Thermodynamics of Melittin Binding to Lipid Bilayers : aggregation/Pore Formation

Klocek, G. and Schulthess, T. and Shai, Y. and Seelig, J.. (2009) Thermodynamics of Melittin Binding to Lipid Bilayers : aggregation/Pore Formation. Biochemistry, Vol. 48, H. 12. pp. 2586-2596.

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Official URL: http://edoc.unibas.ch/dok/A5257371

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Lipid membranes act as catalysts for protein folding. Both alpha-helical and beta-sheet structures can be induced by the interaction of peptides or proteins with lipid surfaces. Melittin, the main component of bee venom is a particularly well-studied example for the membrane-induced random coil-to-?-helix transition. Melittin in water adopts essentially a random coil conformation. The cationic amphipathic molecule has a high affinity for neutral and anionic lipid membranes and exhibits about 50-65% ?-helix conformation in the membrane-bound state. At higher melittin concentrations, the peptide forms aggregates/pores in the membrane. In spite of the long-standing interest in melittin-lipid interactions no systematic thermodynamic study is available. This is probably caused by the complexity of the binding process. Melittin binding to lipid vesicles is fast and occurs within milliseconds but the binding process involves at least 4 steps, namely (i) the electrostatic attraction of the cationic peptide to an anionic membrane surface, (ii) the hydrophobic insertion into the lipid membrane, (iii) the conformational change from random coil to ?-helix and (iv) peptide aggregation in the lipid phase. We have combined microelectrophoresis (measurement of the ?-potential), isothermal titration calorimetry, and circular dichroism spectroscopy to provide a thermodynamic analysis of the individual binding steps. We have compared melittin with a synthetic analog, [D]-V5,8,I17,K21-melittin where ?-helix formation is suppressed and replaced by ?-structure formation. The comparison reveals that the thermodynamic parameters for the membrane-induced ?-helix formation of melittin are identical to those observed earlier for other peptides with an enthalpy hhelix = -0.7 kcal/mol and a free energy of ghelix = -0.2 kcal/mol per peptide residue. These thermodynamic parameters hence appear to be of general validity for lipid-induced membrane folding. As g(helix) is negative, it further follows that helix formation leads to an enhanced membrane binding for the peptides or proteins involved. In this study, melittin binds by approximately 2 orders of magnitude better to the lipid membrane than [D]-V(5,8),I(17),K(21)-melittin which cannot form an alpha-helix. We also found conditions under which the isothermal titration experiment reports only the aggregation process. Melittin aggregation is an entropy-driven process with an endothermic heat of reaction (DeltaH(agg)) of approximately 2 kcal/mol and an aggregation constant of 20-40 M(-1).
Faculties and Departments:05 Faculty of Science > Departement Biozentrum > Former Organization Units Biozentrum > Biophysical Chemistry (Seelig J)
UniBasel Contributors:Seelig, Joachim
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Chemical Society
Note:Publication type according to Uni Basel Research Database: Journal article
Last Modified:22 Mar 2012 14:22
Deposited On:22 Mar 2012 13:30

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