Lrp2/Megalin are the currently known molecular partners contributing to plasma membrane transport and internalization of Cubilin. The role of Cubilin/Amn complex in the handling of vitamin B12 in health and disease has extensively been studied and so is the role of the Cubilin-Lrp2 tandem in renal pathophysiology. Accumulating evidence strongly supports a role of Cubilin in some developmental defects including impaired closure of the neural tube. Are these defects primarily caused by the dysfunction of a specific Cubilin ligand or are they secondary to impaired vitamin B12 or protein uptake? We will present the established Cubilin functions, discuss the developmental data and provide an overview of the emerging implications of Cubilin in the field of cardiovascular disease and cancer pathogenesis.
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Affiliation(s)
- Renata Kozyraki
- Centre de Recherche des Cordeliers, Sorbonne Université, INSERM, Université de Paris, Paris, France.
| | - Pierre Verroust
- Centre de Recherche des Cordeliers, Sorbonne Université, INSERM, Université de Paris, Paris, France
| | - Olivier Cases
- Centre de Recherche des Cordeliers, Sorbonne Université, INSERM, Université de Paris, Paris, France
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5
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Fedosov SN, Nexo E, Heegaard CW. Vitamin B 12 and its binding proteins in milk from cow and buffalo in relation to bioavailability of B 12. J Dairy Sci 2019; 102:4891-4905. [PMID: 30928264 DOI: 10.3168/jds.2018-15016] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 02/07/2019] [Indexed: 11/19/2022]
Abstract
Milk is an important source of highly bioavailable vitamin B12 (cobalamin) in human nutrition. In most animal products, vitamin B12 is strongly bound to various specific protein carriers. The 2 vitamin B12-specific proteins, predominantly transcobalamin (TC) and haptocorrin (HC), were earlier found in milk from Holstein Friesian cows and in human or sow milk, respectively. As the type of vitamin B12 binders may influence bioavailability of the vitamin, we examined vitamin B12 carriers in pooled milk specimens derived from European and Indian cow and buffalo herds. The total endogenous vitamin B12 concentration was comparable in all milk pools (≈3 nM), but the vitamin carriers varied considerably: TC + caseins in Danish cows, TC + HC in Indian cows and buffaloes, and mainly HC in Italian buffaloes. Danish cow milk contained half as much TC as vitamin B12, and the surplus vitamin was all attached via a single coordination bond to abundantly available histidine residues of casein. The specific binding proteins in Indian cow milk (TC + HC) approximately matched the molar content of vitamin B12. Milk from the 2 buffalo breeds contained more specific binders than vitamin B12, and the surplus proteins included the unsaturated TC ≈ 3 nM (Indian stock), or both TC ≈ 4 nM and HC ≈ 23 nM (Italian stock). The abundant HC of the latter sample bound nearly all endogenous vitamin B12. We tested (in vitro) the transfer of vitamin B12 from milk proteins to human carriers, involved in the intestinal uptake. The bovine TC-vitamin B12 complex rapidly dissociated at pH 2 (time of half reaction, τ1/2 < 1 min, 37°C) and was susceptible to digestion with trypsin + chymotrypsin (pH 7.5). Transfer of vitamin B12 from the precipitated bovine casein (pH 2) to human carriers proceeded with τ1/2 ≈ 7 min (37°C) and τ1/2 ≈ 35 min (20°C). Liberation of vitamin B12 from buffalo HC was hampered because of its pH stability and slow proteolysis. Nutritional availability of vitamin B12 is expected to be high in cow milk (with TC-vitamin B12 and casein-vitamin B12 complexes) but potentially constrained in buffalo milk (with HC-vitamin B12). This especially concerns the Italian buffalo milk, where a high excess of HC was found. We speculate whether the isolated stock of Italian buffalo maintained the ancestral secretion of carriers (HC ≫ vitamin B12, TC ≈ 0), whereas intensive crossbreeding of cows and buffaloes from other regions caused a change to TC ≤ vitamin B12, with low or absent HC. The substitution of HC by less sturdy carriers is apparently more beneficial to human consumers as far as vitamin B12 bioavailability is concerned.
