The Three-Dimensional NMR Solution Structure of α-Cobratoxin at pH 7.5 and Conformational Differences With the NMR Solution Structure at pH 3.2

The 3D solution structure of α-cobratoxin, a neurotoxin purified from the Naja naja siamensis snake venom, has been determined by Nuclear Magnetic Resonance spectroscopy, in conjunction with distance geometry and restrained molecular dynamics, at pH 7.5. A total of 490 distance restraints were obtained from NOE intensities and 25 φ dihedral angle restraints deduced from J- coupling data. The generated structures are well defined with root mean square deviations from a geometrical mean structure of 0.107 ± 0.036 nm for the backbone atoms and 0.128 ±0.073 nm for the side-chain atoms (considering residues 1 to 66 minus 26 to 35). A comparison between the generated structures at pH 7.5 and the mean NMR solution structure at pH 3.2 revealed that the 3D structure of α-cobratoxin is more compact at neutral pH. This major difference is mainly due to the pH-dependant conformational variations of three residues His(18), Thr(44) and Thr(59).