Differential Self-Assembly Behaviors and Proteolytic Stability of Bicyclic Peptides Compared to Monocyclic Peptides

Self-assembling cyclic peptides exhibit several advantages over their linear counterparts; however, the structural simplicity of monocyclic peptides (MCPs) limits their further development into assemblies with more elaborate and complex functions. Here, we demonstrate that bicyclic peptides (BCPs) offer significant potential for constructing peptide assemblies with enhanced controllability and proteolytic stability. Two types of amphiphilic BCPs were designed: one featuring a horizontal division of a monocycle into separate polar and nonpolar cycles (an 8-shaped bicycle), and the other involving a vertical division into two independent amphiphilic cycles (a ∞-shaped bicycle). This orientational orthogonality in bicyclization critically affects the molecular conformation and rigidity of BCPs, which in turn influence nanostructural features of the resulting assemblies, such as surface charge density. Notably, the BCPs exhibited nearly 100% proteolytic stability, despite being composed entirely of natural L-amino acids. In contrast, the corresponding MCP showed only 3% stability under the same experimental conditions. The enhanced functionality of BCPs, combined with the redox-responsive nature of our design, enables the construction of protease-resistant peptide nanoassemblies with high structural complexity and functions.