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Sutton BJ, Davies AM. Structure and dynamics of IgE-receptor interactions: FcεRI and CD23/FcεRII. Immunol Rev 2015; 268:222-35. [DOI: 10.1111/imr.12340] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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Davies AM, Tata R, Trentham DR, Sutton BJ, Brown PR. Characterisation of a phosphinothricin N-acetyltransferase from Pseudomonas syringae. Acta Crystallogr A Found Adv 2015. [DOI: 10.1107/s2053273315096576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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Mitropoulou AN, Davies AM, Dodev TS, James LK, Beavil RL, Gould HJ, McDonnell JM, Beavil AJ, Sutton BJ. The crystal structure of a common allergen in complex with its specific patient-derived antibody. Acta Crystallogr A Found Adv 2015. [DOI: 10.1107/s2053273315096059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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Hussein D, Starr A, Heikal L, McNeill E, Channon KM, Brown PR, Sutton BJ, McDonnell JM, Nandi M. Validating the GTP-cyclohydrolase 1-feedback regulatory complex as a therapeutic target using biophysical and in vivo approaches. Br J Pharmacol 2015; 172:4146-57. [PMID: 26014146 PMCID: PMC4543619 DOI: 10.1111/bph.13202] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2014] [Revised: 05/12/2015] [Accepted: 05/13/2015] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND AND PURPOSE 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4 ) is an essential cofactor for nitric oxide biosynthesis. Substantial clinical evidence indicates that intravenous BH4 restores vascular function in patients. Unfortunately, oral BH4 has limited efficacy. Therefore, orally bioavailable pharmacological activators of endogenous BH4 biosynthesis hold significant therapeutic potential. GTP-cyclohydrolase 1 (GCH1), the rate limiting enzyme in BH4 synthesis, forms a protein complex with GCH1 feedback regulatory protein (GFRP). This complex is subject to allosteric feed-forward activation by L-phenylalanine (L-phe). We investigated the effects of L-phe on the biophysical interactions of GCH1 and GFRP and its potential to alter BH4 levels in vivo. EXPERIMENTAL APPROACH Detailed characterization of GCH1-GFRP protein-protein interactions were performed using surface plasmon resonance (SPR) with or without L-phe. Effects on systemic and vascular BH4 biosynthesis in vivo were investigated following L-phe treatment (100 mg·kg(-1) , p.o.). KEY RESULTS GCH1 and GFRP proteins interacted in the absence of known ligands or substrate but the presence of L-phe doubled maximal binding and enhanced binding affinity eightfold. Furthermore, the complex displayed very slow association and dissociation rates. In vivo, L-phe challenge induced a sustained elevation of aortic BH4 , an effect absent in GCH1(fl/fl)-Tie2Cre mice. CONCLUSIONS AND IMPLICATIONS Biophysical data indicate that GCH1 and GFRP are constitutively bound. In vivo, data demonstrated that L-phe elevated vascular BH4 in an endothelial GCH1 dependent manner. Pharmacological agents which mimic the allosteric effects of L-phe on the GCH1-GFRP complex have the potential to elevate endothelial BH4 biosynthesis for numerous cardiovascular disorders.
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Baloch AR, Baloch AW, Sutton BJ, Zhang X. Antibody mimetics: promising complementary agents to animal-sourced antibodies. Crit Rev Biotechnol 2014; 36:268-75. [PMID: 25264572 DOI: 10.3109/07388551.2014.958431] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Despite their wide use as therapeutic, diagnostic and detection agents, the limitations of polyclonal and monoclonal antibodies have inspired scientists to design the next generation biomedical agents, so-called antibody mimetics that offer many advantages over conventional antibodies. Antibody mimetics can be constructed by protein-directed evolution or fusion of complementarity-determining regions through intervening framework regions. Substantial progress in exploiting human, butterfly (Pieris brassicae) and bacterial systems to design and select mimetics using display technologies has been made in the past 10 years, and one of these mimetics [Kalbitor® (Dyax)] has made its way to market. Many challenges lie ahead to develop mimetics for various biomedical applications, especially those for which conventional antibodies are ineffective, and this review describes the current characteristics, construction and applications of antibody mimetics compared to animal-sourced antibodies. The possible limitations of mimetics and future perspectives are also discussed.
