Photomodulation of actin filaments using spiropyran-modified peptide nanofibers

Abstract Modulating actin filament dynamics is crucial to understanding actin-mediated cellular processes and controlling cell functions artificially. This study developed a novel photoresponsive spiropyran (SP)/merocyanine (MC)-modified self-assembling peptide (SAP) linked with a LifeAct sequence (SAPSP/MC-LifeAct), which binds to filamentous actin at their C-terminus. Photoisomerization of the SP/MC unit enabled photocontrol of the peptide coassembly (SAPSP/MC-LifeAct + SAPSP/MC) process. Confocal laser scanning microscopy, stained with Thioflavin-T and transmission electron microscopy, revealed that the SP form self-assembled into nanofibers, whereas it dissociated in the MC form. In the SP form, the peptide coassembly could also successfully bind to actin filaments without significant morphological changes in the latter. However, upon UV irradiation of the actin filament/peptide nanofiber complex, SP was converted into MC, resulting in an irreversible change in the actin morphology from filament to an aggregated state. This light-responsive peptide assembly system provides a powerful platform for the spatiotemporal control of actin filament dynamics, with implications in cellular biophysics and bioengineering applications.