Structure of apamin in solution: a two-dimensional nuclear magnetic resonance study

Abstract

A 2-dimensional (2-D) Fourier-transform NMR study of the 18 amino acid neurotoxin apamin isolated from honeybee venom is reported. Combining 2-D J-correlated spectra with 2-D nuclear Overhauser spectra in H2O solution permits essentially complete assignment of the 1H NMR spectrum of apamin at a fixed pH, including a number of spin systems that are reported for the 1st time. The structural model previously derived by Bystrova, et al. from NMR data is shown to be largely correct. The 2-D nuclear Overhauser effect (NOE) spectrum in particular reveals a series of amide-amide NOE consistent with an .alpha.-helical core (residues 9-15) in the molecule. NOE between amide and C.alpha. protons, followed by amide to amide NOE, indicate a .beta.-turn involving residues 3-5 and a nonstandard turn including residues 6-8. No evidence was found for the .beta.-type structure postulated at the C terminus, however. Instead, it appears that the .alpha.-helix continues with increasing fraying from residues 16-18.