Dimyristoylphosphatidylcholine Lipid Bilayer Research Articles

Molecular dynamics simulations of an antifreeze protein at the lipid / water interface

The ability of antifreeze proteins (AFP's) and glycoproteins (AFGP's) to prevent damage to certain organisms under cold stress is well established. These molecules have also been shown to prevent chilling damage in some biological membranes and interaction between membranes and AF(G)P's has been observed during chilling events; however, the exact mechanism of membrane stabilization is still not well understood. Molecular modelling is an ideal technique for probing atomistic information in these systems although modelling studies to date have focused on peptide structure and the site and mode, e.g., insertion, of the peptide-membrane interaction. To provide insight into how AF(G)P's may act to stabilize (or destabilize) membranes during phase transitions, we have conducted molecular dynamics (MD) simulations of a solvated dimyristoylphosphatidylcholine (DMPC) lipid bilayer containing an AFP Type I at the lipid/water interface at several temperatures. We present the analysis of several properties of the phospholipid bilayer that are relevant when considering phase transitions. Possible areas for concentrating future research efforts have been highlighted; namely the acyl chain order and the polar headgroups, both of which have been implicated in experimental studies of the stabilization of model membranes by AF(G)P's.

Surprising Rigidity of Functionally Important Water Molecules Buried in the Lipid Headgroup Region.

Understanding water dynamics and structure is an important topic in biological systems. It is generally held in the literature that the interfacial water of hydrated phospholipids is highly mobile, in fast exchange with the bulk water ranging from the nano- to femtosecond timescale. Although nuclear magnetic resonance (NMR) is a powerful tool for structural and dynamic studies, direct probing of interfacial water in hydrated phospholipids is formidably challenging due to the extreme population difference between bulk and interfacial water. We developed a novel 17O solid-state NMR technique in combination with an ultra-high-field magnet (35.2 T) to directly probe the functionally important interfacial water. By selectively suppressing the dominant bulk water signal, we observed two distinct water species in the headgroup region of hydrated dimyristoylphosphatidylcholine (DMPC) lipid bilayers for the first time. One water species denoted as "confined water" is chemically and dynamically different from the bulk water (∼0.17 ppm downfield and a slightly shorter spin-lattice relaxation time). Another water species denoted as "bound water" has severely restricted motion and a distinct chemical shift (∼12 ppm upfield). Additionally, the bulk water is not as "free" as pure water, resulting from the fast exchange with the water molecules that weakly and transiently interact with the lipid choline groups. These new discoveries clearly indicate the existence of the interfacial water molecules that are relatively stable over the NMR timescale (on the order of milliseconds), providing an opportunity to characterize water dynamics on the millisecond or slower timescale in biomacromolecules.

Structural changes of interfacial water upon fluid-ripple-gel phase transitions of bilayers

All atom molecular dynamics simulations of fully hydrated dimyristoylphosphatidylcholine lipid bilayers are performed for total 9.45 μs showing a fluid to a ripple to a gel phase transition. Changes in the radial distribution functions and angular distribution functions of the interface water (IW) signify a shift from a distorted tetrahedral to a tetrahedral arrangement upon decrease in temperature at the gel phase. The potential of mean forces of the IW follow two cross-overs near both phase transitions unlike the BW. Our analyses reveal a strong correlation between bilayer phase transitions and the structural properties of the IW.

Met35 Oxidation Hinders Aβ25-35 Peptide Aggregation within the Dimyristoylphosphatidylcholine Bilayer.

Using all-atom explicit solvent replica exchange molecular dynamics simulations, we studied the aggregation of oxidized (ox) Aβ25-35 peptides into dimers mediated by the zwitterionic dimyristoylphosphatidylcholine (DMPC) lipid bilayer. By comparing oxAβ25-35 aggregation with that observed for reduced and phosphorylated Aβ25-35 peptides, we elucidated plausible impact of post-translational modifications on cytotoxicity of Aβ peptides involved in Alzheimer's disease. We found that Met35 oxidation reduces helical propensity in oxAβ25-35 peptides bound to the lipid bilayer and enhances backbone fluctuations. These factors destabilize the wild-type head-to-tail dimer interface and lower the aggregation propensity. Met35 oxidation diversifies aggregation pathways by adding monomeric species to the bound conformational ensemble. The oxAβ25-35 dimer becomes partially expelled from the DMPC bilayer and as a result inflicts limited disruption to the bilayer structure compared to wild-type Aβ25-35. Interestingly, the effect of Ser26 phosphorylation is largely opposite, as it preserves the wild-type head-to-tail aggregation interface and strengthens, not weakens, aggregation propensity. The differing effects can be attributed to the sequence locations of these post-translational modifications, since in contrast to Ser26 phosphorylation, Met35 oxidation directly affects the wild-type C-terminal aggregation interface. A comparison with experimental data is provided.