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Levin M, Davies AM, Liljekvist M, Carlsson F, Gould HJ, Sutton BJ, Ohlin M. Human IgE against the major allergen Bet v 1--defining an epitope with limited cross-reactivity between different PR-10 family proteins. Clin Exp Allergy 2014; 44:288-99. [PMID: 24447087 PMCID: PMC4215112 DOI: 10.1111/cea.12230] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Revised: 09/24/2013] [Accepted: 10/25/2013] [Indexed: 02/05/2023]
Abstract
Background The interaction between IgE and allergen is a key event at the initiation of an allergic response, and its characteristics have substantial effects on the clinical manifestation. Despite this, the molecular details of the interaction between human IgE and the major birch allergen Bet v 1, one of the most potent tree allergens, still remain poorly investigated. Objective To isolate Bet v 1-specific human monoclonal IgE and characterize their interaction with the allergen. Methods Recombinant human IgE were isolated from a combinatorial antibody fragment library and their interaction with Bet v 1 assessed using various immunological assays. The structure of one such IgE in the single-chain fragment variable format was determined using X-ray crystallography. Results We present four novel Bet v 1-specific IgE, for one of which we solve the structure, all with their genetic origin in the IGHV5 germline gene, and demonstrate that they target two non-overlapping epitopes on the surface of Bet v 1, thereby fulfilling the basic criteria for FcεRI cross-linkage. We further define these epitopes and for one epitope pinpoint single amino acid residues important for the interaction with human IgE. This provides a potential explanation, at the molecular level, for the differences in recognition of isoforms of Bet v 1 and other allergens in the PR-10 protein family displayed by IgE targeting this epitope. Finally, we present the first high-resolution structure of a human allergen-specific IgE fragment in the single-chain fragment variable (scFv) format. Conclusions and Clinical Relevance We here display the usefulness of allergen-specific human monoclonal IgE as a tool in studies of the crucial molecular interaction taking place at the initiation of an allergic response. Such studies may aid us in development of better diagnostic tools and guide us in the development of new therapeutic compounds.
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Davies AM, Jefferis R, Sutton BJ. Crystal structure of deglycosylated human IgG4-Fc. Mol Immunol 2014; 62:46-53. [PMID: 24956411 PMCID: PMC4166458 DOI: 10.1016/j.molimm.2014.05.015] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2014] [Accepted: 05/29/2014] [Indexed: 12/24/2022]
Abstract
The first crystal structure of deglycosylated human IgG4-Fc is reported at 2.7 Å resolution. The asymmetric unit comprises a novel interlocked arrangement of two IgG4-Fc molecules. The CH2 domains are oriented in an “open” arrangement. The structure of the CH2 domain DE loop is altered in the absence of carbohydrate. Crystal packing reveals a hexameric Fc arrangement.
The Fc region of IgG antibodies, important for effector functions such as antibody-dependent cell-mediated cytotoxicity, antibody-dependent cellular phagocytosis and complement activation, contains an oligosaccharide moiety covalently attached to each CH2 domain. The oligosaccharide not only orients the CH2 domains but plays an important role in influencing IgG effector function, and engineering the IgG-Fc oligosaccharide moiety is an important aspect in the design of therapeutic monoclonal IgG antibodies. Recently we reported the crystal structure of glycosylated IgG4-Fc, revealing structural features that could explain the anti-inflammatory biological properties of IgG4 compared with IgG1. We now report the crystal structure of enzymatically deglycosylated IgG4-Fc, derived from human serum, at 2.7 Å resolution. Intermolecular CH2-CH2 domain interactions partially bury the CH2 domain surface that would otherwise be exposed by the absence of oligosaccharide, and two Fc molecules are interlocked in a symmetric, open conformation. The conformation of the CH2 domain DE loop, to which oligosaccharide is attached, is altered in the absence of carbohydrate. Furthermore, the CH2 domain FG loop, important for Fcγ receptor and C1q binding, adopts two different conformations. One loop conformation is unique to IgG4 and would disrupt binding, consistent with IgG4's anti-inflammatory properties. The second is similar to the conserved conformation found in IgG1, suggesting that in contrast to IgG1, the IgG4 CH2 FG loop is dynamic. Finally, crystal packing reveals a hexameric arrangement of IgG4-Fc molecules, providing further clues about the interaction between C1q and IgG.
