3-DIMENSIONAL STRUCTURE OF A GAMMA-CARBOXYGLUTAMIC ACID-CONTAINING CONOTOXIN, CONANTOKIN-G, FROM THE MARINE SNAIL CONUS-GEOGRAPHUS - THE METAL-FREE CONFORMER
Ac. Rigby et al., 3-DIMENSIONAL STRUCTURE OF A GAMMA-CARBOXYGLUTAMIC ACID-CONTAINING CONOTOXIN, CONANTOKIN-G, FROM THE MARINE SNAIL CONUS-GEOGRAPHUS - THE METAL-FREE CONFORMER, Biochemistry, 36(23), 1997, pp. 6906-6914
Conantokin G is a gamma-carboxyglutamic acid-containing conotoxin from
the venom of the marine cone snail Conus geographus. The 17-residue p
eptide, which contains five gamma-carboxyglutamic acid (Gla) residues
and an amidated C-terminal asparagine amide, was synthesized chemicall
y in a form identical to the natural conantokin G. To gain insight int
o the role of gamma-carboxyglutamic acid in the structure of this pept
ide, we determined the three-dimensional structure of conantokin G by
H-1 NMR and compared its structure to other conotoxins and to the gamm
a-carboxyglutamic acid-containing regions of the vitamin K-dependent b
lood-clotting proteins. Complete resonance assignments were made by tw
o-dimensional H-1 NMR spectroscopy in the absence of metal ions. NOE c
ross-peaks d(alpha N), d(NN), and d(beta N) provided interproton dista
nce information, and vicinal spin-spin coupling constants (3)J(HN alph
a), were used to calculate phi torsion angles. Distance geometry and s
imulated annealing methods were used to derive 20 convergent structure
s from a set of 227 interproton distance restraints and 13 torsion ang
le measurements. The backbone rmsd to the geometric average for 20 fin
al structures is 0.8 +/- 0.1 Angstrom. Conantokin G consists of a stru
ctured region commencing at Gla 3 and extending through arginine 13. T
his structure includes a partial loop centered around Gla 3 and Gla 4,
a distorted type I turn between glutamine 6 and glutamine 9, and two
type I turns involving Gla 10, leucine 11, and isoleucine 12 and argin
ine 13. Together, these two turns define approximately 1.6 turns of a
distorted 3(10) helix. The observed structure possesses structural ele
ments similar to those seen in the disulfide-linked conotoxins.