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

Abstract

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., and 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 enhancemenbt spectroscopy (NOESY) and the corresponding distances from the X-ray crystal structure [Love, R. A., and Stroud, R. M. (1986) Protein Eng. 1, 37]. These differences include a large .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., and Basus, V. J. (1988) Biochemistry (third paper of three in this issue)].