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Drinkwater N, Cossins B, Keeble AH, Wright M, Cain K, Hailu H, Oxbrow A, Delgado J, Shuttleworth LK, Kao MWP, McDonnell JM, Beavil AJ, Henry AJ, Sutton BJ. Human immunoglobulin E flexes between acutely bent and extended conformations. Nat Struct Mol Biol 2014; 21:397-404. [PMID: 24632569 PMCID: PMC3977038 DOI: 10.1038/nsmb.2795] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Accepted: 02/13/2014] [Indexed: 11/17/2022]
Abstract
Crystallographic and solution studies have shown that IgE molecules are acutely bent in their Fc region. Crystal structures reveal the Cɛ2 domain pair folded back onto the Cɛ3-Cɛ4 domains, but is the molecule exclusively bent or can the Cɛ2 domains adopt extended conformations and even 'flip' from one side of the molecule to the other? We report the crystal structure of IgE-Fc captured in a fully extended, symmetrical conformation and show by molecular dynamics, calorimetry, stopped-flow kinetic, surface plasmon resonance (SPR) and Förster resonance energy transfer (FRET) analyses that the antibody can indeed adopt such extended conformations in solution. This diversity of conformational states available to IgE-Fc offers a new perspective on IgE function in allergen recognition, as part of the B-cell receptor and as a therapeutic target in allergic disease.
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Dhaliwal B, Pang MOY, Yuan D, Beavil AJ, Sutton BJ. A range of Cℇ3-Cℇ4 interdomain angles in IgE Fc accommodate binding to its receptor CD23. Acta Crystallogr F Struct Biol Commun 2014; 70:305-9. [PMID: 24598915 PMCID: PMC3944690 DOI: 10.1107/s2053230x14003355] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Accepted: 02/14/2014] [Indexed: 05/20/2024] Open
Abstract
The antibody IgE plays a central role in allergic disease, functioning principally through two cell-surface receptors: FcℇRI and CD23. FcℇRI on mast cells and basophils mediates the immediate hypersensitivity response, whilst the interaction of IgE with CD23 on B cells regulates IgE production. Crystal structures of the lectin-like `head' domain of CD23 alone and bound to a subfragment of IgE consisting of the dimer of Cℇ3 and Cℇ4 domains (Fcℇ3-4) have recently been determined, revealing flexibility in the IgE-binding site of CD23. Here, a new crystal form of the CD23-Fcℇ3-4 complex with different molecular-packing constraints is reported, which together with the earlier results demonstrates that conformational variability at the interface extends additionally to the IgE Fc and the quaternary structure of its domains.
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Godlewska M, Góra M, Buckle AM, Porebski BT, Kemp EH, Sutton BJ, Czarnocka B, Banga JP. A redundant role of human thyroid peroxidase propeptide for cellular, enzymatic, and immunological activity. Thyroid 2014; 24:371-82. [PMID: 23668778 PMCID: PMC3926150 DOI: 10.1089/thy.2013.0127] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
BACKGROUND Thyroid peroxidase (TPO) is a dimeric membrane-bound enzyme of thyroid follicular cells, responsible for thyroid hormone biosynthesis. TPO is also a common target antigen in autoimmune thyroid disease (AITD). With two active sites, TPO is an unusual enzyme, and thus there is much interest in understanding its structure and role in AITD. Homology modeling has shown TPO to be composed of different structural modules, as well as a propeptide sequence. During the course of studies to obtain homogeneous preparations of recombinant TPO for structural studies, we investigated the role of the large propeptide sequence in TPO. METHODS An engineered recombinant human TPO preparation expressed in Chinese hamster ovary (CHO) cells lacking the propeptide (TPOΔpro; amino acid residues 21-108) was characterized and its properties compared to wild-type TPO. Plasma membrane localization was determined by cell surface protein biotinylation, and biochemical studies were performed to evaluate enzymatic activity and the effect of deglycosylation. Immunological investigations using autoantibodies from AITD patients and other epitope-specific antibodies that recognize conformational determinants on TPO were evaluated for binding to TPOΔpro by flow cytometry, immunocytochemistry, and capture enzyme-linked immunosorbent assay. Molecular modeling and dynamics simulation of TPOΔpro comprising a dimer of myeloperoxidase-like domains was performed in order to investigate the impact of propeptide removal and the role of glycosylation. RESULTS The TPOΔpro was expressed on the cell surface at comparable levels to wild-type TPO. The TPOΔpro was enzymatically active and recognized by patients' autoantibodies and a panel of epitope-specific antibodies, confirming structural integrity of the two major conformational determinants recognized by autoantibodies. Faithful intracellular trafficking and N-glycosylation of TPOΔpro was also maintained. Molecular modeling and dynamics simulations were consistent with these observations. CONCLUSIONS Our results point to a redundant role for the propeptide sequence in TPO. The successful expression of TPOΔpro in a membrane-anchored, enzymatically active form that is insensitive to intramolecular proteolysis, and importantly is recognized by patients' autoantibodies, is a key advance for purification of substantial quantities of homogeneous preparation of TPO for crystallization, structural, and immunological studies.
