Folding-Assisted Peptide Disulfide Formation and Dimerization

Abstract

Disulfide bonds form covalent bonds between distal regions of peptides and proteins to dramatically impact their folding, stability, and oligomerization. Given the prevalence of disulfide bonds in many natural products, considerable effort has been invested in site-selective disulfide bond formation approaches to control the folding of chemically synthesized peptides and proteins. Here, we show that the careful choice of thiol oxidation conditions can lead to monomeric or dimeric species from fully deprotected linear bisthiol peptides. Starting from a p53-derived peptide, we found that oxidation under aqueous (nondenaturing) conditions produces antiparallel dimers with enhanced α-helical character, while oxidation under denaturing conditions promotes formation of a nonhelical intramolecular disulfide species. Examination across peptide variants suggests that intramolecular disulfide formation is robust across diverse peptide sequences, while dimerization is sensitive to both the α-helical folding of the linear peptide and aromatic residues at the dimerization interface. All disulfide species are more resistant to protease degradation than the linear peptide but are easily reduced to restore the initial bisthiol peptide. Both disulfide formation approaches are compatible with α-helix-stabilizing cross-linkers. These results provide an approach for using disulfide bonds to control peptide folding and oligomerization to better understand how folding influences interactions with diverse molecular targets.