Theoretical Biophysics Group
Research Immobilized Artificial Membranes
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The unit cell used in molecular dynamics simulations of IAM.PC. The phosphatidylcholine (PC) molecules are shown in black, the 10-carbon hydrocarbon chains are shown in red and the water molecules are shown in light blue. The C10 molecules are interdigitated among PC molecules. The ends of the C10 and PC molecules are colvalently bonded to a silica substrate, located at the bottom of the cell and not shown.

An Immobilized Artificial Membrane (IAM) is a solid-phase membrane mimetic system, prepared by covalently binding membrane-forming lipids to an amorphous silica substrate. IAMs have been used successfully in the prediction of drug transport across cell membranes and in the purification and reconstitution of membrane proteins [1,2,3]. In order to understand and characterize IAMs on the molecular level, molecular dynamics simulations have been conducted on small patches of IAM surfaces. The typical size of the simulated IAM patches is 54 Å times 54 Å with approximately a 30 Å thick layer of waters solvating the surface. Two dimensional periodic boundary conditions are employed to increase the effective size of the simulations. However, this particular technique currently excludes the use of the Fast Multipole Method [4], so that simulations consisting of 10,000 - 15,000 atoms conducted on a single HP735 workstation achieve only about 5 ps per day.

Various molecular properties, such as functional group distributions and molecular order parameters, have been calculated from these simulations in order to characterize the similarities and differences between IAM surfaces and fluid bilayers. Preliminary results indicate to what extent the IAMs mimic the fluid bilayers and therefore suggest to what degree IAMs might be used to predict the drug-membrane interactions in fluid bilayers. Encouraged by these results, the TBG proposes to study drug-membrane interactions with IAM surfaces by means of computer simulation. The simplest system will require placing a small drug molecule at the interfacial region of an equilibrated IAM surface, using a sufficiently large patch of IAM surface. Additional waters will also be required to sufficiently solvate both the lipid head groups and the drug molecule.


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