A high-sensitivity differential scanning calorimetric study of the interaction of melittin with dipalmitoylphosphatidylcholine fused unilamellar vesicles

Thomas D. Bradrick, Ernesto I Freire, S. Georghiou

Research output: Contribution to journalArticle

Abstract

High-sensitivity differential scanning calorimetry has been used to examine the interaction of bee venom melittin with dipalmitoylphosphatidylcholine fused unilamellar vesicles. Experiments were performed under conditions for which melittin in solution is either monomeric (in low salt) or tetrameric (in high salt). It was found that under both sets of conditions melittin abolishes the pretransition at a relatively high lipid-to-protein molar incubation ration, Ri (about 200) and that at intermediate values of Ri, it broadens the main transition profile and reduces the transition enthalpy. This provides evidence which suggests that melittin is at least partially inserted into the apolar region of the bilayer. Evident at low values of Ri are two peaks in the lipid thermal transition profiles, which may arise from a heterogeneous population of lipid vesicles formed through fusion induced by melittin, or by lipid phase separation. For those profiles which exhibited only one peak, transition enthalpies, normalized to those of the lipid in the absence of the protein, are plotted vs. the bound protein-to-lipid molar ratios for the experiments performed under the conditions which give monomeric and tetrameric melittin in solution. These plots yield straight lines, the slopes of which give the number of lipid molecules each protein molecule excludes from participating in the phase transition. These were found to be 9.9 ± 0.7 and 4.1 ± 0.5 for monomeric and tetrameric melittin, respectively. The results are discussed in terms of possible models for the binding of melittin to phospholipid vesicles. For simple hexagonal packing of lipid molecules, incorporation as an aggregate is favored when melittin is tetrameric in solution, whereas incorporation as a monomer is favored when melittin is monomeric in solution. For low-salt solutions, evidence is obtained for the contribution of free melittin to lipid fusion, perhaps by the formation of protein bridges between apposed vesicles.

Original languageEnglish (US)
Pages (from-to)94-102
Number of pages9
JournalBBA - Biomembranes
Volume982
Issue number1
DOIs
StatePublished - Jun 26 1989

Fingerprint

Melitten
1,2-Dipalmitoylphosphatidylcholine
Unilamellar Liposomes
Scanning
Lipids
Salts
Proteins
Molecules
Enthalpy
Fusion reactions
Bee Venoms
Phase Transition
Differential Scanning Calorimetry
Phase separation
Differential scanning calorimetry
Phospholipids
Hot Temperature
Monomers

Keywords

  • Boundary lipid
  • DSC
  • Melittin
  • Protein aggregation
  • Protein-lipid interaction

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Cell Biology
  • Medicine(all)

Cite this

A high-sensitivity differential scanning calorimetric study of the interaction of melittin with dipalmitoylphosphatidylcholine fused unilamellar vesicles. / Bradrick, Thomas D.; Freire, Ernesto I; Georghiou, S.

In: BBA - Biomembranes, Vol. 982, No. 1, 26.06.1989, p. 94-102.

Research output: Contribution to journalArticle

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