The ability of arginine-rich peptides to cross the lipid bilayer and enter cytoplasm, unlike their lysine-based analogues, is intensively studied in the context of cell-penetrating peptides. Although their penetration into the bilayer followed by the membrane thinning and fluidization remains rather vague from experimental point of view, the computational studies have shown that the type or charge of lipid polar groups is one of the crucial factors in their translocation. In the framework of this project, we propose to examine the impact of short cationic hydrophobic peptides adsorbed on lipid bilayer surface on lateral and transversal movement of constitutive lipids in inner and outer leaflets. By combining experimental and computational approaches, we aim at gaining an insight into the adsorption of peptides on lateral and longitudinal movement of lipids. In particular, symmetric and asymmetric lipid membranes will be examined with calorimetric, spectroscopic and microscopic techniques on the experimental side, and MD simulations and free-energy calculations on the computational side.

Myelin is multibilayered, dominantly lipid sheath that enwraps axons and ensures proper transmission of neural impulses. One of the most highlighted compositional attributes of myelin is the domination of lipids (70-85 %) over proteins of which the most significant are proteolipid protein (PLP) and myelin basic protein (MBP) (15-30 %), with representative lipids being phospholipids (phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), phosphatidylserines (PSs) and sphingomyelin (SM)) and cholesterol (chol). Disruption of spirally wrapped myelin sheath around axon axis is refferred as demyelination and it encompasses the effects such as the redundant unwrappping, vacuole formation and bilayer swelling due to water and ions leaking across the sheaths. Resulting with the impaired transmission of neural impulses, it produces clinical symptoms such as vision loss and muscle weakness which are common features of multiple sclerosis (MS). The studies of experimental autoimmune encephalomyelitis (EAE), as animal model of MS,  demonstrated that the amount and ratios of representative myelin lipids were significantly modified in contrast with myelin of normal varieties and are further accompanied by reduced adhesive activity of myelin basic protein (MBP). Although extensively explored in vitro and in vivo models, a more detailed picture of the molecular level events that drive the demyelination in all of its forms remains unknown. This project aims to tackle these unknows by examination of model myelin membranes of different sizes and composition (with respect to the normal and modified myelin) in the presence of MBP and its simpler subunits (peptides) that make a direct interaction with lipid membrane. Model myelin membranes will be prepared as large and giant uni- and multilamellar liposomes (LUVs/GUVs and MLVs/GMVs) and their response to the presence of peptides and MBP will be analyzed with microscopic and spectroscopic techniques, as well with the support provided by molecular dynamics simulations. Aside of understanding demyelination at the molecular level, obtained results will help in suggesting possible solutions in lipid composition regulation either by medications and appropriate nutrition or will provide the guidelines towards building-up the artificial myelin structure.

Mijelin je višestruko-dvoslojna, pretežno lipidna ovojnica koja omata aksone i osigurava pravilan prijenos živčanih impulsa. Gubitak cjelovitosti mijelina u obliku njegovog prekomjernog odmotavanja, stvaranja vakuola te bubrenja dvosloja naziva se demijelinizacijom koja je povezana s multiplom sklerozom (MS). In vivo studije provedene na oboljelim životinjama pokazale su da su količine najzastupljenijih lipida, uključujući fosfatidiletanolamine (PE), značajno promijenjene u usporedbi sa zdravima, a prati ih i smanjena adhezivna aktivnost mijelin-bazičnog proteina (MBP). Utjecaj povećanja PE u mješovitim modelnim lipidnim membranama na temperaturu faznog prijelaza iz lamelarne (La) u inverznu heksagonsku (HII) fazu, koji pokazuje strukturne sličnosti s formiranjem vakuola, značajan je, ali prilično nedokučiv problem. Cilj ovog prijedloga je naći vezu između spomenute temperaturne promjene te veličine i rasporeda PE-domena u mješovitim modelnim lipidnim membranama uz i bez prisustva MBP-a. Modelne mijelinske membrane priredit će se iz najzastupljenijih mijelinskih lipida u skladu s njihovim omjerima u normalnim i oboljelim jedinkama. Uz različito okruženje PE domena unutar dvosloja, zajedno s promjenama u hidratacijskom mediju u pogledu prisustva MBP-a te ionskog sadržaja, sustavno će se proučiti promjene temperature La do HII faznog prijelaza PE domena. Detaljna molekularna slika tih događaja dobit će se kombinacijom temperaturno-ovisne IR spektroskopije i računalne kemije; strukturne promjene PE domena tijekom ove fazne promjene otkrit će se zajedno s interakcijama između PE, MBP i susjednih domena. Odredit će se parametri koji se smatraju najkritičnijima u smanjenju temperature faznog prijelaza La do HII. Osim razumijevanja demijelinizacije na molekularnoj razini, dobiveni rezultati će također pomoći u predlaganju mogućih rješenja u regulaciji lipidnog sastava lijekovima te odgovarajućom prehranom.