Observation of Translational Diffusion in a Planer Supported Lipid Bilayer Membrane by Total Internal Reflection-Transient Grating Method

Abstract Total internal reflection-transient grating (TIR-TG) method has been applied to diffusion coefficient measurements of trans-stilbene in a dimyristoylphosphatidylcholine (DMPC) lipid bilayer membrane at a silica/water interface. The observed TIR-TG signal consisted of four decay components. The rate constants of the third and fourth components quadratically depended on grating wavenumbers, which indicates that these components represent diffusion processes of trans-stilbene (diffusion signals). From the decay rate constants of the diffusion signals, two different diffusion coefficients, (5.7 ± 1.0) × 10−10 and (2.8 ± 0.5) × 10−12 m2s−1 were obtained for trans-stilbene in the DMPC membrane. This result indicates that the DMPC membrane is an inhomogeneous environment that can be described with two different effective viscosities.

31P and 13C solid-state NMR analysis of morphological changes of phospholipid bilayers containing glucagon during fibril formation of glucagon under neutral condition

Glucagon is a 29 amino acid peptide hormone secreted by pancreatic α-cells that interacts with specific receptors located in various organs. Glucagon tends to form gel-like fibrillar aggregates that are cytotoxic due to their activation of apoptotic signaling pathways. To understand the glucagon-membrane interactions, morphological changes in dimyristoylphosphatidylcholine (DMPC) bilayers containing glucagon in neutral solution were investigated by observing 31P NMR spectra. First, lipid bilayers with a DMPC/glucagon molar ratio of 50/1 were observed. One day after preparing the DMPC/glucagon lipid bilayer sample, lipid bilayers were disrupted below the phase transition temperature (Tc). Membrane disruption was reduced 2 days after preparation due to the reduction of glucagon-DMPC interaction, and subsequently increased by 4 days and was reduced again by 7 days. TEM measurements showed that small ellipsoidal intermediates of glucagon were observed inside the small size of lipid bilayer after 4 days, while fibrils grew inside lipid bilayer after 19 days. These results indicate that morphological changes in DMPC/glucagon lipid bilayers are correlated with the evolution of glucagon aggregate state. Particularly, fibril intermediate shows a strong glucagon lipid bilayer interaction. We further investigated the structure and kinetics of glucagon fibril formation inside the DMPC lipid bilayer in a neutral solution using 13C solid-state NMR spectroscopy. α-Helical structures were observed around Gly4 and Ala19 in the monomeric form, which changed to β-sheet structures in the fibril form. The fibrillation process can be explained by a two-step autocatalytic reaction mechanism in which the first step is a homogeneous nuclear formation (k1), and the second step is an autocatalytic heterogeneous fibrillation process (k2).

Effect of Cholesterol and 6-Ketocholestanol on Membrane Dipole Potential and Sterol Flip-Flop Motion in Bilayer Membranes.

A variety of experimental and theoretical approaches have been employed to investigate the sterol flip-flop motion in lipid bilayer membranes. However, the sterol effect on the dipole potential of lipid bilayer membranes is less well studied and the influence of dipole potential on sterol flip-flop motion in lipid bilayer membranes is less well understood. In our previous works, we have demonstrated the performance of our coarse-grained (CG) model in the computation of the dipole potential. In this work, five 30 μs CG simulations of dimyristoylphosphatidylcholine (DMPC) bilayers were carried out at different sterol concentrations (in a range from 10 to 50% mole fraction). Then, a comparison was made between the effects of cholesterol (CHOL) and 6-ketocholestanol (6-KC) on the dipole potential of DMPC lipid bilayers as well as the sterol flip-flop motion. Our CG simulations show that the membrane dipole potential is impacted more significantly by 6-KC than by CHOL. This finding is consistent with recent experimental studies. Meanwhile, our work suggests that the sterol-sterol interactions (in particular, electrostatic interactions) should be critical to the formation of sterol-sterol clusters, which would hinder the sterol flip-flop motion inside the lipid bilayers. This is in support of the recent experimental study on the sterol transportation in lipid bilayer membranes.