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Affiliation(s)
- Sergey N Fedosov
- Department of Molecular Biology and Genetics, Aarhus University, Science Park, Gustav Wieds Vej 10C 8000, Aarhus C, Denmark.
| | - Ebba Nexo
- Department of Clinical Biochemistry, Aarhus University Hospital, Palle Juul-Jensens Boulevard 99, 8200 Aarhus N, Denmark
| | - Christian W Heegaard
- Department of Molecular Biology and Genetics, Aarhus University, Science Park, Gustav Wieds Vej 10C 8000, Aarhus C, Denmark
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6
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Kozyraki R, Cases O. Cubilin, the Intrinsic Factor-Vitamin B12 Receptor in Development and Disease. Curr Med Chem 2018; 27:3123-3150. [PMID: 30295181 DOI: 10.2174/0929867325666181008143945] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2018] [Revised: 08/11/2018] [Accepted: 08/21/2018] [Indexed: 12/29/2022]
Abstract
Gp280/Intrinsic factor-vitamin B12 receptor/Cubilin (CUBN) is a large endocytic receptor serving multiple functions in vitamin B12 homeostasis, renal reabsorption of protein or toxic substances including albumin, vitamin D-binding protein or cadmium. Cubilin is a peripheral membrane protein consisting of 8 Epidermal Growth Factor (EGF)-like repeats and 27 CUB (defined as Complement C1r/C1s, Uegf, BMP1) domains. This structurally unique protein interacts with at least two molecular partners, Amnionless (AMN) and Lrp2/Megalin. AMN is involved in appropriate plasma membrane transport of Cubilin whereas Lrp2 is essential for efficient internalization of Cubilin and its ligands. Observations gleaned from animal models with Cubn deficiency or human diseases demonstrate the importance of this protein. In this review addressed to basic research and medical scientists, we summarize currently available data on Cubilin and its implication in renal and intestinal biology. We also discuss the role of Cubilin as a modulator of Fgf8 signaling during embryonic development and propose that the Cubilin-Fgf8 interaction may be relevant in human pathology, including in cancer progression, heart or neural tube defects. We finally provide experimental elements suggesting that some aspects of Cubilin physiology might be relevant in drug design.
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Affiliation(s)
- Renata Kozyraki
- INSERM UMRS 1138, Centre de Recherche des Cordeliers, Paris-Diderot University, Paris, France
| | - Olivier Cases
- INSERM UMRS 1138, Centre de Recherche des Cordeliers, Paris-Diderot University, Paris, France
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7
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Structure of the human transcobalamin beta domain in four distinct states. PLoS One 2017; 12:e0184932. [PMID: 28910388 PMCID: PMC5599065 DOI: 10.1371/journal.pone.0184932] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Accepted: 09/02/2017] [Indexed: 11/19/2022] Open
Abstract
Vitamin B12 (cyanocobalamin, CNCbl) is an essential cofactor-precursor for two biochemical reactions in humans. When ingested, cobalamins (Cbl) are transported via a multistep transport system into the bloodstream, where the soluble protein transcobalamin (TC) binds Cbl and the complex is taken up into the cells via receptor mediated endocytosis. Crystal structures of TC in complex with CNCbl have been solved previously. However, the initial steps of holo-TC assembly have remained elusive. Here, we present four crystal structures of the beta domain of human TC (TC-beta) in different substrate-bound states. These include the apo and CNCbl-bound states, providing insight into the early steps of holo-TC assembly. We found that in vitro assembly of TC-alpha and TC-beta to a complex was Cbl-dependent. We also determined the structure of TC-beta in complex with cobinamide (Cbi), an alternative substrate, shedding light on the specificity of TC. We finally determined the structure of TC-beta in complex with an inhibitory antivitamin B12 (anti-B12). We used this structure to model the binding of anti-B12 into full-length holo-TC and could rule out that the inhibitory function of anti-B12 was based on an inability to form a functional complex with TC.