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Rispens T, Davies AM, Ooijevaar-de Heer P, Absalah S, Bende O, Sutton BJ, Vidarsson G, Aalberse RC. Dynamics of inter-heavy chain interactions in human immunoglobulin G (IgG) subclasses studied by kinetic Fab arm exchange. J Biol Chem 2014; 289:6098-109. [PMID: 24425871 PMCID: PMC3937676 DOI: 10.1074/jbc.m113.541813] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Interdomain interactions between the CH3 domains of antibody heavy chains are the first step in antibody assembly and are of prime importance for maintaining the native structure of IgG. For human IgG4 it was shown that CH3-CH3 interactions are weak, resulting in the potential for half-molecule exchange (“Fab arm exchange”). Here we systematically investigated non-covalent interchain interactions for CH3 domains in the other human subclasses, including polymorphisms (allotypes), using real-time monitoring of Fab arm exchange with a FRET-based kinetic assay. We identified structural variation between human IgG subclasses and allotypes at three amino acid positions (Lys/Asn-392, Val/Met-397, Lys/Arg-409) to alter the strength of inter-domain interactions by >6 orders of magnitude. Each substitution affected the interactions independent from the other substitutions in terms of affinity, but the enthalpic and entropic contributions were non-additive, suggesting a complex interplay. Allotypic variation in IgG3 resulted in widely different CH3 interaction strengths that were even weaker for IgG3 than for IgG4 in the case of allotype G3m(c3c5*/6,24*), whereas G3m(s*/15*) was equally stable to IgG1. These interactions are sufficiently strong to maintain the structural integrity of IgG1 during its normal life span; for IgG2 and IgG3 the inter-heavy chain disulfide bonds are essential to prevent half-molecule dissociation, whereas the labile hinge disulfide bonds favor half-molecule exchange in vivo for IgG4.
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Tian Z, Sutton BJ, Zhang X. Distribution of rat neonatal Fc receptor in the principal organs of neonatal and pubertal rats. J Recept Signal Transduct Res 2013; 34:137-42. [PMID: 24303938 DOI: 10.3109/10799893.2013.865745] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The neonatal Fc receptor (FcRn) mediates the transfer of IgG and albumin, also protects them from catabolism. This study characterized the expression of FcRn in different organs of neonatal and pubertal rats by reverse transcription-PCR (RT-PCR) and immunohistochemistry, demonstrates that FcRn is expressed in liver, kidney, intestine, heart, lung, spleen, skin and skeletal muscles at varying levels post-gestation from d 1 to d 63. This finding is contrary to previous studies claiming that FcRn is undetectable in most tissues after weaning. Lungs were the predominant organs for FcRn expression, whereas skin, liver and intestine are considerably less expressed organs. The expression of FcRn fluctuated in all the organs tested, and with a higher frequency before weaning compared to puberty. These findings may provide clues for the better understanding of FcRn function, and are important for determining the dosage levels for IgG and the constant region fragment (Fc)-containing therapeutic proteins whose half-life is regulated by FcRn.
