Search

Cyclic peptides that modulate protein-protein interactions can be valuable therapeutic candidates if they can be delivered intact to their target proteins in cells. Here we systematically compare the effects of different helix-inducing cyclization constraints on the capacity of a macrocyclic peptide component to confer α-helicity, protein-binding affinity, resistance to degradative proteases and cell uptake to a 12-residue peptide fragment of tumor suppressor protein p53. We varied the helix-inducing constraint (hydrocarbon, lactam, aliphatic or aromatic thioether, etc. ) and the position of the cyclization linker ( i to i + 4 or i to i + 7 bridges) in order to sculpt the macrocyclic size, stabilize its structure, and promote cell uptake. We find that rigidifying the macrocycle leads to higher alpha helicity, target affinity and proteolytic stability to different extents, whereas cell uptake of compounds shown here is mostly driven by hydrophobicity and aromaticity of the macrocycle., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

Most protein-protein interactions occur inside cells. Peptides can inhibit protein-protein interactions but tend not to enter cells. We systematically compare cell permeability for 8-12 residue model peptides with helix-inducing lactam/hydrocarbon linkers between amino acid sidechains. Cell uptake increases when hydrophobic residues and lactam linkers (i, i + 4) form a contiguous hydrophobic surface patch. Uptake increases further when both hydrophobic and positively charged (but not neutral or negative) residues are clustered into like surface patches. Amphipathicity alone is however insufficient for cell uptake of acyclic sequences. Changing the linker from lactam to hydrocarbon further increases uptake, but also promotes cell lysis. Helicity, positive charge and amphipathicity together promote cell permeability. Most known bioactive helical peptides do not optimally cluster residues for amphipathicity and so are likely unoptimised for cell uptake.