CONFORMATIONAL REQUIREMENTS FOR MOLECULAR RECOGNITION OF ACETYLCHOLINE-RECEPTOR MAIN IMMUNOGENIC REGION (MIR) ANALOGS BY MONOCLONAL ANTI-MIR ANTIBODY - A 2-DIMENSIONAL NUCLEAR-MAGNETIC-RESONANCE AND MOLECULAR-DYNAMICS APPROACH

The conformational properties of two [D-A70, A76] and [Aib70, A76] analogues of the alpha67-76 Torpedo acetylcholine receptor fragment, with low binding capacity for the anti main immunogenic region (MIR) antibodies, were studied in DMSO by two-dimensional nmr techniques and molecular dynamics simulations. The results were compared to the free and bound conformations of the [A76] analogue, which has twice more affinity for the anti-MIR monoclonal antibody 6 (mAb6), than the natural Torpedo sequence. It appeared that a single substitution of the A70, at a crucial position, by the D-A70 or Aib70 ,could modify completely the conformational behavior of the peptide and reduced its recognition by the anti-MIR antibody. The WNPADY rigid structure at the N-terminal part was essential for antibody recognition. The adjacent more flexible C-terminal sequence (GGIK) gives additional stability to the monoclonal antibody-peptide complex probably due to an adequate orientation of the peptide side chains in the complex, by setting them in close contact with the antibody.