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Davies AM, Rispens T, Ooijevaar-de Heer P, Gould HJ, Jefferis R, Aalberse RC, Sutton BJ. Structural determinants of unique properties of human IgG4-Fc. J Mol Biol 2013; 426:630-44. [PMID: 24211234 PMCID: PMC3905167 DOI: 10.1016/j.jmb.2013.10.039] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Revised: 10/19/2013] [Accepted: 10/29/2013] [Indexed: 12/24/2022]
Abstract
Human IgG4, normally the least abundant of the four subclasses of IgG in serum, displays a number of unique biological properties. It can undergo heavy-chain exchange, also known as Fab-arm exchange, leading to the formation of monovalent but bispecific antibodies, and it interacts poorly with FcγRII and FcγRIII, and complement. These properties render IgG4 relatively “non-inflammatory” and have made it a suitable format for therapeutic monoclonal antibody production. However, IgG4 is also known to undergo Fc-mediated aggregation and has been implicated in auto-immune disease pathology. We report here the high-resolution crystal structures, at 1.9 and 2.35 Å, respectively, of human recombinant and serum-derived IgG4-Fc. These structures reveal conformational variability at the CH3–CH3 interface that may promote Fab-arm exchange, and a unique conformation for the FG loop in the CH2 domain that would explain the poor FcγRII, FcγRIII and C1q binding properties of IgG4 compared with IgG1 and -3. In contrast to other IgG subclasses, this unique conformation folds the FG loop away from the CH2 domain, precluding any interaction with the lower hinge region, which may further facilitate Fab-arm exchange by destabilisation of the hinge. The crystals of IgG4-Fc also display Fc–Fc packing contacts with very extensive interaction surfaces, involving both a consensus binding site in IgG-Fc at the CH2–CH3 interface and known hydrophobic aggregation motifs. These Fc–Fc interactions are compatible with intact IgG4 molecules and may provide a model for the formation of aggregates of IgG4 that can cause disease pathology in the absence of antigen. The first high-resolution crystal structures of IgG4-Fc have been solved. Arg409 adopts two conformations, each with a different effect on the CH3–CH3 interface. Crystal packing analysis reveals a novel Fc–Fc interface. The CH2 domain FG loop adopts a unique conformation, affecting FcγR and C1q binding. The IgG4-Fc crystal structures explain unique biological properties of IgG4.
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Davies AM, Rispens T, Heer POD, Gould HJ, Jefferis R, Aalberse RC, Sutton BJ. Unique structural features of human IgG4 Fc. Acta Crystallogr A 2013. [DOI: 10.1107/s0108767313097006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Drinkwater N, Cossins B, Keeble AH, Wright M, McDonnell JM, Beavil AJ, Henry AJ, Sutton BJ. Human IgE flips between two acutely bent structures viaan ensemble of extended conformations. Acta Crystallogr A 2013. [DOI: 10.1107/s010876731309702x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Dhaliwal B, Pang MO, Yuan D, Yahya N, Fabiane SM, McDonnell JM, Gould HJ, Beavil AJ, Sutton BJ. Conformational plasticity at the IgE-binding site of the B-cell receptor CD23. Mol Immunol 2013; 56:693-7. [PMID: 23933509 PMCID: PMC3807792 DOI: 10.1016/j.molimm.2013.07.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Accepted: 07/08/2013] [Indexed: 11/17/2022]
Abstract
The IgE antibody plays a central role in allergic disease. Binding of IgE to the B-cell receptor CD23 regulates IgE synthesis. Seven crystal forms of the IgE-binding head domain of CD23 have been analyzed and compared. The thirty-five independent structures reveal conformational plasticity in two IgE-binding loops.
IgE antibodies play a central role in allergic disease. They recognize allergens via their Fab regions, whilst their effector functions are controlled through interactions of the Fc region with two principal cell surface receptors, FcɛRI and CD23. Crosslinking of FcɛRI-bound IgE on mast cells and basophils by allergen initiates an immediate inflammatory response, while the interaction of IgE with CD23 on B-cells regulates IgE production. We have determined the structures of the C-type lectin “head” domain of CD23 from seven crystal forms. The thirty-five independent structures reveal extensive conformational plasticity in two loops that are critical for IgE binding.
