Localization of the main immunogenic region of human muscle acetylcholine receptor to residues 67-76 of the alpha subunit.

Abstract

The majority of antibodies to the acetylcholine receptor (AcChoR), both in the human disease myasthenia gravis and in its experimental models, are directed against an extracellular area of the AcChoR a subunit called the main immunogenic region (MIR). We have studied the binding of anti-AcChoR monoclonal antibodies (mAbs) to 26 synthetic peptides corresponding to the hydrophilic parts of the human AcChoR a subunit. The binding sites for eight anti-MIR mAbs and for eight anti-a-subunit, non-anti-MiIR mAbs were localized. Anti-MIR mAbs bound to one peptide corresponding to residues 63-80 of the human a subunit. A second panel of peptides corresponding to the various parts of the a-subunit segment 63-80 was synthesized. Anti-MIR antibodies bound to a peptide that contained the a-subunit sequence 67-76. Thus, a main constituent loop of the MIR is localized between residues 67 and 76 of the a subunit.

Crystallization and preliminary crystallographic study of an Fab fragment of a pathogenic rat monoclonal antibody against the nicotinic acetylcholine receptor

“…Anti-MIR mAb binding has been localized between amino acid residues 67 and 76 of the a-subunit of Torpedo (WNPADYGGIK) and human (WNPDDYGGVK) AChR (Tzartos et al, 1988(Tzartos et al, , 1990). Peptide analogue studies revealed the antigenic role of each residue within 67-76; the segment 67-71 proved the most critical and sufficient for mAb binding (Papadouli et al, 1993).…”

“…Its dissociation constant (Kd) for human muscle AChR is 21.6 nM, and for Torpedo AChR it is 1.8 nM. Its exact epitope on both the Torpedo and human AChR has been identified (67-76 [Tzartos et al, 1988[Tzartos et al, , 1990Papadouli et al, 19931). Like other anti-MIR mAbs, it causes antigenic modulation of AChR on animal and human muscle cell cultures, while its Fab fragments very efficiently protect the AChR against degradation caused by the MG sera (Tzartos et al, 1985;Sophianos & Tzartos, 1989).…”

Expression of Soluble Ligand- and Antibody-binding Extracellular Domain of Human Muscle Acetylcholine Receptor α Subunit in Yeast Pichia pastoris

“…The N-terminal extracellular domain of the ␣ chain (␣-(1-210)) contains both the binding sites for cholinergic ligands (4) and the MIR, the major target for autoantibodies in both MG and experimental models of MG (5-7). The major loop of the overlapping epitopes for several anti-MIR monoclonal antibodies (mAbs) has been localized between residues 67 and 76 of the ␣ subunit (8,9). Previous experiments have shown that the binding sites for both acetylcholine and ␣-BTX are located close to two adjacent cysteine residues at positions 192 and 193 of the ␣ subunit (10).…”

A Novel Fusion Protein, AChR-Fc, Ameliorates Myasthenia Gravis by Neutralizing Antiacetylcholine Receptor Antibodies and Suppressing Acetylcholine Receptor-Reactive B Cells

“…The binding of ACh to the receptor leads to opening of ion channels, which allows Na + to flow into the muscle, leading to increased concentrations of Ca 2+ in the muscle, and triggering muscle contraction. Tzartos et al [12] reported that the many AChR antibodies bind to a region of the receptor α subunit, called the main immunogenic region. From these findings, we considered that inhibition of antibodies to the AChR α subunit In the present study, we created AChR-Fc, and examined its effects on autoantibody production and autoantibodyproducing cells.…”