NMR AND RESTRAINED MOLECULAR-DYNAMICS STUDY OF THE 3-DIMENSIONAL SOLUTION STRUCTURE OF TOXIN FS2, A SPECIFIC BLOCKER OF THE L-TYPE CALCIUM-CHANNEL, ISOLATED FROM BLACK MAMBA VENOM
Jp. Albrand et al., NMR AND RESTRAINED MOLECULAR-DYNAMICS STUDY OF THE 3-DIMENSIONAL SOLUTION STRUCTURE OF TOXIN FS2, A SPECIFIC BLOCKER OF THE L-TYPE CALCIUM-CHANNEL, ISOLATED FROM BLACK MAMBA VENOM, Biochemistry, 34(17), 1995, pp. 5923-5937
The three-dimensional solution structure of toxin FS2, a GO-residue po
lypeptide isolated from the venom of black mamba snake (Dendroaspis po
lylepis polylepis), has been determined by nuclear magnetic resonance
spectroscopy. Using 600 NOE constraints and 55 dihedral angle constrai
nts, a set of 20 structures obtained from distance-geometry calculatio
ns was further refined by molecular dynamics calculations using a comb
ined simulated annealing-restrained MD protocol. The resulting 20 conf
ormers, taken to represent the solution structure, give an average rms
d of 1.2 Angstrom for their backbone atoms, relative to the average st
ructure. The overall resulting three-fingered structure is similar to
those already observed in several postsynaptic neurotoxins, cardiotoxi
ns, and fasciculins, which all share with toxin FS2 the same network o
f four disulfide bridges. The overall concavity of the molecule, consi
dered as a flat bottomed dish, is oriented toward the C-terminal loop
of the molecule. This orientation is similar to that of fasciculins an
d cardiotoxins but opposite to that of neurotoxins. On the basis of th
e local rms displacements between the 20 conformers, the structure of
the first loop appears to be less well defined in FS2 than in the prev
iously reported neurotoxin structures, but fasciculin 1 shows a simila
r trend with particularly high temperature factors for this part of th
e X-ray structure. The concave side which presents most of the positiv
ely charged residues is quite similar in FS2 and fasciculin 1. The mai
n difference is shown by the convex side of the third loop, mostly hyd
rophobic in FS2, in contrast to the pair of negatively charged asparta
tes in fasciculin 1. This difference could be one of the factors leadi
ng to the distinct pharmacological properties-L-type calcium channel b
locker for FS2 and cholinesterase inhibitor for fasciculins-observed f
or these two subgroups of the ''angusticeps-type'' toxins.