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MESH Headings
- B-Lymphocytes/immunology
- B-Lymphocytes/metabolism
- Binding Sites/immunology
- Crystallography, X-Ray
- Humans
- Immunoglobulin E/chemistry
- Immunoglobulin E/immunology
- Immunoglobulin E/metabolism
- Models, Molecular
- Protein Binding/immunology
- Protein Conformation
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Receptors, Antigen, B-Cell/chemistry
- Receptors, Antigen, B-Cell/immunology
- Receptors, Antigen, B-Cell/metabolism
- Receptors, IgE/chemistry
- Receptors, IgE/immunology
- Receptors, IgE/metabolism
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Yuan D, Keeble AH, Hibbert RG, Fabiane S, Gould HJ, McDonnell JM, Beavil AJ, Sutton BJ, Dhaliwal B. Ca2+-dependent structural changes in the B-cell receptor CD23 increase its affinity for human immunoglobulin E. J Biol Chem 2013; 288:21667-77. [PMID: 23775083 PMCID: PMC3724626 DOI: 10.1074/jbc.m113.480657] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
Immunoglobulin E (IgE) antibodies play a fundamental role in allergic disease and are a target for therapeutic intervention. IgE functions principally through two receptors, FcϵRI and CD23 (FcϵRII). Minute amounts of allergen trigger mast cell or basophil degranulation by cross-linking IgE-bound FcϵRI, leading to an inflammatory response. The interaction between IgE and CD23 on B-cells regulates IgE synthesis. CD23 is unique among Ig receptors in that it belongs to the C-type (calcium-dependent) lectin-like superfamily. Although the interaction of CD23 with IgE is carbohydrate-independent, calcium has been reported to increase the affinity for IgE, but the structural basis for this activity has previously been unknown. We have determined the crystal structures of the human lectin-like head domain of CD23 in its Ca2+-free and Ca2+-bound forms, as well as the crystal structure of the Ca2+-bound head domain of CD23 in complex with a subfragment of IgE-Fc consisting of the dimer of Cϵ3 and Cϵ4 domains (Fcϵ3-4). Together with site-directed mutagenesis, the crystal structures of four Ca2+ ligand mutants, isothermal titration calorimetry, surface plasmon resonance, and stopped-flow analysis, we demonstrate that Ca2+ binds at the principal and evolutionarily conserved binding site in CD23. Ca2+ binding drives Pro-250, at the base of an IgE-binding loop (loop 4), from the trans to the cis configuration with a concomitant conformational change and ordering of residues in the loop. These Ca2+-induced structural changes in CD23 lead to additional interactions with IgE, a more entropically favorable interaction, and a 30-fold increase in affinity of a single head domain of CD23 for IgE. Taken together, these results suggest that binding of Ca2+ brings an extra degree of modulation to CD23 function.
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Davies AM, Rispens T, den Bleker TH, McDonnell JM, Gould HJ, Aalberse RC, Sutton BJ. Crystal structure of the human IgG4 C(H)3 dimer reveals the role of Arg409 in the mechanism of Fab-arm exchange. Mol Immunol 2012; 54:1-7. [PMID: 23164605 DOI: 10.1016/j.molimm.2012.10.029] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Revised: 10/16/2012] [Accepted: 10/18/2012] [Indexed: 12/20/2022]
Abstract
Antibodies of the human IgG4 subclass uniquely undergo a process of Fab-arm exchange in which the heavy-chains of antibodies of different specificities can dissociate and then recombine. The mechanism by which the resulting functionally monovalent but bi-specific antibodies are formed is not only key to understanding their biological role, but is also important for the design of therapeutic monoclonal antibodies. Both the hinge region and the C(H)3 domain interface are known to be involved, and of the residues that differ between human IgG1 and IgG4 in C(H)3, residue 409, the only difference at the interface itself, has been implicated. We report the high resolution (1.8Å) structure of the C(H)3 domain dimer of IgG4, and find that Arg409 in IgG4, when compared with Lys409 observed in high resolution IgG1 structures, disrupts a network of water-mediated hydrogen bonding that is conserved in IgG1. Other conformational differences were detected that are a consequence of the presence of Arg409, such as a widening of the separation between residues Asn390 in one domain and Ser 400 in the other, which opens up a groove at the edge of the interface in IgG4 compared with IgG1. The effect of all these differences on the C(H)3 interface, doubled as a result of the interface's two-fold symmetry, is weakening of the inter-domain interaction in IgG4 compared with IgG1. This suggests a mechanism by which Arg409 weakens the C(H)3 interface in IgG4, predisposing this human antibody subclass to Fab-arm exchange.
