This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.Highly aligned stacks of lipid membranes can be prepared by self assembly on flat smooth surfaces forming a smectic-C liquid crystal structure with water intercalated between the bilayers formed by the lipid molecules. Such samples of aligned membranes have been extensively used for diffraction experiments concentrating on the structure of the membrane along the bilayer normal. In studying lipid-protein interactions it is also highly informative to look at the lateral distribution of the proteins in the membrane plane. We started a series of experiments on aligned phospholipid membranes of different thickness containing the dimeric ion channel Gramicidin. Using the newly developed sample chamber with humidity and temperature control, we investigated the change in the nearest neighbor distance between the peptides inside the membrane as a function of thickness and hydration state of the membrane. We find that the average peptide-to-peptide distance increases with increasing thickness of the bilayer. This effect is attributed to the increased repulsive interaction of the peptides due to the hydrophobic mismatch between the peptide and the lipid. In addition to the membrane mediated interaction between the peptides within the same membrane plane, we found that below a relative air humidity of 85% the peptide in neighboring membranes start to interact with each other leading to a partial ordering of of the peptides across the membrane stack.
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