1
|
Trinh VB, Foster AJ, Fairclough RH. Design, synthesis, and characterization of a 39 amino acid peptide mimic of the main immunogenic region of the Torpedo acetylcholine receptor. Mol Immunol 2014; 59:79-90. [PMID: 24491490 DOI: 10.1016/j.molimm.2014.01.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Accepted: 01/04/2014] [Indexed: 11/16/2022]
Abstract
We have designed a 39 amino acid peptide mimic of the conformation-dependent main immunogenic region (MIR) of the Torpedo acetylcholine receptor (TAChR) that joins three discontinuous segments of the Torpedo α-subunit, α(1-12), α(65-79), and α(110 - 115) with two GS linkers: This 39MIR-mimic was expressed in E. coli as a fusion protein with an intein-chitin-binding domain (IChBD) to permit affinity collection on chitin beads. Six MIR-directed monoclonal antibodies (mAbs) bind to this complex and five agonist/antagonist site directed mAbs do not. The complex of MIR-directed mAb-132A with 39MIR has a Kd of (2.11±0.11)×10(-10)M, which is smaller than (7.13±1.20)×10(-10)M for the complex of mAb-132A with α(1-161) and about the same as 3.4×10(-10)M for that of mAb-132A with TAChR. Additionally, the 39MIR-IChBD adsorbs all MIR-directed antibodies (Abs) from an experimental autoimmune myasthenia gravis (EAMG) rat serum. Hence, the 39MIR-mimic has the potential to inactivate or remove pathogenic Torpedo MIR-directed Abs from EAMG sera and to direct a magic bullet to the memory B-cells that produce those pathogenic Abs. The hope is to use this as a guide to produce a mimic of the human MIR on the way to an antigen specific therapeutic agent to treat MG.
Collapse
Affiliation(s)
- Vu B Trinh
- University of California, Davis-School of Medicine, Department of Neurology, One Shields Ave., 1515 Newton Ct. Room 510C, Davis, CA 95616, USA; Biochemistry and Molecular Biology Graduate Group and Biochemistry Molecular Cellular and Developmental Biology Graduate Group of UC Davis, Davis, CA 95616, USA
| | - Alex J Foster
- University of California, Davis-School of Medicine, Department of Neurology, One Shields Ave., 1515 Newton Ct. Room 510C, Davis, CA 95616, USA; Biochemistry and Molecular Biology Graduate Group and Biochemistry Molecular Cellular and Developmental Biology Graduate Group of UC Davis, Davis, CA 95616, USA
| | - Robert H Fairclough
- University of California, Davis-School of Medicine, Department of Neurology, One Shields Ave., 1515 Newton Ct. Room 510C, Davis, CA 95616, USA; Biochemistry and Molecular Biology Graduate Group and Biochemistry Molecular Cellular and Developmental Biology Graduate Group of UC Davis, Davis, CA 95616, USA.
| |
Collapse
|
2
|
Morell SW, Trinh VB, Gudipati E, Friend A, Page NA, Agius MA, Richman DP, Fairclough RH. Structural characterization of the main immunogenic region of the Torpedo acetylcholine receptor. Mol Immunol 2013; 58:116-31. [PMID: 24333757 DOI: 10.1016/j.molimm.2013.11.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Revised: 11/06/2013] [Accepted: 11/07/2013] [Indexed: 11/27/2022]
Abstract
To develop antigen-specific immunotherapies for autoimmune diseases, knowledge of the molecular structure of targeted immunological hotspots will guide the production of reagents to inhibit and halt production of antigen specific attack agents. To this end we have identified three noncontiguous segments of the Torpedo nicotinic acetylcholine receptor (AChR) α-subunit that contribute to the conformationally sensitive immunological hotspot on the AChR termed the main immunogenic region (MIR): α(1-12), α(65-79), and α(110-115). This region is the target of greater than 50% of the anti-AChR Abs in serum from patients with myasthenia gravis (MG) and animals with experimental autoimmune myasthenia gravis (EAMG). Many monoclonal antibodies (mAbs) raised in one species against an electric organ AChR cross react with the neuromuscular AChR MIR in several species. Probing the Torpedo AChR α-subunit with mAb 132A, a disease inducing anti-MIR mAb raised against the Torpedo AChR, we have determined that two of the three MIR segments, α(1-12) and α(65-79), form a complex providing the signature components recognized by mAb 132A. These two segments straddle a third, α(110-115), that seems not to contribute specific side chains for 132A recognition, but is necessary for optimum antibody binding. This third segment appears to form a foundation upon which the three-dimensional 132A epitope is anchored.