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8
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Theoretical approximations and experimental extinction coefficients of biopharmaceuticals. Anal Bioanal Chem 2015; 408:1523-30. [DOI: 10.1007/s00216-015-9261-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Revised: 12/02/2015] [Accepted: 12/08/2015] [Indexed: 01/25/2023]
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9
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Analysis of therapeutic proteins and peptides using multiangle light scattering coupled to ultra high performance liquid chromatography. J Sep Sci 2015; 38:1537-43. [DOI: 10.1002/jssc.201400863] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Revised: 01/30/2015] [Accepted: 02/08/2015] [Indexed: 01/28/2023]
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10
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Abstract
Minute doses of a complex cofactor cobalamin (Cbl, vitamin B12) are essential for metabolism. The nutritional chain for humans includes: (1) production of Cbl by bacteria in the intestinal tract of herbivores; (2) accumulation of the absorbed Cbl in animal tissues; (3) consumption of food of animal origin. Most biological sources contain both Cbl and its analogues, i.e. Cbl-resembling compounds physiologically inactive in animal cells. Selective assimilation of the true vitamin requires an interplay between three transporting proteins - haptocorrin (HC), intrinsic factor (IF), transcobalamin (TC) - and several receptors. HC is present in many biological fluids, including gastric juice, where it assists in disposal of analogues. Gastric IF selectively binds dietary Cbl and enters the intestinal cells via receptor-mediated endocytosis. Absorbed Cbl is transmitted to TC and delivered to the tissues with blood flow. The complex transport system guarantees a very efficient uptake of the vitamin, but failure at any link causes Cbl-deficiency. Early detection of a negative B12 balance is highly desirable to prevent irreversible neurological damages, anaemia and death in aggravated cases. The review focuses on the molecular mechanisms of cobalamin transport with emphasis on interaction of corrinoids with the specific proteins and protein-receptor recognition. The last section briefly describes practical aspects of recent basic research concerning early detection of B12-related disorders, medical application of Cbl-conjugates, and purification of corrinoids from biological samples.
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Affiliation(s)
- Sergey N Fedosov
- Protein Chemistry Laboratory, Department of Molecular Biology, University of Aarhus, Aarhus, Denmark,
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11
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Tran MTQ, Furger E, Alberto R. Two-step activation prodrugs: transplatin mediated binding of chemotherapeutic agents to vitamin B12. Org Biomol Chem 2013; 11:3247-54. [PMID: 23584074 DOI: 10.1039/c3ob40093j] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Clinically approved organic chemotherapeutic drugs such as cytarabine, dacarbazine and anastrozole were attached to B12via a {CN-trans-Pt(NH3)2}-bridge to yield [{Co}-CN-{trans-Pt(NH3)2}-{drug}](2+). The active organic drugs are protected by the platinum complex and by B12, which represents at the same time the targeting vector. We refer to these bioconjugates as two-step activation prodrugs since two reactions are finally required to liberate the actual organic drugs. All three prodrugs are soluble and stable in water. The physiological stability and the therapeutic efficiency of [{Co}-CN-{trans-Pt(NH3)2}-{cytarabine}](2+) (2) were studied. Under physiological conditions, 2 is stable for 3 days. Its affinity to the cobalamin transport proteins (haptocorrin, intrinsic factor and transcobalamin) is not substantially affected despite the introduction of a bulky group in the β-axial position. The cleavage of the [trans-CN-Pt(NH3)2-{cytarabine}](+) complex was observed upon chemical reduction of Co(III)→ Co(II) with Zn(0). Cytarabine was subsequently released from the cleaved complex to exhibit its cytotoxicity. 2 displayed a reduced cytotoxicity (IC50 = 230 ± 62 nM) as compared to cytarabine (IC50 = 30 ± 5 nM). However, cytarabine released from 2 showed comparable cytotoxicity (IC50 = 30 ± 11 nM).
