Helicity-Dependent Enzymatic Peptide Cyclization.

The secondary structure plays a crucial role in the biological activity of peptides. Various strategies have been developed to stabilize particular peptide conformations, including sequence modifications and macrocyclization approaches. Often, the interplay between conformational constraint and flexibility is central to bioactivity. Here, we investigate how peptide α-helicity influences enzymatic head-to-tail cyclization using an engineered Sortase. We show that peptides with low helicity readily undergo intramolecular cyclization, while more rigid, helical peptides exhibit complex cyclization behaviors including cyclic dimer formation. These findings reveal that increased peptide rigidity can redirect enzymatic reactions from intramolecular to intermolecular processes, and demonstrates how changes in molecular rigidity can guide chemical reactivity. These insights can advance the design of peptide-derived materials, hydrogels, and stimuli-responsive probes.