Binding of Cytotoxic Aβ25-35 Peptide to the Dimyristoylphosphatidylcholine Lipid Bilayer.

Aβ25-35 is a short, cytotoxic, and naturally occurring fragment of the Alzheimer's Aβ peptide. To map the molecular mechanism of Aβ25-35 binding to the zwitterionic dimyristoylphosphatidylcholine (DMPC) bilayer, we have performed replica exchange with solute tempering molecular dynamics simulations using all-atom explicit membrane and water models. Consequences of sequence truncation on the binding mechanism have been measured by utilizing as a control our previous simulations probing binding of the longer peptide Aβ10-40 to the same bilayer. The most intriguing feature of Aβ25-35 binding to the DMPC bilayer is a coexistence of two bound states with strikingly different characteristics: a dominant surface-bound state and a less stable inserted state. In the surface-bound state, the peptide samples extended conformations, in which its unbound C-terminal is pointed away from the bilayer. In contrast, in the inserted state, the C-terminal resides deep in the bilayer hydrophobic core. In both states, the N-terminal remains anchored to the bilayer. Free energy landscape analysis reveals that the two states are separated by a moderate barrier, suggesting that Aβ25-35 monomer may frequently interconvert between them. The net effect of Aβ25-35 binding is a minor impact on the bilayer structure, which contrasts with the considerable bilayer perturbations induced by a longer Aβ10-40 peptide penetrating deep into the bilayer core. Therefore, we conclude that the binding mechanisms of Aβ25-35 and Aβ10-40 peptides are different. Potential implications of our results for Aβ25-35 cytotoxicity are discussed. A comparison of experimental data with our findings reveals a good agreement.

Interaction of a chloride channel blocker with a lipid bilayer membrane and subsequent effect of addition of submicellar concentrations of bile salt

The present study demonstrates the interaction of potential chloride channel blocker drug, namely, 9-methylanthroate (9MA) with dimyristoylphosphatidylcholine (DMPC) lipid bilayer membrane in the solid gel (SG, at 15 °C) and liquid crystalline (LC, at 37 °C) phases of the lipid. Our spectroscopic results reveal a relatively greater degree of partitioning of the drug molecules into the DMPC lipid membrane at 37 °C (LC phase) compared to that at 15 °C (SG phase). Furthermore, the study is extended to explore the interaction of a bile salt (sodium deoxycholate, NaDC) with the DMPC lipid bilayer membrane in the SG as well as LC phase utilizing the environment-sensitive photophysical characteristics of the drug. Our steady-state and time-resolved spectroscopic results are invoked to critically analyze all the possibilities of bile salt-induced modulation of the photophysical behavior of the lipid-bound drug e.g., (i) expulsion of the lipid-bound drug molecules to the bulk aqueous phase upon addition of the bile salt, (ii) redistribution of population of the drug molecules within the lipid membrane and (iii) penetration of water molecules into the lipid bilayer membrane and thereby altering the hydration structure of the membrane. Cumulatively, our results appear to converge on the possibility of bile salt-induced hydration of the interfacial region of the lipid membrane as the actuating mechanism of the lipid-bile salt interaction. It is imperative to state that the present study emphasizes on the interaction of DMPC lipid membrane with the bile salt (NaDC) only in the submicellar concentration regime of NaDC which involves no significant perturbation of the lipid vesicle structure.

Effects of Channel Forming Peptides on Lipid Bilayer Dynamics and Leaflet Coupling

Altering the material properties of lipid bilayers has been shown to affect the biological activity of a number of channel-forming peptides and proteins. A prototypical example is gramicidin, in which the channel formation and lifetime directly depends on the lipid membrane in which it is embedded. However, less is known about how a membrane-spanning channel affects the lipid bilayer properties, particularly the elasticity. Here we use neutron spin echo spectroscopy (NSE) to measure both the collective bending and thickness fluctuation dynamics in dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) bilayers containing gramicidin at low peptide/lipid ratios. At these low concentrations, gramicidin incorporation did not have a measurable effect on the average bilayer structure but significantly impacted the collective membrane dynamics. The bending modulus of DMPC membranes increased with increasing gramicidin concentration, while the trend in DPPC was non-monotonic and first decreased at low gramicidin concentrations before increasing at higher concentrations. In contrast, the thickness fluctuation amplitude increased with increasing gramicidin concentration in both the DMPC and DPPC lipid bilayers. Notably, combining the bending and thickness fluctuation results revealed that the seemingly disparate concentration trends in the DMPC and DPPC lipid bilayers were both consistent with an increase in coupling between the bilayer leaflets with increasing gramicidin concentration. Together these results demonstrate that channel formation can have considerable effects on the surrounding lipid membrane elasticity and highlight the interplay between lipids and peptides in determining the membrane dynamics.