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Affiliation(s)
- Mai Thanh Quynh Tran
- Institute of Inorganic Chemistry, University of Zürich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
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12
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Fedosov SN, Ruetz M, Gruber K, Fedosova NU, Kräutler B. A Blue Corrinoid from Partial Degradation of Vitamin B12 in Aqueous Bicarbonate: Spectra, Structure, and Interaction with Proteins of B12 Transport. Biochemistry 2011; 50:8090-101. [DOI: 10.1021/bi200724s] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sergey N. Fedosov
- Department of Molecular Biology
and Genetics, Aarhus University, Science
Park, Gustav Wieds Vej 10, DK 8000 Aarhus C, Denmark
| | - Markus Ruetz
- Institute of Organic Chemistry
and Center of Molecular Biosciences, University of Innsbruck, Innrain 52A, Innsbruck A-6020, Austria
| | - Karl Gruber
- Institute of Molecular Biosciences, University of Graz, Humboldtstrasse 50/3, Graz A-8010,
Austria
| | - Natalya U. Fedosova
- Department of Biomedicine, Aarhus University, Ole Worms Alle 1185, DK 8000 Aarhus
C, Denmark
| | - Bernhard Kräutler
- Institute of Organic Chemistry
and Center of Molecular Biosciences, University of Innsbruck, Innrain 52A, Innsbruck A-6020, Austria
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13
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Andersen CBF, Madsen M, Storm T, Moestrup SK, Andersen GR. Structural basis for receptor recognition of vitamin-B12–intrinsic factor complexes. Nature 2010; 464:445-8. [DOI: 10.1038/nature08874] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2009] [Accepted: 02/02/2010] [Indexed: 11/09/2022]
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14
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Lee M, Grissom CB. Design, synthesis, and characterization of fluorescent cobalamin analogues with high quantum efficiencies. Org Lett 2009; 11:2499-502. [PMID: 19441855 DOI: 10.1021/ol900401z] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cobalamin tethered to fluorescein or Rhodamine 6G has been synthesized and characterized. The fluorophore is conjugated to the ribose-5'-OH of cobalamin through a rigid linker to prevent the fluorophore from folding back through space and interacting with the corrin ring of cobalamin. This increases the fluorescence quantum yield. This new family of cobalamin analogues may be suitable for use as tumor markers to tag cancer cells for surgical resection.
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Affiliation(s)
- Manfai Lee
- Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0850, USA
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15
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Sukumar N, Mathews FS, Gordon MM, Ealick SE, Alpers DH. Postcrystallization Analysis of the Irreproducibility of the Human Intrinsic Factor-Cobalamin Complex Crystals. CRYSTAL GROWTH & DESIGN 2009; 9:348-351. [PMID: 19884970 PMCID: PMC2631276 DOI: 10.1021/cg800509f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Approximately 15% (w/w) of human intrinsic factor (IF) is comprised of carbohydrate side chains, making crystallization problematic. In addition, IF is sensitive to proteolysis. To understand the role of these factors in crystallization, we carried out dynamic light scattering studies and assessed their correlation with crystallization. The packing of the IF-cobalamin complex and the known properties of the protein in solution were also analyzed to explore the irreproducibility of the IF-cobalamin complex crystals and the difficulty in obtaining apo-IF crystals suitable for crystallographic analysis. The results indicate that although glycosylation may in general be inhibitory for crystallization, time-dependent proteolysis appears to play a much more important role in the process of crystallization of IF. Thus, the presence of cobalamin and of domain fragments that can form incomplete dimers lacking one of two β-domains appears to promote the crystallization of IF.
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16
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Pérez-Marín MC, Padmanabhan S, Polanco MC, Murillo FJ, Elías-Arnanz M. Vitamin B12 partners the CarH repressor to downregulate a photoinducible promoter in Myxococcus xanthus. Mol Microbiol 2008; 67:804-19. [PMID: 18315685 DOI: 10.1111/j.1365-2958.2007.06086.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A light-inducible promoter, P(B), drives expression of the carB operon in Myxococcus xanthus. Repressed by CarA in the dark, P(B) is activated when CarS, produced in the light, sequesters CarA to prevent operator-CarA binding. The MerR-type, N-terminal domain of CarA, which mediates interactions with both operator and CarS, is linked to a C-terminal oligomerization module with a predicted cobalamin-binding motif. Here, we show that although CarA does bind vitamin B12, mutating the motif involved has no effect on its ability to repress P(B). Intriguingly, P(B) could be repressed in the dark even with no CarA, so long as B12 and an intact CarA operator were present. We have discovered that this effect of B12 depends on the gene immediately downstream of carA. Its product, CarH, also consists of a MerR-type, N-terminal domain that specifically recognizes the CarA operator and CarS, linked to a predicted B12-binding C-terminal oligomerization module. The B12-mediated repression of P(B) in the dark is relieved by deleting carH, by mutating the DNA- or B12-binding residues of CarH, or by illumination. Our findings unveil parallel regulatory circuits that control a light-inducible promoter using a transcriptional factor repertoire that includes a paralogous gene pair and vitamin B12.