Collapse
Affiliation(s)
- Stuart W Morell
- University of California, Davis School of Medicine, Department of Neurology, One Shields Avenue, 1515 Newton Court, Room 510C, Davis, CA 95616, United States; Biochemistry, Molecular, Cellular, and Developmental Biology Graduate Group of UC Davis, United States
| | - Vu B Trinh
- University of California, Davis School of Medicine, Department of Neurology, One Shields Avenue, 1515 Newton Court, Room 510C, Davis, CA 95616, United States; Biochemistry, Molecular, Cellular, and Developmental Biology Graduate Group of UC Davis, United States
| | - Eswari Gudipati
- Biochemistry, Siemens Healthcare Diagnostics, 5210 Pacific Concourse Drive, Los Angeles, CA 90045, United States
| | - Alexander Friend
- University of California, Davis School of Medicine, Department of Neurology, One Shields Avenue, 1515 Newton Court, Room 510C, Davis, CA 95616, United States
| | - Nelson A Page
- University of California, Davis School of Medicine, Department of Neurology, One Shields Avenue, 1515 Newton Court, Room 510C, Davis, CA 95616, United States; Department of Physics Graduate Program, University of California, Davis, One Shields Avenue, Davis, CA 95616, United States
| | - Mark A Agius
- University of California, Davis School of Medicine, Department of Neurology, One Shields Avenue, 1515 Newton Court, Room 510C, Davis, CA 95616, United States; VANCHCS, 10535 Hospital Way, Mather, CA 95655, United States
| | - David P Richman
- University of California, Davis School of Medicine, Department of Neurology, One Shields Avenue, 1515 Newton Court, Room 510C, Davis, CA 95616, United States; Neurosciences Graduate Group of UC Davis, United States
| | - Robert H Fairclough
- University of California, Davis School of Medicine, Department of Neurology, One Shields Avenue, 1515 Newton Court, Room 510C, Davis, CA 95616, United States; Biochemistry, Molecular, Cellular, and Developmental Biology Graduate Group of UC Davis, United States; Biophysics Graduate Group of UC Davis, United States.
| |
Collapse
|
3
|
Abstract
The synapse is a localized neurohumoral contact between a neuron and an effector cell and may be considered the quantum of fast intercellular communication. Analogously, the postsynaptic neurotransmitter receptor may be considered the quantum of fast chemical to electrical transduction. Our understanding of postsynaptic receptors began to develop about a hundred years ago with the demonstration that electrical stimulation of the vagus nerve released acetylcholine and slowed the heart beat. During the past 50 years, advances in understanding postsynaptic receptors increased at a rapid pace, owing largely to studies of the acetylcholine receptor (AChR) at the motor endplate. The endplate AChR belongs to a large superfamily of neurotransmitter receptors, called Cys-loop receptors, and has served as an exemplar receptor for probing fundamental structures and mechanisms that underlie fast synaptic transmission in the central and peripheral nervous systems. Recent studies provide an increasingly detailed picture of the structure of the AChR and the symphony of molecular motions that underpin its remarkably fast and efficient chemoelectrical transduction.