Combination of anti-hypertensive drugs: a molecular dynamics simulation study

The anti-hypertensive drugs amlodipine, atenolol and lisinopril, in ordinary and PEGylated forms, with different combined-ratios, were studied by molecular dynamics simulations using GROMACS software. Twenty simulation systems were designed to evaluate the interactions of drug mixtures with a dimyristoylphosphatidylcholine (DMPC) lipid bilayer membrane, in the presence of water molecules. In the course of simulations, various properties of the systems were investigated, including drug location, diffusion and mass distribution in the membrane; drug orientation; the lipid chain disorder as a result of drug penetration into the DMPC membrane; the number of hydrogen bonds; and drug surface area. According to the results obtained, combined drugs penetrate deeper into the DMPC lipid bilayer membrane, and the lipid chains remain ordered. Also, the combined PEGylated drugs, at a combination ratio of 1:1:1, enhance drug penetration into the DMPC membrane, reduce drug agglomeration, orient the drug in a proper angle for easy penetration into the membrane, and decrease undesirable lipotoxicity due to distorted membrane self-assembly and thickness. Graphical abstract ᅟ.

Does Replica Exchange with Solute Tempering Efficiently Sample Aβ Peptide Conformational Ensembles?

We have applied replica exchange with solute tempering (REST) molecular dynamics to study a short fragment of the Aβ peptide, Aβ25-35, in water and a much larger system incorporating two Aβ10-40 peptides binding to the zwitterionic dimyristoylphosphatidylcholine (DMPC) bilayer. As a control, we used traditional replica exchange molecular dynamics (REMD) applied to the same systems. Our objective was to assess the practical utility of REST simulations. Taken together, our results suggest four conclusions. First, compared to REMD, the number of replicas in REST simulations can be reduced four to five times without affecting the temperature range or compromising an efficient random walk of REST replicas over temperatures. Second, although overall REST produces much fewer conformational states than REMD, there is no substantial difference in the collection of unique states for the wild-type replica in REST and REMD, especially for the system featuring Aβ peptides binding to the lipid bilayer. Third, we performed a thorough comparison of REST and REMD equilibrium conformational ensembles, including thermal averages and probability distributions. REST reproduces REMD data extremely well for the system of Aβ peptides binding to the DMPC lipid bilayer. The agreement between REST and REMD equilibrium sampling of Aβ25-35 in water is less perfect, but it improves with addition of new REST simulations. Surprisingly, REST demonstrates much better convergence for the system featuring ordered peptides binding to lipid bilayer rather than for a small unstructured peptide solvated in water. Fourth, REST delivers its full computational advantage over REMD when applied to peptides interacting with lipid bilayers. For peptides solvated in water, REST does not appear to offer computational gain but may make replica simulations practically feasible due to a lower requirement for parallel computing environments. Our study is expected to facilitate wider application of REST in biomolecular simulations.

Study of procaine and tetracaine in the lipid bilayer using molecular dynamics simulation.

Despite available experimental results, the molecular mechanism of action of local anesthetics upon the nervous system and contribution of the cell membrane to the process are still controversial. In this work, molecular dynamics simulations were performed to investigate the effect of two clinically used local anesthetics, procaine and tetracaine, on the structure and dynamics of a fully hydrated dimyristoylphosphatidylcholine lipid bilayer. We focused on comparing the main effects of uncharged and charged drugs on various properties of the lipid membrane: mass density distribution, diffusion coefficient, order parameter, radial distribution function, hydrogen bonding, electrostatic potential, headgroup angle, and water dipole orientation. To compare the diffusive nature of anesthetic through the lipid membrane quantitatively, we investigated the hexadecane/water partition coefficient using expanded ensemble simulation. We predicted the permeability coefficient of anesthetics in the following order: uncharged tetracaine>uncharged procaine>charged tetracaine>charged procaine. We also shown that the charged forms of drugs are more potent in hydrogen bonding, disturbing the lipid headgroups, changing the orientation of water dipoles, and increasing the headgroup electrostatic potential more than uncharged drugs, while the uncharged drugs make the lipid diffusion faster and increase the tail order parameter. The results of these simulation studies suggest that the different forms of anesthetics induce different structural modifications in the lipid bilayer, which provides new insights into their molecular mechanism.

