Top (left) and cross-sectional (right)
views of snapshots of final simulation structures of NeuTM35 peptide
in mixed DMPC-DDPC bilayers. Average DMPC composition
is 55.8%. Green, blue, and red represent
peptide, DMPC, and DDPC respectively. Phosphorus atoms are shown as
spheres in the right-hand panels. Water is omitted for clarity
Transmembrane peptides, or protein segments, typically consist of a hydrophobic region flanked by hydrophilic regions. Providing an appropriate environment for all regions of a TM peptide can involve local distortions of the bilayer thickness to resolve any "hydrophobic mismatch" between the length of the hydrophobic segment and the thickness of the bilayer's hydrophobic interior. In a mixed bilayer, these distortions may attract or repel lipids with different properties, producing local deviations in composition. Experimental investigations over many years using a range of experimental approaches have come to different conclusions about the degree of such sorting effects. Our MCMD Simulations of the transmembrane helix gramicidin A in DSPC/DMPC and DMPC/DDPC mixtures showed only a very weak sorting, with a local enrichment of the more favorable lipid of under 5%.(Yin & Kindt, 2010). Further simulations in progress on a larger beta-barrel peptide, OmpA, have yielded moderately stronger sorting effects.(Yin & Kindt, 2011, submitted to Biophysical Journal).