Collapse
Affiliation(s)
- Steven M Sine
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
| |
Collapse
|
4
|
Fairclough RH, Agius MA, Gudipati E, Silvian L, Hamaoka B, Beltzner CC, Lin MY, Chuang AR, Richman DP. Agonist-Induced Transitions of the Acetylcholine Receptor. Ann N Y Acad Sci 2003; 998:101-13. [PMID: 14592867 DOI: 10.1196/annals.1254.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Anti-acetylcholine receptor (AChR) monoclonal antibody 383C binds to the beta-hairpin loop alpha(187-199) of only one of the two Torpedo AChR alpha subunits. The loop recognized is associated with the alpha subunit corresponding to the high-affinity d-tubocurarine (dTC) binding site. Desensitization of the receptor with carbamylcholine completely blocks the binding of 383C. Mild reduction of AChR alpha subunit cys 192-193 disulfide with DTT and subsequent reaction with 5-iodoacetamidofluorescein label only the high-affinity dTC alpha subunit. Rhodamine-labeled alpha-bungarotoxin (R-Btx) binds to the unlabeled AChR alpha subunit as monitored by fluorescence resonance energy transfer between the fluorescein and rhodamine dyes. A 10-A contraction of the distance between the dyes is observed following the addition of carbamylcholine. In a small angle X-ray diffraction experiment exploiting anomalous X-ray scattering from Tb(III) ions titrated into AChR Ca(II) binding sites, we find evidence for a change in the Tb(III) ion distribution in the region of the ion channel following addition of carbamylcholine to the AChR. The carbamylcholine-induced loss of the 383C epitope, the 10-A contraction of the beta-hairpin loop, and the loss of multivalent cations from the channel likely represent the first molecular transitions leading to AChR channel opening.
Collapse
Affiliation(s)
- Robert H Fairclough
- Department of Neurology, University of California, Davis, Davis, California 95616, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
5
|
Abstract
Muscle nicotinic acetylcholine receptors (AChRs) are pentamers that contain two alpha subunits a beta, gamma (or epsilon), and delta subunit. In this paper, we have characterized subunit processing and folding events leading to formation of the two AChR ligand binding sites. alpha subunit residues, 187-199, which are part of overlapping ACh and alpha-bungarotoxin (Bgt) binding sites on AChRs, were assayed using a monoclonal antibody (mAb) specific for these residues. We found that this region was inaccessible to the mAb early during AChR assembly but became accessible as the first of two Bgt binding sites formed later during assembly, indicating that the region changes conformation as the Bgt binding site appears. Without previous reduction, 20% of the alpha subunits could be alkylated by bromoacetylcholine bromide as the first ACh binding site formed, which further indicated that the disulfide bond between cysteines 192 and 193 does not form until the first ACh binding site appears soon after Bgt binding site formation. When alpha subunits were mutated to add a glycosylation site at residue 187, the number of Bgt binding sites increased threefold, AChRs assembled more efficiently, and 2.5-fold more AChRs reached the cell surface. Our results indicate that binding site formation involves a rate-limiting rearrangement of the alpha subunit that exposes the 187-199 region to the endoplasmic reticulum lumen and determines when cysteines 192 and 193 disulfide bond.
Collapse
|
6
|
Abstract
Much progress has been made in the 26 years since initial studies of the first purified acetylcholine receptors (AChRs) led to the discovery that an antibody-mediated autoimmune response to AChRs causes the muscular weakness and fatigability characteristic of myasthenia gravis (MG) and its animal model, experimental autoimmune myasthenia gravis (EAMG). Now, the structure of muscle AChRs is much better known. Monoclonal antibodies to muscle AChRs, developed as model autoantibodies for studies of EAMG, were used for initial purifications of neuronal AChRs, and now many homologous subunits of neuronal nicotinic AChRs have been cloned. There is a basic understanding of the pathological mechanisms by which autoantibodies to AChRs impair neuromuscular transmission. Immunodiagnostic assays for MG are used routinely. Nonspecific approaches to immunosuppressive therapy have been refined. However, fundamental mysteries remain regarding what initiates and sustains the autoimmune response to muscle AChRs and how to specifically suppress this autoimmune response using a practical therapy. Many rare congenital myasthenic syndromes have been elegantly shown to result from mutations in muscle AChRs. These studies have provided insights into AChR structure and function as well as into the pathological mechanisms of these diseases. Evidence has been found for autoimmune responses even to some central nervous system neurotransmitter receptors, but only one neuronal AChR has so far been implicated in an autoimmune disease. Thus far, only two neuronal AChR mutations have been found to be associated with a rare form of epilepsy, but many more neuronal AChR mutations will probably be found to be associated with disease in the years ahead.
