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Biomembranes are constantly remodeled and in cells, these processes are controlled and modulated by an assortment of membrane proteins. Here, it is shown that such remodeling can also be induced by photoresponsive molecules. The morphological control of giant vesicles in the presence of a water-soluble ortho-tetrafluoroazobenzene photoswitch (F-azo) is demonstrated and it is shown that the shape transformations are based on an increase in membrane area and generation of spontaneous curvature. The vesicles exhibit budding and the buds can be retracted by using light of a different wavelength. In the presence of F-azo, the membrane area can increase by more than 5% as assessed from vesicle electrodeformation. To elucidate the underlying molecular mechanism and the partitioning of F-azo in the membrane, molecular dynamics simulations are employed. Comparison with theoretically calculated shapes reveals that the budded shapes are governed by curvature elasticity, that the spontaneous curvature can be decomposed into a local and a nonlocal contribution, and that the local spontaneous curvature is about 1/(2.5 mu m). The results show that exo- and endocytotic events can be controlled by light and that these photoinduced processes provide an attractive method to change membrane area and morphology.
Cellular membranes constantly experience remodeling, as exemplified by morphological changes during endo- and exocytosis. Regulation of membrane morphology is essential for these processes. In this work, we attempt to establish a regulation path based on the use of photoswitches exhibiting conformational changes in model membranes, namely, giant unilamellar vesicles (GUVs). The mechanism of the changes in the GUVs’ morphology caused by isomerization of the photosensitive molecules has been previously explored but still remains elusive. We examine the morphological reshaping of GUVs in the presence of the photoswitch o-tetrafluoroazobenzene (F-azo) and show that the mechanism behind the resulting morphological changes involves both an increase in the membrane area and generation of a positive spontaneous curvature. First, we characterize the partitioning of F-azo in a single-component membrane using both experimental and computational approaches. The partition coefficient calculated from molecular dynamic simulations agrees with experimental data obtained with size-exclusion chromatography. Then, we implement the approach of vesicle electrodeformation in order to assess the increase in the membrane area, which is observed as a result of the conformational change of F-azo. Finally, the local and the effective membrane spontaneous curvatures were estimated from the observed shapes of vesicles exhibiting outward budding. We then extend the application of the F-azo to multicomponent lipid membranes, which exhibit a coexistence of domains in different liquid phases due to a miscibility gap between the lipids. We perform initial experiments to investigate whether F-azo can be employed to modulate the lateral lipid packing and organization. We observe either complete mixing of the domains or the appearing of disordered domains within the domains of more ordered phase. The type of behavior observed in response to the photoisomerization of F-azo was dependent on the used lipid composition. We believe that the findings introduced here will have an impact in understanding and controlling both lipid phase modulation and regulation of the membrane morphology in membrane systems.
Biomembranes are constantly remodeled and in cells, these processes are controlled and modulated by an assortment of membrane proteins. Here, it is shown that such remodeling can also be induced by photoresponsive molecules. The morphological control of giant vesicles in the presence of a water-soluble ortho-tetrafluoroazobenzene photoswitch (F-azo) is demonstrated and it is shown that the shape transformations are based on an increase in membrane area and generation of spontaneous curvature. The vesicles exhibit budding and the buds can be retracted by using light of a different wavelength. In the presence of F-azo, the membrane area can increase by more than 5% as assessed from vesicle electrodeformation. To elucidate the underlying molecular mechanism and the partitioning of F-azo in the membrane, molecular dynamics simulations are employed. Comparison with theoretically calculated shapes reveals that the budded shapes are governed by curvature elasticity, that the spontaneous curvature can be decomposed into a local and a nonlocal contribution, and that the local spontaneous curvature is about 1/(2.5 mu m). The results show that exo- and endocytotic events can be controlled by light and that these photoinduced processes provide an attractive method to change membrane area and morphology.