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Analyzing Heat Capacity Profiles of Peptide-Containing Membranes: Cluster Formation of Gramicidin A

V. P. Ivanova^*, I. M. Makarov^*, T. E. Schäffer and T. Heimburg^*

^* Membrane Biophysics and Thermodynamics Group, Department of Molecular Biology, Max-Planck-Institute for Biophysical Chemistry, 37070 Göttingen, Germany

Correspondence: Address reprint requests to T. Heimburg, E-mail: theimbu{at}gwdg.de; Web site: www.gwdg.de/theimbu.

The analysis of peptide and protein partitioning in lipid membranes is of high relevance for the understanding of biomembrane function. We used statistical thermodynamics analysis to demonstrate the effect of peptide mixing behavior on heat capacity profiles of lipid membranes with the aim to predict peptide aggregation from c_P-profiles. This analysis was applied to interpret calorimetric data on the interaction of the antibiotic peptide gramicidin A with lipid membranes. The shape of the heat capacity profiles was found to be consistent with peptide clustering in both gel and fluid phase. Applying atomic force microscopy, we found gramicidin A aggregates and established a close link between thermodynamics data and microscopic imaging. On the basis of these findings we described the effect of proteins on local fluctuations. It is shown that the elastic properties of the membrane are influenced in the peptide environment.

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