Sequence-Dependent Assembly and Photoregulated Antibacterial Activity of Azobenzene-Modified Ultrashort Peptides

Ultrashort peptides are attractive supramolecular building blocks for constructing ordered nanostructures and bioactive materials. In this study, azobenzene-modified amphiphilic dipeptides and tripeptides were designed to investigate the cooperative effects of hydrophobic residues and photoresponsiveness on self-assembly behavior and antibacterial activity. Structural characterization revealed that tripeptides containing two aliphatic residues and one lysine residue (Azo-VVK and Azo-LLK) formed stable nanofibers with highly positive surface potentials in aqueous solution, whereas the dipeptides containing a single hydrophobic residue could not form ordered aggregates. Accordingly, the tripeptides displayed stronger antibacterial activity against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) (minimum inhibitory concentration, MIC ≤ 200 μM) than their dipeptide counterparts. Upon 365 nm irradiation, trans-to-cis photoisomerization of azobenzene disrupted the tripeptide assemblies and was accompanied by changes in their ζ-potentials and hydrophobic microenvironments, together with reduced antibacterial activity. Mechanistic studies suggested that the tripeptide assemblies killed bacteria through synergistic electrostatic and hydrophobic interactions, resulting in membrane disruption and bacterial death. In contrast, the antibacterial activities of the dipeptides showed little sensitivity to UV irradiation, although the azobenzene moieties remained photoisomerization features. This work provides insight into the development of light-responsive antibacterial ultrashort peptides through dynamic regulation of assembly structures, surface potentials, and the interfacial interactions between peptides and bacteria.