Energetics and partition of two cecropin-melittin hybrid peptides to model membranes of different composition
Margarida Bastos 1*, Guangyue Bai 1, Paula Gomes 1, David Andreu 2, Erik Goormaghtigh 3 and Manuel Prieto 4
1 CIQ(UP) Faculty of Sciences, University of Porto
2 Proteomics & Protein Chemistry, DCEXS-UPF-PRBB, E-08003 Barcelona, Spain
3 Structure and Function of Biological Membranes, Université Libre de Bruxelle, Belgique
4 CQFM, Instituto Superior Técnico, UTL, P-1049-001 Lisboa, Portugal
* To whom correspondence should be addressed. E-mail: mbastos{at}fc.up.pt.
Submitted on August 3, 2007
Revised on September 3, 2007
Accepted on 23 October 2007
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Abstract |
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The energetics and partition of two hybrid peptides of cecropin A and melittin [CA(1-8)M(1-18) and CA(1-7)M(2-9)] with liposomes of different composition was studied by Isothermal Titration Calorimetry (ITC), Time-Resolved Fluorescence Spectroscopy (TRFS) and Surface Plasmon Resonance (SPR). The study was carried out with large unilamellar vesicles (LUVs) of three-sn-glycero-3-phosphocholine (DMPC),1,2-dimyristoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DMPG) and a 3:1 binary mixture of DMPC/DMPG, in a wide range of peptide-to-lipid ratios (P:L). The results are compatible with a model involving a strong electrostatic surface interaction between the peptides and the negatively charged liposomes, giving rise to aggregation and precipitation. A correlation is observed in the calorimetric experiments between the observed events and charge neutralization, for negatively charged and mixed membranes. In the case of zwitterionic membranes, a very interesting case study was obtained with the smaller peptide, CA(1-7)M(2-9). The calorimetric results obtained for this peptide in a large range of peptide:lipid ratios can be interpreted on the basis of an initial and progressive surface coverage until a threshold concentration, where the orientation changes from parallel to perpendicular to the membrane, followed by pore formation and eventually membrane disruption. The importance of negatively charged lipids on the discrimination between bacterial and eukaryotic membranes is emphasized.
Key Words:
ITC, SPR, TRFS, antimicrobial peptides, calorimetry, cecropin-melittin hybrid
