C. Yu et al., STRUCTURES IN SOLUTION OF TOXINS FROM TAIWAN COBRA VENOM, NAJA-NAJA-ATRA, DERIVED FROM NMR-SPECTRA, Journal of toxicology. Toxin reviews, 13(3), 1994, pp. 291-315
The structures in solution of cobrotoxin and cardiotoxins isolated fro
m Taiwan cobra venom (Naja naja ah a) were determined using 2D-NMR and
simulated annealing methods. These toxins possess similar backbone co
nformations (a two- and a three-stranded antiparallel beta sheets) wit
h the emergence of three independent loops from the central core forme
d by the four disulfide bonds. Comparison of these NMR structures with
the crystal structures of their homologous toxins showed good agreeme
nt except at the segments of the turns. Even though overall similarity
is observed between the toxins, their functions are distinct and spec
ific. In cobrotoxin, the electrostatic interactions of functional site
s found in loops of the three-stranded beta sheet cause strong binding
with the receptor. In cardiotoxins, the stretches of hydrophobic resi
dues at the tip of the flexible loops, that are surrounded by positive
ly charged residues are expected to penetrate the lipid phase of the m
embrane and to form a hydrophobic cluster inside the membrane. The spa
tial distribution of the hydrophobic groups forms hydrophobic clusters
in binding with the hydrophobic moiety of phospholipids and the spati
al orientation of lysines acts as the cationic site to bind with the p
hosphate ion of phospholipids.