Structural studies of .alpha.-bungarotoxin. 1. Sequence-specific proton NMR resonance assignments

We report the complete sequence-specific assignment of the backbone resonances and most of the side-chain resonances in the 1H NMR spectrum of alpha-bungarotoxin by two-dimensional NMR. Problems with resonance overlap were resolved with the assistance of the HRNOESY experiment described in an accompanying paper Basus, V.J., & Scheek, R.M. (1988) Biochemistry (second paper of three in this issue). Significant differences exist between the solution structure described here and the crystal structure of alpha-bungarotoxin, on the basis of the proton to proton distances obtained by nuclear Overhauser enhancement spectroscopy (NOESY) and the corresponding distances from the X-ray crystal structure Love, R.A., & Stroud, R.M. (1986) Protein Eng. 1, 37. These differences include a larger beta-sheet in solution and a different orientation of the invariant tryptophan, Trp-28, making the solution structure more consistent with the crystal structure of the homologous neurotoxin alpha-cobratoxin. Four errors in the order of the amino acids in the primary sequence were indicated by the NMR data. These errors were confirmed by chemical means, as described in an accompanying paper Kosen, P.A., Finer-Moore, J., McCarthy, M.P., & Basus, V.J. (1988) Biochemistry (third paper of three in this issue).