The impact of the fourth disulfide bridge in scorpion toxins of the alpha-KTx6 subfamily.
Animal toxins are highly reticulated and structured polypeptides that adopt a limited number of folds. In scorpion species, the most represented fold is the alpha/beta scaffold in which an helical structure is connected to an antiparallel beta-sheet by two disulfide bridges. The intimate relationship existing between peptide reticulation and folding remains poorly understood. Here, we investigated the role of disulfide bridging on the 3D structure of HsTx1, a scorpion toxin potently active on Kv1.1 and Kv1.3 channels. This toxin folds along the classical alpha/beta scaffold but belongs to a unique family of short-chain, four disulfide-bridged toxins. Removal of the fourth disulfide bridge of HsTx1 does not affect its helical structure, whereas its two-stranded beta-sheet is altered from a twisted to a nontwisted configuration. This structural change in HsTx1 is accompanied by a marked decrease in Kv1.1 and Kv1.3 current blockage, and by alterations in the toxin to channel molecular contacts. In contrast, a similar removal of the fourth disulfide bridge of Pi1, another scorpion toxin from the same structural family, has no impact on its 3D structure, pharmacology, or channel interaction. These data highlight the importance of disulfide bridging in reaching the correct bioactive conformation of some toxins.
Carrega
Louis
L
Laboratoire d'Ingénierie des Protéines, CNRS FRE 2738, IFR Jean Roche, Faculté de Médecine Nord, Marseille Cedex, France.
Mosbah
Amor
A
Ferrat
Gilles
G
Beeton
Christine
C
Andreotti
Nicolas
N
Mansuelle
Pascal
P
Darbon
Hervé
H
De Waard
Michel
M
Sabatier
Jean-Marc
JM
D000595:Amino Acid Sequence; D000818:Animals; D004220:Disulfides / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012604:Scorpion Venoms / Q000737:chemistry* / Q000633:toxicity; D012605:Scorpions
D004220:Disulfides; D010455:Peptides; D012604:Scorpion Venoms; C109471:TX1 toxin, Heterometrus spinnifer