Effect of curcumin on lateral diffusion in lipid bilayers

Lateral diffusion in dimyristoylphosphatidylcholine lipid bilayers decreases in the presence of cholesterol and curcumin, as measured by 1 H NMR spectroscopy, but the mechanisms of action of these two compounds are different.

Structural and functional effects of benzimidazole/thioether–copper complexes with antitumor activity on cell membranes and molecular models

Two cytotoxic copper(II) complexes with N–H and N-methylated benzimidazole-derived ligands (Cu-L2 and Cu-L2Me) were synthesized and made to interact with human erythrocytes and molecular models of their plasmatic membranes. The latter consisted in lipid bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), lipids of the types present in the outer and inner monolayers of the human erythrocyte membrane, respectively. Initial assessment of the interaction of the complexes with DMPC and DMPE consisted of X-ray diffraction studies, which showed preferential interactions with the former. Scanning electron microscopy (SEM) of erythrocytes incubated with solutions of the Cu(II) complexes evidenced deformation of the cells to stomatocytes and knizocytes by Cu-L2 and Cu-L2Me due to interactions with the inner and outer leaflets of the cell membranes, respectively. This was further confirmed by real-time observation of the dose-dependent effects of the complexes on live erythrocytes by defocusing microscopy (DM). The combined observations, including the increased antiproliferative activity of the N-methylated complex Cu-L2Me over that of Cu-L2 is rationalized based on the higher lipophilicity of the former. This property would facilitate passive diffusion of Cu-L2Me through the cell membrane, particularly in the initial stages when the DMPC-rich outer leaflet is involved. In contrast, the benzimidazole N–H groups of Cu-L2 may participate in hydrogen bonding with DMPE polar groups; this result is consistent with the formation of stomatocyte induced by the latter complex.

Location, Partitioning Behavior, and Interaction of Capsaicin with Lipid Bilayer Membrane: Study Using Its Intrinsic Fluorescence.

Capsaicin is an ingredient of a wide variety of red peppers, and it has various pharmacological and biological applications. The present study explores the interaction of capsaicin with dimyristoylphosphatidylcholine (DMPC) lipid bilayer membrane by monitoring various photophysical parameters using its intrinsic fluorescence. In order to have a clearer understanding of the photophysical responses of capsaicin, studies involving (i) its solvation behavior in different solvents, (ii) the partition coefficient of capsaicin in different thermotropic phase states of lipid bilayer membrane, and (iii) its location inside lipid bilayer membrane have been carried out. Capsaicin has a reasonably high partition coefficient for DMPC liposome membrane, in both solid gel (2.8 ± 0.1 × 10(5)) and liquid crystalline (2.6 ± 0.1 × 10(5)) phases. Fluorescence quenching study using cetylpyridinium chloride (CPC) as quencher suggests that the phenolic group of capsaicin molecule is generally present near the headgroup region and hydrophobic tail present inside hydrophobic core region of the lipid bilayer membrane. The intrinsic fluorescence intensity and lifetime of capsaicin sensitively respond to the temperature dependent phase changes of liposome membrane. Above 15 mol %, capsaicin in the aqueous liposome suspension medium lowers the thermotropic phase transition temperature by about 3 °C, and above 30 mol %, the integrity of the membrane is significantly lost.

Calcium Enhances Binding of Aβ Monomer to DMPC Lipid Bilayer

Using isobaric-isothermal replica-exchange molecular dynamics and the all-atom explicit-solvent model, we studied the equilibrium binding of Aβ monomers to a zwitterionic dimyristoylphosphatidylcholine (DMPC) bilayer coincubated with calcium ions. Using our previous replica-exchange molecular dynamics calcium-free simulations as a control, we reached three conclusions. First, calcium ions change the tertiary structure of the bound Aβ monomer by destabilizing several long-range intrapeptide interactions, particularly the salt bridge Asp23-Lys28. Second, calcium strengthens Aβ peptide binding to the DMPC bilayer by enhancing electrostatic interactions between charged amino acids and lipid polar headgroups. As a result, Aβ monomer penetrates deeper into the bilayer, making disorder in proximal lipids and bilayer thinning more pronounced. Third, because calcium ions demonstrate strong affinity to negatively charged amino acids, a considerable influx of calcium into the area proximal to the bound Aβ monomer is observed. Consequently, the localizations of negatively charged amino acids and calcium ions in the Aβ binding footprint overlap. Based on our data, we propose a mechanism by which calcium ions strengthen Aβ-bilayer interactions. This mechanism involves two factors: 1) calcium ions make the DMPC bilayer partially cationic and thus attractive to the anionic Aβ peptide; and 2) destabilization of the Asp23-Lys28 salt bridge makes Lys28 available for interactions with the bilayer. Finally, we conclude that a single Aβ monomer does not promote permeation of calcium ions through the zwitterionic bilayer.

