?The interfacial properties of the peptide polybia-mp1 and its interaction with dppc are modulated by lateral electrostatic attractions?

D. DOS SANTOS ALVARES, M.L. FANANI, N. WILKE, J. RUGGIERO NETO.

Puerto Iguazú

Conferencia; 56th International Conference on the Bioscience of lipids; 2015

Bioactive peptides are involved in many important biological processes as part of host defense innate immune system. Polybia-MP1, extracted from the Brazilian wasp Polybia paulista, belongs to a family of antimicrobial peptides and exhibits a broad-spectrum bactericidal activity without being hemolytic and cytotoxic. In the present study, we analyzed the surface properties of the peptide and its interaction with DPPC in Langmuir monolayers. Polybia-MP1 presented a significant interfacial activity on both water and ionic subphases, forming stable monolayers with lateral areas and surface potential suggesting an -helix structure. The peptide occupied larger areas at comparable surface pressures at all conditions different from pure water. Furthermore, only on pure water, DPPC and MP1 co-crystalize forming LC domains with branched shapes. On subphases with high salt concentrations or on acid or basic pHs, the peptide was excluded from the LC domains. All these results indicate that, on pure water, attractive electrostatic interactions between peptides and between DPPC and peptides were present, and the peptides were able to get closer to each other and to co-crystalize with the lipid molecules. We suggest that the residues responsible of the peptide-peptide attraction were the anionic aspartic acids and the cationic lysines, which accommodate in opposite places of the helix, leading to oriented interactions and thereby to branched domains. In summary, we described here the possible lateral interactions for MP1, when the peptide formed pure films and also when mixed with a lipid. We found a complex electrostatic regulation of the peptide-peptide interactions and thereby of the pure and mixed film properties. In this system, the balance between attractive electrostatic interactions and repulsions may be finely tuned by aqueous ionic strength and pH. The results shown here for MP1 may be very probably extrapolated to other lipid/peptides mixtures