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Affiliation(s)
- Mari Cruz Pérez-Marín
- Departamento de Genética y Microbiología, Area de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia 30100, Spain
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17
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Crystal structure of human intrinsic factor: cobalamin complex at 2.6-A resolution. Proc Natl Acad Sci U S A 2007; 104:17311-6. [PMID: 17954916 DOI: 10.1073/pnas.0703228104] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The structure of intrinsic factor (IF) in complex with cobalamin (Cbl) was determined at 2.6-A resolution. The overall fold of the molecule is that of an alpha(6)/alpha(6) barrel. It is a two-domain protein, and the Cbl is bound at the interface of the domains in a base-on conformation. Surprisingly, two full-length molecules, each comprising an alpha- and a beta-domain and one Cbl, and two truncated molecules with only an alpha- domain are present in the same asymmetric unit. The environment around Cbl is dominated by uncharged residues, and the sixth coordinate position of Co(2+) is empty. A detailed comparison between the IF-B12 complex and another Cbl transport protein complex, trans-Cbl-B12, has been made. The pH effect on the binding of Cbl analogues in transport proteins is analyzed. A possible basis for the lack of interchangeability of human and rat IF receptors is presented.
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18
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Wuerges J, Geremia S, Randaccio L. Structural study on ligand specificity of human vitamin B12 transporters. Biochem J 2007; 403:431-40. [PMID: 17274763 PMCID: PMC1876373 DOI: 10.1042/bj20061394] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Studies comparing the binding of genuine cobalamin (vitamin B12) to that of its natural or synthetic analogues have long established increasing ligand specificity in the order haptocorrin, transcobalamin and intrinsic factor, the high-affinity binding proteins involved in cobalamin transport in mammals. In the present study, ligand specificity was investigated from a structural point of view, for which comparative models of intrinsic factor and haptocorrin are produced based on the crystal structure of the homologous transcobalamin and validated by results of published binding assays. Many interactions between cobalamin and its binding site in the interface of the two domains are conserved among the transporters. A structural comparison suggests that the determinant of specificity regarding cobalamin ligands with modified nucleotide moiety resides in the beta-hairpin motif beta3-turn-beta4 of the smaller C-terminal domain. In haptocorrin, it provides hydrophobic contacts to the benzimidazole moiety through the apolar regions of Arg357, Trp359 and Tyr362. Together, these large side chains may compensate for the missing nucleotide upon cobinamide binding. Intrinsic factor possesses only the tryptophan residue and transcobalamin only the tyrosine residue, consistent with their low affinity for cobinamide. Relative affinity constants for other analogues are rationalized similarly by analysis of steric and electrostatic interactions with the three transporters. The structures also indicate that the C-terminal domain is the first site of cobalamin-binding since part of the beta-hairpin motif is trapped between the nucleotide moiety and the N-terminal domain in the final holo-proteins.
