Templated assembly of the pH-sensitive membrane-lytic peptide GALA

Delivery of protein or nucleic acid therapeutics into intracellular compartments may require facilitation to allow these macromolecules to cross otherwise impermeant cellular membranes. Peptides capable of forming membrane-spanning channels hold promise as just such facilitators, although the requirement for peptide oligomerization to form these channels may limit their effectiveness. Synthetic molecules containing multiple copies of membrane-active peptides attached to a template molecule in a pre-oligomerized form have attracted interest for drug-delivery applications. Using three template designs, we synthesized multimeric versions of the pH-sensitive lytic peptide GALA and compared their performance to monomeric GALA. Template assembly stabilized helix formation: templated GALA retained alpha-helical structure even at neutral pH, unlike monomeric GALA. In membrane leakage assays, templated GALA retained the pH sensitivity of the monomer, with improved leakage for dimeric GALA. Surprisingly, trimeric GALA was less effective, particularly when synthesized with a larger and more flexible spacer. Surface plasmon resonance analysis indicated that reversible binding of templated GALA to lipid surfaces at acidic conditions was greatly reduced compared with monomeric GALA, but that the amount of irreversibly bound material was similar. We interpreted these results to indicate that templated peptides may cyclize into 'self-satisfied' oligomeric structures, incapable of further aggregation and subsequent pore formation. Future design of templated peptides must be carefully performed to avoid this unwanted consequence.