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Abstract
Aggressive angiomyxoma is a rare mesenchymal tumor that most commonly arises in the vulvovaginal region, perineum, and pelvis of women. The term aggressive emphasizes the often infiltrative nature of the tumor and its frequent association with local recurrence. Patients often present with nonspecific symptoms which are frequently misdiagnosed with more common entities, such as a Bartholin cyst, lipoma, or hernia. Histologic examination reveals a hypocellular and highly vascular tumor with a myxoid stroma containing cytologically bland stellate or spindled cells. The tumor cells are characteristically positive for estrogen and progesterone receptors, suggesting a hormonal role in the development of the tumor. Chromosomal translocation of the 12q13-15 band involving the HMGA2 gene has been described. Surgical excision is the treatment of choice, although treatment with gonadotropin-releasing hormone agonists is an emerging therapy. Metastases are exceedingly rare, and overall, the prognosis is good.
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Borthakur S, Hibbert RG, Pang MOY, Yahya N, Bax HJ, Kao MW, Cooper AM, Beavil AJ, Sutton BJ, Gould HJ, McDonnell JM. Mapping of the CD23 binding site on immunoglobulin E (IgE) and allosteric control of the IgE-Fc epsilonRI interaction. J Biol Chem 2012; 287:31457-61. [PMID: 22815482 PMCID: PMC3438978 DOI: 10.1074/jbc.c112.397059] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
IgE, the antibody that mediates allergic responses, acts as part of a self-regulating protein network. Its unique effector functions are controlled through interactions of its Fc region with two cellular receptors, FcεRI on mast cells and basophils and CD23 on B cells. IgE cross-linked by allergen triggers mast cell activation via FcεRI, whereas IgE-CD23 interactions control IgE expression levels. We have determined the CD23 binding site on IgE, using a combination of NMR chemical shift mapping and site-directed mutagenesis. We show that the CD23 and FcεRI interaction sites are at opposite ends of the Cε3 domain of IgE, but that receptor binding is mutually inhibitory, mediated by an allosteric mechanism. This prevents CD23-mediated cross-linking of IgE bound to FcεRI on mast cells and resulting antigen-independent anaphylaxis. The mutually inhibitory nature of receptor binding provides a degree of autonomy for the individual activities mediated by IgE-FcεRI and IgE-CD23 interactions.
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Hunt J, Keeble AH, Dale RE, Corbett MK, Beavil RL, Levitt J, Swann MJ, Suhling K, Ameer-Beg S, Sutton BJ, Beavil AJ. A fluorescent biosensor reveals conformational changes in human immunoglobulin E Fc: implications for mechanisms of receptor binding, inhibition, and allergen recognition. J Biol Chem 2012; 287:17459-17470. [PMID: 22442150 PMCID: PMC3366799 DOI: 10.1074/jbc.m111.331967] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Revised: 03/08/2012] [Indexed: 11/06/2022] Open
Abstract
IgE binding to its high affinity receptor FcεRI on mast cells and basophils is a key step in the mechanism of allergic disease and a target for therapeutic intervention. Early indications that IgE adopts a bent structure in solution have been confirmed by recent x-ray crystallographic studies of IgEFc, which further showed that the bend, contrary to expectation, is enhanced in the crystal structure of the complex with receptor. To investigate the structure of IgEFc and its conformational changes that accompany receptor binding in solution, we created a Förster resonance energy transfer (FRET) biosensor using biologically encoded fluorescent proteins fused to the N- and C-terminal IgEFc domains (Cε2 and Cε4, respectively) together with the theoretical basis for quantitating its behavior. This revealed not only that the IgEFc exists in a bent conformation in solution but also that the bend is indeed enhanced upon FcεRI binding. No change in the degree of bending was seen upon binding to the B cell receptor for IgE, CD23 (FcεRII), but in contrast, binding of the anti-IgE therapeutic antibody omalizumab decreases the extent of the bend, implying a conformational change that opposes FcεRI engagement. HomoFRET measurements further revealed that the (Cε2)(2) and (Cε4)(2) domain pairs behave as rigid units flanking the conformational change in the Cε3 domains. Finally, modeling of the accessible conformations of the two Fab arms in FcεRI-bound IgE revealed a mutual exclusion not seen in IgG and Fab orientations relative to the membrane that may predispose receptor-bound IgE to cross-linking by allergens.