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Affiliation(s)
- Jochen Wuerges
- Centre of Excellence in Biocrystallography, Department of Chemical Sciences, University of Trieste, Via L. Giorgieri 1, 34127 Trieste, Italy
| | - Silvano Geremia
- Centre of Excellence in Biocrystallography, Department of Chemical Sciences, University of Trieste, Via L. Giorgieri 1, 34127 Trieste, Italy
- To whom correspondence should be addressed (email )
| | - Lucio Randaccio
- Centre of Excellence in Biocrystallography, Department of Chemical Sciences, University of Trieste, Via L. Giorgieri 1, 34127 Trieste, Italy
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Fedosov SN, Grissom CB, Fedosova NU, Moestrup SK, Nexø E, Petersen TE. Application of a fluorescent cobalamin analogue for analysis of the binding kinetics. A study employing recombinant human transcobalamin and intrinsic factor. FEBS J 2006; 273:4742-53. [PMID: 16984395 DOI: 10.1111/j.1742-4658.2006.05478.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Fluorescent probe rhodamine was appended to 5' OH-ribose of cobalamin (Cbl). The prepared conjugate, CBC, bound to the transporting proteins, intrinsic factor (IF) and transcobalamin (TC), responsible for the uptake of Cbl in an organism. Pronounced increase in fluorescence upon CBC attachment facilitated detailed kinetic analysis of Cbl binding. We found that TC had the same affinity for CBC and Cbl (K(d) = 5 x 10(-15) m), whereas interaction of CBC with the highly specific protein IF was more complex. For instance, CBC behaved normally in the partial reactions CBC + IF(30) and CBC + IF(20) when binding to the isolated IF fragments (domains). The ligand could also assemble them into a stable complex IF(30)-CBC-IF(20) with higher fluorescent signal. However, dissociation of IF(30)-CBC-IF(20) and IF-CBC was accelerated by factors of 3 and 20, respectively, when compared to the corresponding Cbl complexes. We suggest that the correct domain-domain interactions are the most important factor during recognition and fixation of the ligands by IF. Dissociation of IF-CBC was biphasic, and existence of multiple protein-analogue complexes with normal and partially corrupted structure may explain this behaviour. The most stable component had K(d) = 1.5 x 10(-13) m, which guarantees the binding of CBC to IF under physiological conditions. The specific intestinal receptor cubilin bound both IF-CBC and IF-Cbl with equal affinity. In conclusion, the fluorescent analogue CBC can be used as a reporting agent in the kinetic studies, moreover, it seems to be applicable for imaging purposes in vivo.
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Affiliation(s)
- Sergey N Fedosov
- Protein Chemistry Laboratory, Department of Molecular Biology, University of Aarhus, Denmark.
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Moestrup SK. New insights into carrier binding and epithelial uptake of the erythropoietic nutrients cobalamin and folate. Curr Opin Hematol 2006; 13:119-23. [PMID: 16567952 DOI: 10.1097/01.moh.0000219654.65538.5b] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
PURPOSE OF REVIEW In addition to malnutrition several genetic and acquired conditions may affect the homeostasis of cobalamin (vitamin B12) and folate, leading to megaloblastic anemia and other diseases. The present review describes new insight into protein handling of cobalamin and folate. RECENT FINDINGS The recent solution of the three-dimensional structure of the cobalamin binder transcobalamin shows two separate domains enclosing the vitamin. This structure apparently also applies for the other homologous cobalamin binders, intrinsic factor and haptocorrin. Genetic studies of inherited cobalamin malabsorption and biochemical studies have now revealed that the functional receptor for uptake of intrinsic factor-vitamin cobalamin complexes also is a complex itself consisting of two different gene products, cubilin and amnionless. A role in folate uptake of megalin, an endocytic receptor for epithelial uptake of various proteins including transcobalamin, is now also indicated by the observation that megalin can mediate uptake of soluble folate receptor. SUMMARY New data show the structure of cobalamin carriers and reveal novel proteins involved in the epithelial uptake of cobalamin and folate. Genetic abnormalities in three different genes encoding proteins in the epithelial uptake of cobalamin are now known to cause malabsorption of cobalamin and megaloblastic anemia.
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Affiliation(s)
- Søren K Moestrup
- Department of Medical Biochemistry, University of Aarhus, Denmark.
