Low energy optical excitations as an indicator of structural changes initiated at the termini of amyloid proteins.

There is a growing body of experimental work showing that protein aggregates associated with amyloid fibrils feature intrinsic fluorescence. In order to understand the microscopic origin of this behavior observed in non-aromatic aggregates of peptides and proteins, we conducted a combined experimental and computational study on the optical properties of amyloid-derived oligopeptides in the near-UV region. We have focused on a few model systems having charged termini (zwitterionic) or acetylated termini. For the zwitterionic system, we were able to simulate the longer tail absorption in the near UV (250-350 nm), supporting the experimental results in terms of excitation spectra. We analyzed the optical excitations responsible for the low-energy absorption and found a large role played by charge-transfer states around the termini. These charge-transfer excitations are very sensitive to the conformation of the peptide and in realistic fibrils may involve inter and intra chain charge reorganization.

Lycopene, but not zeaxanthin, serves as a skeleton for the formation of an orthorhombic organization of intercellular lipids within the lamellae in the stratum corneum: Molecular dynamics simulations of the hydrated ceramide NS bilayer model.

Carotenoids play an important role in the protection of biomembranes against oxidative damage. Their function depends on the surroundings and the organization of the lipid membrane they are embedded in. Carotenoids are located parallel or perpendicular to the surface of the lipid bilayer. The influence of carotenoids on the organization of the lipid bilayer in the stratum corneum has not been thoroughly considered. Here, the orientation of the exemplary cutaneous carotenoids lycopene and zeaxanthin in a hydrated ceramide NS24 bilayer model and the influence of carotenoids on the lateral organization of the lipid bilayer model were studied by means of molecular dynamics simulations for 32 °C and 37 °C. The results confirm that lycopene is located parallel and zeaxanthin perpendicular to the surface of the lipid bilayer. The lycopene-loaded lipid bilayer appeared to have a strong orthorhombic organization, while zeaxanthin-loaded and pure lipid bilayers were organized in a disordered hexagonal-like and liquid-like state, respectively. The effect is stronger at 32 °C compared to 37 °C based on p-values. Therefore, it was assumed that carotenoids without hydroxyl polar groups in their structure facilitate the formation of the orthorhombic organization of lipids, which provides the skin barrier function. It was shown that the distance between carotenoid atoms matched the distance between atoms in the lipids, indicating that parallel located carotenoids without hydroxyl groups serve as a skeleton for lipid membranes inside the lamellae. The obtained results provide reasonable prediction of the overall qualitative properties of lipid model systems and show the importance of parallel-oriented carotenoids in the development and maintenance of the skin barrier function.