S. Pegoraro et al., The disulfide-coupled folding pathway of apamin as derived from diselenide-quenched analogs and intermediates, PROTEIN SCI, 8(8), 1999, pp. 1605-1613
The sequence of apamin, an 18 residue bee venom toxin, encloses all the inf
ormation required for the correct disulfide-coupled folding into the cystin
e-stabilized alpha-helical motif. Three apamin analogs, each containing a p
air of selenocysteine residues replacing the related cysteines, were synthe
sized to mimic the three possible apamin isomers with two crossed, parallel
, or consecutive disulfides, respectively. Refolding experiments clearly re
vealed that. the redox potential of selenocysteine prevails over the sequen
ce encoded structural information for proper folding of apamin. Thus, selen
ocysteine can be used as a new device to generate productive and nonproduct
ive folding intermediates of peptides and proteins. In fact, disulfides are
selectively reduced in presence of the diselenide and the conformational f
eatures derived from these intermediates as well as from the three-dimensio
nal (3D) structures of the selenocysteine-containing analogs with their non
natural networks of diselenide/disulfide bridges allowed to gain further in
sight into the subtle driving forces for the correct folding of apamin that
mainly derive from local conformational preferences.