ACS PRF | ACS
All e-Annual Reports
43833-G4
Chemically Triggered Assembly of Peptide Materials
Stabilized helical peptides show potential as therapeutics capable of modulating protein function through enhanced helix-protein binding. Helix turn stabilization may be accomplished though covalent sidechain crosslinking on one face of the helix, in i and i+4 or i+7 positions,or replacement of a main chain hydrogen bond with a covalent linker.We report herein a new helix-nucleating i and i+4 crosslinking strategy based on copper catalyzed azide-alkyne [3+2] “click” cycloaddition and demonstrate the ability of this method and metal complexation to restore coiled-coil dimerization in a folding-incompetent sequence crippled by 2 helix-breaking glycine residues. This peptide structure stabilization strategy complements known intramolecular methods such as ring closing metathesis and allows convergent installation of functional groups pendant to the bis-alkyne linker that could be used to modulate peptide binding, targeting, and membrane permeability.
We studied 21 residue sequences derived from the GCN4 leucine zipper in which the central heptad contains glycine residues in the c and e helix positions and crosslinking residues (X) in the b and f (i and i+4) positions, leaving the hydrophobic core residues in the a and d positions intact as isoleucine and leucine, respectively (Figure 1). Metal complexation with i and i+4 X=His residues is known to induce monomeric helix folding, though it has not been previously demonstrated to restore structure in peptides containing 2 glycine residues. We postulated that the bis-triazole product of a double [3+2] cycloaddition between i and i+4 azidoalanine (Az) residues and a bis alkyne could yield a non-labile covalent linker isosteric with i and i+4 His-His metal complex (Figure 1A). We prepared peptides which may be crosslinked in the central heptad by Ni2+ complexation with histidine and bis-alkyne cyclization with Az, respectively. Indeed, side chain crosslinking by these methods restores both folding and dimerization. We have thus demonstrated a new methodology for helix structural nucleation using double azide-alkyne [3+2] cycloadditions to form i and i+4 constrained peptide sequences. This chemistry is sufficiently robust to allow intermolecular cyclization with few sideproducts, setting the stage for convergent functionalization and structure nucleation. This technology may be useful as a means of synthesizing new building blocks for peptide-based materials or preparing stabilized helical peptides capable of binding protein interfaces and altering biological function. These studies are currently underway in our lab. The acceptance of this study for publication, which cites PRF support, is pending.