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Offermann DA, McKendrick JE, Sejberg JJP, Mo B, Holdom MD, Helm BA, Leatherbarrow RJ, Beavil AJ, Sutton BJ, Spivey AC. Synthesis and incorporation into cyclic peptides of tolan amino acids and their hydrogenated congeners: construction of an array of A-B-loop mimetics of the Cε3 domain of human IgE. J Org Chem 2012; 77:3197-214. [PMID: 22397517 DOI: 10.1021/jo202604q] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The disruption of the human immunolobulin E-high affinity receptor I (IgE-FcεRI) protein-protein interaction (PPI) is a validated strategy for the development of anti asthma therapeutics. Here, we describe the synthesis of an array of conformationally constrained cyclic peptides based on an epitope of the A-B loop within the Cε3 domain of IgE. The peptides contain various tolan (i.e., 1,2-biarylethyne) amino acids and their fully and partially hydrogenated congeners as conformational constraints. Modest antagonist activity (IC(50) ∼660 μM) is displayed by the peptide containing a 2,2'-tolan, which is the one predicted by molecular modeling to best mimic the conformation of the native A-B loop epitope in IgE.
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49
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Cooper AM, Hobson PS, Jutton MR, Kao MW, Drung B, Schmidt B, Fear DJ, Beavil AJ, McDonnell JM, Sutton BJ, Gould HJ. Soluble CD23 controls IgE synthesis and homeostasis in human B cells. THE JOURNAL OF IMMUNOLOGY 2012; 188:3199-207. [PMID: 22393152 DOI: 10.4049/jimmunol.1102689] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
CD23, the low-affinity receptor for IgE, exists in membrane and soluble forms. Soluble CD23 (sCD23) fragments are released from membrane (m)CD23 by the endogenous metalloprotease a disintegrin and metalloprotease 10. When purified tonsil B cells are incubated with IL-4 and anti-CD40 to induce class switching to IgE in vitro, mCD23 is upregulated, and sCD23 accumulates in the medium prior to IgE synthesis. We have uncoupled the effects of mCD23 cleavage and accumulation of sCD23 on IgE synthesis in this system. We show that small interfering RNA inhibition of CD23 synthesis or inhibition of mCD23 cleavage by an a disintegrin and metalloprotease 10 inhibitor, GI254023X, suppresses IL-4 and anti-CD40-stimulated IgE synthesis. Addition of a recombinant trimeric sCD23 enhances IgE synthesis in this system. This occurs even when endogenous mCD23 is protected from cleavage by GI254023X, indicating that IgE synthesis is positively controlled by sCD23. We show that recombinant trimeric sCD23 binds to cells coexpressing mIgE and mCD21 and caps these proteins on the B cell membrane. Upregulation of IgE by sCD23 occurs after class-switch recombination, and its effects are isotype-specific. These results suggest that mIgE and mCD21 cooperate in the sCD23-mediated positive regulation of IgE synthesis on cells committed to IgE synthesis. Feedback regulation may occur when the concentration of secreted IgE becomes great enough to allow binding to mCD23, thus preventing further release of sCD23. We interpret these results with the aid of a model for the upregulation of IgE by sCD23.
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Carr JL, Sejberg JJP, Saab F, Holdom MD, Davies AM, White AJP, Leatherbarrow RJ, Beavil AJ, Sutton BJ, Lindell SD, Spivey AC. Synthesis of the C19 methyl ether of aspercyclide A via germyl-Stille macrocyclisation and ELISA evaluation of both enantiomers following optical resolution. Org Biomol Chem 2011; 9:6814-24. [PMID: 21845261 DOI: 10.1039/c1ob05862b] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Aspercyclide A (1) is a biaryl ether containing 11-membered macrocyclic natural product antagonist of the human IgE-FcεRI protein-protein interaction (PPI); a key interaction in the signal transduction pathway for allergic disorders such as asthma. Herein we report a novel approach to the synthesis of the C19 methyl ether of aspercyclide A, employing a Pd(0)-catalysed, fluorous-tagged alkenylgermane/arylbromide macrocyclisation (germyl-Stille reaction) as the key step, and evaluation of both enantiomers of this compound via ELISA following optical resolution by CSP-HPLC. A crystal structure for germyl hydride 27 is also reported.
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