NMR ANALYSIS REVEALS A POSITIVELY CHARGED HYDROPHOBIC DOMAIN AS A COMMON MOTIF TO BOUND ACETYLCHOLINE AND D-TUBOCURARINE

A complete H-1 assignment of d-tubocurarine was carried out using 1D a nd 2D NMR techniques. Geometries of free acetylcholine (ACh) and d-tub ocurarine were compared with those of the ligands bound to a recombina nt cholinergic binding site (Talpha184-200 expressed as a fusion prote in in Escherichia coli). The conformations of the free ligands were de termined by NOESY experiments while those of the bound molecules were obtained by transferred NOESY. The complete relaxation matrix was solv ed yielding distance constraints which were further refined by a sigma back-calculation. ACh bound to recombinant Talpha184-200 closely rese mbled the conformation previously reported for ACh bound to the intact receptor. d-Tubocurarine in the bound state undergoes extensive induc ed conformational rearrangements generating a ''cup''-shaped structure . A unique positively charged hydrophobic domain is identified as char acteristic of both bound cholinergic ligands.