Conformational modification enhances myasthenogenicity in synthetic peptide of acetylcholine receptor alpha-subunit.
ABSTRACT The induction of myasthenia gravis depends on linked recognition of antigenic sites of acetylcholine receptor (AChR) by B-cells and T-cells. The former is conformationally restrained, and the latter is under the MHC class II restriction. We synthesized an artificially formed peptide (model peptide) by coupling the alpha 190-195 selected as B-cell site and cholinergic binding site and the alpha-107-116 selected as T-cell site and agretope with the intervening chain segment aligned as Asn-Pro-Gly-Gly (NPGG) to adopt beta-turn conformation. This model peptide, alpha 107-116-NPGG-alpha 190-195, was potently immunogenic in Lewis rats to provoke anti-peptide antibody reactive with native AChR and to induce the animal model of immunopharmacologic blockade of acetylcholine (ACh)-binding site. Low immunogenicity compared with this was found when using natural peptides predicted as sequences of B-cell site or T-cell site and the peptide synthesized by linking both without intervention of NPGG. The alpha 190-195 had no function of cholinergic binding either as a single segment or as part of the conformation-modified peptides; results suggest that the conformation modified for high immunogenicity does not assume the bioactive conformation for ACh-binding.
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ABSTRACT: We investigated the effect of the IgG from patients with myasthenia gravis (MG) on the degradation of normal rat junctional acetylcholine receptor (AChR) labeled with 125I-alpha-bungarotoxin (BuTx) and calculated the degradation rate (DR). The DR for the IgG from these patients was significantly higher than that from healthy volunteers and patients with other autoimmune diseases. For MG, DR was significantly correlated with the severity of the disease but not with anti-AChR antibody titer. DR was accelerated by IgG from patients with generalized MG whose antibody titers were in the normal range and by IgG from patients with ocular MG. These results indicate that measurement of the DR of junctional AChR in normal rats is more closely correlated with the severity of the disease than is measurement of anti-AChR antibody and that the former is a sensitive and confirmatory method for evaluating MG.Muscle & Nerve 09/1993; 16(8):840-8. · 2.31 Impact Factor
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ABSTRACT: The possible antigenicity of synaptotagmin, a synaptic vesicle protein acting as a cooperative calcium (Ca2+) receptor in exocytosis, was tested to determine whether it is involved in the induction of Lambert-Eaton myasthenic syndrome in which antibodies against voltage-dependent Ca2+ channels or related molecules play a pathogenic role. Repeated injections to Lewis rats with peptides of synaptotagmin residues 20 through 53 or 1 through 30 that are presumably exposed at the nerve terminal surface during exocytosis induced corresponding antipeptide antibodies; on immunoblots, antibodies recognized synaptotagmin that was expressed in the clonal cells. Electrophysiologically, the peptide (residues 20-53)-immunized rats showed (1) reduced acetylcholine quantal content of end-plate potential, (2) an increase in quantal content at high extracellular Ca2+ concentration, and (3) early facilitation followed by less marked depression of end-plate potential amplitude at a tetanic rate of repetitive nerve stimulation. Findings are similar to those in human Lambert-Eaton myasthenic syndrome and passively transferred Lambert-Eaton myasthenic syndrome in mice, and thus suggest that antibody to a synaptotagmin-voltage-dependent Ca2+ channel complex may be involved in the pathogenesis of Lambert-Eaton myasthenic syndrome. The peptide (residues 1-30)-immunized rats showed no electrophysiological abnormality.Annals of Neurology 02/1994; 35(1):74-80. · 11.19 Impact Factor
- Annals of the New York Academy of Sciences 07/1993; 681:168-71. · 4.38 Impact Factor