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Wuerges J, Garau G, Geremia S, Fedosov SN, Petersen TE, Randaccio L. Structural basis for mammalian vitamin B12 transport by transcobalamin. Proc Natl Acad Sci U S A 2006; 103:4386-91. [PMID: 16537422 PMCID: PMC1450181 DOI: 10.1073/pnas.0509099103] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2005] [Indexed: 11/18/2022] Open
Abstract
Cobalamin (Cbl, vitamin B(12)) serves for two essential cofactors in mammals. The pathway for its intestinal absorption, plasma transport, and cellular uptake uses cell surface receptors and three Cbl-transporting proteins, haptocorrin, intrinsic factor, and transcobalamin (TC). We present the structure determination of a member of the mammalian Cbl-transporter family. The crystal structures of recombinant human and bovine holo-TCs reveal a two-domain architecture, with an N-terminal alpha(6)-alpha(6) barrel and a smaller C-terminal domain. One Cbl molecule in base-on conformation is buried inside the domain interface. Structural data combined with previous binding assays indicate a domain motion in the first step of Cbl binding. In a second step, the weakly coordinated ligand H(2)O at the upper axial side of added H(2)O-Cbl is displaced by a histidine residue of the alpha(6)-alpha(6) barrel. Analysis of amino acid conservation on TC's surface in orthologous proteins suggests the location of the TC-receptor-recognition site in an extended region on the alpha(6)-alpha(6) barrel. The TC structure allows for the mapping of sites of amino acid variation due to polymorphisms of the human TC gene. Structural information is used to predict the overall fold of haptocorrin and intrinsic factor and permits a rational approach to the design of new Cbl-based bioconjugates for diagnostic or therapeutic drug delivery.
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Affiliation(s)
- Jochen Wuerges
- *Centre of Excellence in Biocrystallography, Department of Chemical Sciences, University of Trieste, Via L. Giorgieri 1, I-34127 Trieste, Italy; and
| | - Gianpiero Garau
- *Centre of Excellence in Biocrystallography, Department of Chemical Sciences, University of Trieste, Via L. Giorgieri 1, I-34127 Trieste, Italy; and
| | - Silvano Geremia
- *Centre of Excellence in Biocrystallography, Department of Chemical Sciences, University of Trieste, Via L. Giorgieri 1, I-34127 Trieste, Italy; and
| | - Sergey N. Fedosov
- Protein Chemistry Laboratory, Department of Molecular Biology, University of Aarhus, Science Park, Gustav Wieds Vey 10, 8000 Aarhus C, Denmark
| | - Torben E. Petersen
- Protein Chemistry Laboratory, Department of Molecular Biology, University of Aarhus, Science Park, Gustav Wieds Vey 10, 8000 Aarhus C, Denmark
| | - Lucio Randaccio
- *Centre of Excellence in Biocrystallography, Department of Chemical Sciences, University of Trieste, Via L. Giorgieri 1, I-34127 Trieste, Italy; and
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Orning L, Rian A, Campbell A, Brady J, Fedosov SN, Bramlage B, Thompson K, Quadros EV. Characterization of a monoclonal antibody with specificity for holo-transcobalamin. Nutr Metab (Lond) 2006; 3:3. [PMID: 16393340 PMCID: PMC1351188 DOI: 10.1186/1743-7075-3-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2005] [Accepted: 01/04/2006] [Indexed: 11/13/2022] Open
Abstract
Background Holotranscobalamin, cobalamin-saturated transcobalamin, is the minor fraction of circulating cobalamin (vitamin B12), which is available for cellular uptake and hence is physiologically relevant. Currently, no method allows simple, direct quantification of holotranscobalamin. We now report on the identification and characterization of a monoclonal antibody with a unique specificity for holotranscobalamin. Methods The specificity and affinity of the monoclonal antibodies were determined using surface plasmon resonance and recombinant transcobalamin as well as by immobilizing the antibodies on magnetic microspheres and using native transcobalamin in serum. The epitope of the holotranscobalamin specific antibody was identified using phage display and comparison to a de novo generated three-dimensional model of transcobalamin using the program Rosetta. A direct assay for holotrnscobalamin in the ELISA format was developed using the specific antibody and compared to the commercial assay HoloTC RIA. Results An antibody exhibiting >100-fold specificity for holotranscobalamin over apotranscobalamin was identified. The affinity but not the specificity varied inversely with ionic strength and pH, indicating importance of electrostatic interactions. The epitope was discontinuous and epitope mapping of the antibody by phage display identified two similar motifs with no direct sequence similarity to transcobalamin. A comparison of the motifs with a de novo generated three-dimensional model of transcobalamin identified two structures in the N-terminal part of transcobalamin that resembled the motif. Using this antibody an ELISA based prototype assay was developed and compared to the only available commercial assay for measuring holotranscobalamin, HoloTC RIA. Conclusion The identified antibody possesses a unique specificity for holotranscobalamin and can be used to develop a direct assay for the quantification of holotranscobalamin.
