Monte Carlo Simulations of Lipid Bilayers Containing Cholesterol
Author: Yvonne Nga Fong Yuan
Publisher:
Published: 2004
Total Pages: 0
ISBN-13:
DOWNLOAD EBOOKThe effects of cholesterol on the phase behaviour of lipid bilayers composed of Dilauroyl phosphatidylcholine (DLPC) and Dipalmitoyl phosphatidylcholine (DPPC) are investigated. Metropolis Monte Carlo simulations are performed on a 2-dimensional multi-state lattice model, which is a direct extension of the Pink model originally proposed to describe the main phase transition of single-component lipid bilayers. The binary mixture containing DLPC and DPPC was chosen because it is assumed to mimic lipid systems used in experimental investigations of the properties of rafts. Our calculations proceed as follows: (i) Simulations were first performed on single-component phosphatidylcholine (PC) bilayers with chain length ranging from 12 to 22. Our results were found to be in excellent agreement with previous simulations performed by different groups with the same parameter sets. (ii) Simulations on DLPC/cholesterol and DPPC/cholesterol bilayers were then performed, which were found to agree with experimental data from differential scanning calorimetry (DSC) and deuterium nuclear magnetic resonance (2H-NMR). A liquid-ordered (lo) phase which displays characteristics that are consistent with experimental observations is obtained from our model. Moreover, we found that formation of domains of different sizes can be induced by varying the interaction between the kink state and cholesterol in our model. (iii) Simulations on the binary DLPC/DPPC bilayers in the absence of cholesterol were next performed and reasonable agreement of our theoretical phase diagram with experimentally determined phase diagram from DSC and Fourier Transform Infrared (FTIR) experiments was found. (iv) Finally, simulations of DLPC/DPPC/cholesterol bilayers were performed, in conjunction with an exploration of the parameter space of the interaction between cholesterol and different lipid conformational states. We found that different parameter sets result in formation of domains of different size and component concentration. Two sets of parameters were chosen for which the system contains lo domains at physiological temperature, and at the same time exhibits a molecular order parameter profile that best resembles those from experimental FTIR data.