Computational Studies of Texas Red-1,2-Dihexadecanoyl-sn-glycero-3-phosphoethanolamine-Model Building and Applications

Texas Red-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (TR-DHPE) is a frequently used experimental tool in the study of lipid membranes by fluorescence microscopy techniques. Although it is usually incorporated at low concentration, several experimental studies suggest that fluorescent labels could alter the membrane's behavior. To investigate this possibility, we developed and validated a molecular dynamics model for TR-DHPE. The model was used to simulate TR-DHPE in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers of 127 lipids and 511 lipids. We also simulated a pure 128 DPPC bilayer under the same conditions and found that the results compared well with other simulations and experiments. Texas Red was found to reside in the upper acyl chain region of the bilayer. Coinciding with its position in the bilayer, we found that Texas Red decreased the upper acyl carbon order parameters of neighboring lipids. We analyzed area per lipid at varying distances from the Texas Red and discovered finite size effects in the 1:127 system. In both systems, the Texas Red bound to a DPPC lipid. The model we have developed should also be useful for other biomolecular simulations which try to mimic experimental systems.