R. Bhaskaran et al., CARDIOTOXIN-II FROM TAIWAN COBRA VENOM, NAJA-NAJA-ATRA - STRUCTURE INSOLUTION AND COMPARISON AMONG HOMOLOGOUS CARDIOTOXINS, The Journal of biological chemistry, 269(38), 1994, pp. 23500-23508
The three-dimensional structure in solution of cardiotoxin II, a membr
ane toxin from the venom of Taiwan cobra, Naja naja atra, was determin
ed using H-1 nuclear magnetic resonance spectroscopy and molecular mod
eling based on the hybrid distance geometry/dynamic simulated annealin
g technique. A complete sequence-specific proton assignment was obtain
ed, and the secondary structures of the protein were determined from i
nformation on nuclear Overhauser effect connectivities, coupling const
ants, and hydrogen exchange were confirmed using the main-chain-direct
ed strategy. Twelve simulated annealing structures found to be within
a single family were selected based on the condition of distance const
raint violation less than 0.02 nm and the dihedral angle violation les
s than 4 degrees. The average atomic root mean square deviation betwee
n the selected structures and their geometric average are 0.079 nm for
the backbone atoms and 0.137 nm for all heavy atoms; they are 0.044 n
m and 0.117 nm, respectively, when considering the secondary structura
l residues only. The molecule adopts a compact structure consisting of
three major loops emerging from a globular head. These loops contain
five strands to form double- and a triple-stranded antiparallel beta s
heets. Comparisons are made between this structure and those of its ho
mologous cardiotoxins in order to derive further information on their
structural variations.