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Affiliation(s)
- Lars Orning
- Axis-Shield AS, POB 206 Økern, N-0510 Oslo, Norway
| | - Anne Rian
- Axis-Shield AS, POB 206 Økern, N-0510 Oslo, Norway
| | | | - Jeff Brady
- Axis-Shield AS, POB 206 Økern, N-0510 Oslo, Norway
| | - Sergey N Fedosov
- Protein Chemistry Laboratory, Department of Molecular and Structural Biology, University of Aarhus, Science Park, Gustav Wieds Vej 10, 8000 Aarhus
| | - Birgit Bramlage
- Axis-Shield AS, POB 206 Økern, N-0510 Oslo, Norway
- Alnylam Europe AG, Fritz-Hornschuch-Str. 9, 95326 Kulmbach, Germany
| | - Keith Thompson
- Institute of Immunology, Rikshospitalet University Hospital, University of Oslo, N-0027 Oslo, Norway
| | - Edward V Quadros
- Division of Hematology/Oncology, State University of New York, Health Science Center, Brooklyn, NY 11203, USA
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Fedosov SN, Orning L, Løvli T, Quadros EV, Thompson K, Berglund L, Petersen TE. Mapping the functional domains of human transcobalamin using monoclonal antibodies. FEBS J 2005; 272:3887-98. [PMID: 16045759 DOI: 10.1111/j.1742-4658.2005.04805.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Recombinant human transcobalamin (TC) was probed with 17 monoclonal antibodies (mAbs), using surface plasmon resonance measurements. These experiments identified five distinct epitope clusters on the surface of holo-TC. Western blot analysis of the CNBr cleavage fragments of TC allowed us to distribute the epitopes between two regions, which spanned either the second quarter of the TC sequence GQLA...TAAM(103-198) or the C-terminal peptide LEPA...LVSW(316-427). Proteolytic fragments of TC and the synthetic peptides were used to further specify the epitope map and define the functional domains of TC. Only one antibody showed some interference with cobalamin (Cbl) binding to TC, and the corresponding epitope was situated at the C-terminal stretch TQAS...QLLR(372-399). We explored the receptor-blocking effect of several mAbs and heparin to identify TC domains essential for the interaction between holo-TC and the receptor. The receptor-related epitopes were located within the TC sequence GQLA...HHSV(103-159). The putative heparin-binding site corresponded to a positively charged segment KRSN...RTVR(207-227), which also seemed to be necessary for receptor binding. We conclude that conformational changes in TC upon Cbl binding are accompanied by the convergence of multiple domains, and only the assembled conformation of the protein (i.e. holo-TC) has high affinity for the receptor.
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Affiliation(s)
- Sergey N Fedosov
- Protein Chemistry Laboratory, Department of Molecular Biology, University of Aarhus,Denmark.
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Abstract
The year 2004 represents a milestone for the biosensor research community: in this year, over 1000 articles were published describing experiments performed using commercially available systems. The 1038 papers we found represent an approximately 10% increase over the past year and demonstrate that the implementation of biosensors continues to expand at a healthy pace. We evaluated the data presented in each paper and compiled a 'top 10' list. These 10 articles, which we recommend every biosensor user reads, describe well-performed kinetic, equilibrium and qualitative/screening studies, provide comparisons between binding parameters obtained from different biosensor users, as well as from biosensor- and solution-based interaction analyses, and summarize the cutting-edge applications of the technology. We also re-iterate some of the experimental pitfalls that lead to sub-optimal data and over-interpreted results. We are hopeful that the biosensor community, by applying the hints we outline, will obtain data on a par with that presented in the 10 spotlighted articles. This will ensure that the scientific community at large can be confident in the data we report from optical biosensors.
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Affiliation(s)
- Rebecca L Rich
- Center for Biomolecular Interaction Analysis, University of Utah, Salt Lake City, UT 84132, USA
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