Collapse
Affiliation(s)
- J M Lindstrom
- Department of Neuroscience, Medical School of the University of Pennsylvania, Philadelphia, Pennsylvania 19104-6074, USA.
| |
Collapse
|
7
|
Fairclough RH, Twaddle GM, Gudipati E, Stone RJ, Richman DP, Burkwall DA, Josephs R. Mapping the mAb 383C epitope to alpha 2(187-199) of the Torpedo acetylcholine receptor on the three-dimensional model. J Mol Biol 1998; 282:301-15. [PMID: 9735289 DOI: 10.1006/jmbi.1998.2000] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Monoclonal antibody 383C is an anti-acetylcholine receptor antibody whose binding to the receptor is blocked by alpha-bungarotoxin and by carbamylcholine. Monoclonal antibody 383C binds to the alpha subunit of the Torpedo acetylcholine (ACh) receptor as well as to its V8-protease 20 kDa fragment that possesses the affinity alkylatable Cys192/193. In an epitope scanning experiment spanning the N-terminal 211 amino acid residues of the alpha subunit, 383C binds uniquely to three overlapping peptides; alpha(184-196), alpha(187-199) and alpha(190-202). These peptides span a cluster of amino acid residues implicated in the binding of acetylcholine, including Cys192/193. To map the location of these residues on the three-dimensional model of the ACh receptor, we have employed a combination of X-ray diffraction from oriented complexes of 383C with ACh receptor-enriched membrane vesicles and electron microscopy of negatively stained tubular arrays of 383C/receptor complexes. The X-ray diffraction study finds extra electron density in the presence of 383C centered 35 A above the synaptic side phosphate head groups. The electron micrographic images display extra stain exclusion from the antibody at a site adjacent to the alpha2 subunit on the periphery of the rosette clockwise to the alpha2 vertex. This mapping localizes several residues of the ACh receptor alpha subunit involved in the binding of acetylcholine. Despite these residues being present in both alpha subunits, only the alpha2 subunit is decorated with this monoclonal antibody.
Collapse
Affiliation(s)
- R H Fairclough
- Department of Neurology, University of California Davis, Davis, CA, 95616, USA
| | | | | | | | | | | | | |
Collapse
|
8
|
Lin MY, Twaddle GM, Gudipati E, Fairclough RH. Measurement of the dissociation rate constants of alpha-bungarotoxin from the acetylcholine receptor low- and high-affinity tubocurarine sites. Ann N Y Acad Sci 1998; 841:108-10. [PMID: 9668228 DOI: 10.1111/j.1749-6632.1998.tb10916.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M Y Lin
- Department of Neurology, University of California, Davis 95616, USA
| | | | | | | |
Collapse
|
9
|
Lin MY, Twaddle GM, Gudipati E, Richman DP, Fairclough RH. MAb 383C binds to the alpha-subunit of the acetylcholine receptor associated with the high-affinity tubocurarine site. Ann N Y Acad Sci 1998; 841:101-3. [PMID: 9668226 DOI: 10.1111/j.1749-6632.1998.tb10914.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M Y Lin
- Department of Neurology, University of California, Davis 95616, USA
| | | | | | | | | |
Collapse
|
10
|
Fairclough RH, Gudipati E, Lin MY, Twaddle GM, Richman DP, Burkwall DA, Josephs R. A role for alpha(187-199) in the conversion of agonist binding energy to the opening of the acetylcholine receptor ion channel. Ann N Y Acad Sci 1998; 841:87-92. [PMID: 9668223 DOI: 10.1111/j.1749-6632.1998.tb10911.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- R H Fairclough
- Department of Neurology, University of California, Davis 95616, USA
| | | | | | | | | | | | | |
Collapse
|