Charge and length dependent build-up of environment sensitive lamellin β-peptides†

Supramolecular constructs of peptides with their unique morphologies and biomimetic nature exhibit immense potential in developing functional biomaterials. β-Peptides are imperative in this respect due to their propensity to form proteolytically stable, diverse and structurally well-defined assemblies. Our recent investigations focused on the assembly patterns of neutral heterochiral acyclic β³-peptide sequences which showed enhanced antibacterial activity upon introduction of positively charged side chains. These sequences adopt a lamellar morphology in phosphate rich media, hence are termed lamellins. Notably, slight sequential modifications also resulted in changes in assembly formation. Thus, to better understand their properties, four peptides have been synthesized with gradually increasing cationic nature and length varied between hexa- and octapeptides, while preserving the hydrophobic N-terminal and the alternating chirality along the backbone. The effect of charge and length on the morphology and supramolecular organization of these sequences in high-salt phosphate conditions (PBS) and low ionic strength water were systematically investigated. With an increase in charge, the affinity for assembly formation increased in PBS and decreased in water. The octapeptides exhibited a higher affinity for ordered assembly formation when compared to the hexapeptides as demonstrated in their unique CD spectral pattern, suggesting altered chirality at the supramolecular level. In the presence of liposomes, a more homogenous conformational distribution was observed in PBS media, with the large assemblies of the octapeptides retaining their molecular conformation. Hemolysis assays demonstrated that minor sequence modifications could result in an order of magnitude difference in activity. Thus, through selective modifications of the peptide backbone, novel supramolecules can be engineered with tailored morphology, physicochemical and membrane characteristics, which can be used for targeted biological applications.