NMR Solution Structure of a Two-Disulfide Derivative of Charybdotoxin: Structural Evidence for Conservation of Scorpion Toxin α/β Motif and Its Hydrophobic Side Chain Packing,

Publisher Website
Google Scholar
Abstract
The α/β scorpion fold consisting of a short α-helix and β-sheet is a structural motif common to scorpion toxins, insect defensins, and plant γ-thionins that invariably contains three disulfides. CHABII is a two-disulfide derivative of the scorpion toxin charybdotoxin (ChTX), chemically synthesized by inserting two l-α-aminobutyric acids in place of the two half-cystine residues involved in the disulfide 13−33. This disulfide is one of the two disulfides which connect the α-helix to the β-sheet. The solution structure of CHABII was determined at pH 6.3 and 5 °C using 2D NMR and simulated annealing from 513 distance and 46 dihedral angle constraints. The NMR structure of CHABII is well-defined as judged from the low value of the averaged backbone rms deviation between the 30 lowest energy structures and the energy-minimized mean structure (〈rmsd〉 = 0.65 Å for the entire sequence and 0.48 Å for the segment 3−36). Analysis and comparison of the solution structures of CHABII and ChTX lead to the following conclusions: (i) the fold of CHABII is similar to that of ChTX as indicated by the low value of the averaged backbone atomic rms deviation between the 10 lowest energy solution structures of the two proteins (1.44 Å); (ii) the packing of the hydrophobic core is well-preserved, underlying the critical structural role of the hydrophobic interactions even for such a small and cysteine-rich protein as ChTX.