A study of HIV-1 FP inhibition by GBV-C peptides using lipid nano-assemblies

Abstract Langmuir–Blodgett films (LBs) and supported lipid bilayers (SLBs) of dimyristoylphosphatidylcholine (DMPC)–dimyristoylphosphatidylserine (DMPS) (3:2) were used to investigate the way that a GBV-C peptide (P45) inhibits the immunodeficiency human virus fusion peptide (HIV-1 FP) action at membrane level. Supported lipid bilayers (SLBs) were prepared by direct adsorption of a liposomal dispersion on solid mica slides and Langmuir–Blodgett films (LBs) by a deposition of a monolayer onto mica solid surface at different compression pressures. The behaviour of P45, HIV-1 FP and a mixture of P45 and HIV-1 FP (1:1) were monitored in the two phospholipid membrane models by fluorescence microscopy (FM) and atomic force microscopy (AFM). Experiments with SLBs confirmed that P45 inhibited HIV-1 FP action in vitro. LBs obtained at 10 and 25 mN m−1 confirmed different lipid interactions for DMPC/DMPS (3:2) in combination with either P45 (8:2), HIV-1 FP (8:2), or P45 and HIV-1 FP (8:1:1). The P45 peptide was confirmed to modulate the action of HIV-1 FP. Furthermore, FM and AFM images showed that HIV-1 FP had a pressure-independent membrane-level behaviour when compared with P45 and the P45 + HIV-1 FP (1:1) mixture. This mixture also had dramatic effects on the appearance of liquid expanded (LE)–liquid condensed (LC) phase coexistence as shown by FM and AFM.

Molecular dynamics study of changes in physico-chemical properties of DMPC lipid bilayers by addition of nonionic surfactant C12E10

Changes in physico-chemical properties of dimyristoyl phosphatidylcholine (DMPC) lipid bilayers caused by the addition of 9.4 mol% nonionic surfactant decaoxyethylene monododecyl ethers (C12E10) have been investigated by molecular dynamics calculations. In spite of addition of single chain C12E10, the lipid bilayers showed an increase of membrane area. Isothermal area compressibility, which is a measure of membrane softness in lateral direction, also increased by 50% for DMPC/C12E10 mixed bilayers. Furthermore, the order parameter of C–H vector for DMPC acyl tails decreased. We found that these changes are caused by the hydrophilic head groups of C12E10 which are located near the glycerol backbone of the DMPC molecules and have bulky random coil conformation without any preferential ordered structures.

Molecular dynamics simulations and free energy profile of Paracetamol in DPPC and DMPC lipid bilayers

Molecular dynamics (MD) simulations and biased MD simulation were carried out for the neutral form of Paracetamol inserted in fully hydrated dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) lipid bilayers. For comparison, fully hydrated DMPC and DPPC lipid bilayers were also simulated separately without Paracetamol. The simulation time for each system was 50 ns. At two concentrations of Paracetamol, various properties of the lipid bilayer such as area per lipid, order parameter, diffusion coefficient, radial distribution function, electrostatic potential, mass density and hydrogen bonds have been calculated. Also, the convergence in time of the free energy profile of the Paracetamol along a DPPC bilayer normal was calculated by umbrella sampling method. From the obtained results, it can be concluded that neutral form of Paracetamol shows a generally similar behaviour in DPPC and DMPC lipid bilayers. It was shown that the addition of Paracetamol causes a decrease in tail order parameter of both DPPC and DMPC lipid bilayers and the tail of Paracetamol adopts an inward orientation in the lipid bilayers. Also from the free energy profile, the high penetration barrier in the bilayer centre was determined. The behaviour of Paracetamol in different dosages in two types of lipid bilayer membranes, DPPC and DMPC has been investigated by MD simulation. For the neutral form of the drug, the best position in the membrane has been identified by free energy calculations.