The Interplay of Disulfide Bonds, α-Helicity, and Hydrophobic Interactions Leads to Ultrahigh Proteolytic Stability of Peptides

The contribution of noncovalent interactions to the stability of naturally occurring peptides and proteins has been generally acknowledged, though how these can be rationally manipulated to improve the proteolytic stability of synthetic peptides remains to be explored. In this study, a platform to enhance the proteolytic stability of peptides was developed by controllably dimerizing them into a-helical dimers, connected by two disulfide bonds. This platform not only directs peptides toward an a-helical conformation but permits control of the interfacial hydrophobic interactions between the peptides of the dimer. Using two model dimeric systems constructed from the N-terminal alpha-helix of RNase A and known inhibitors for the E3 ubiquitin ligase MDM2 (and its homologue MDMX), a deeper understanding into the interplay of disulfide bonds, alpha-helicity, and hydrophobic interactions on enhanced proteolytic stability was sought out. Results reveal that all three parameters play an important role on attaining ultrahigh proteolytic resistance, a concept that can be exploited for the development of future peptide therapeutics. The understanding gained through this study will enable this strategy to be tailored to new peptides because the proposed strategy displays substantial tolerance to sequence permutation. It thus appears promising for conveniently creating prodrugs composed entirely of the therapeutic peptide itself (i.e., in the form of a dimer).