Binding of basic amphipathic peptides to neutral phospholipid membranes: a thermodynamic study applied to dansyl-labeled melittin and substance P analogues.
A thermodynamic approach is proposed to quantitatively analyze the binding isotherms of peptides to model membranes as a function of one adjustable parameter, the actual peptide charge in solution z(p)+. The main features of this approach are a theoretical expression for the partition coefficient calculated from the molar free energies of the peptide in the aqueous and lipid phases, an equation proposed by S. Stankowski [(1991) Biophysical Journal, Vol. 60, p. 341] to evaluate the activity coefficient of the peptide in the lipid phase, and the Debye-Hückel equation that quantifies the activity coefficient of the peptide in the aqueous phase. To assess the validity of this approach we have studied, by means of steady-state fluorescence spectroscopy, the interaction of basic amphipathic peptides such as melittin and its dansylcadaverine analogue (DNC-melittin), as well as a new fluorescent analogue of substance P, SP (DNC-SP) with neutral phospholipid membranes. A consistent quantitative analysis of each binding curve was achieved. The z(p)+ values obtained were always found to be lower than the physical charge of the peptide. These z(p)+ values can be rationalized by considering that the peptide charged groups are strongly associated with counterions in buffer solution at a given ionic strength. The partition coefficients theoretically derived using the z(p)+ values were in agreement with those deduced from the Gouy-Chapman formalism. Ultimately, from the z(p)+ values the molar free energies for the free and lipid-bound states of the peptides have been calculated.
Pérez-Payá
E
E
Departament de Bioquímica i Biologia Molecular, Universitat de Valencia, Spain.
Porcar
I
I
Gómez
C M
CM
Pedrós
J
J
Campos
A
A
Abad
C
C
D000595:Amino Acid Sequence; D003619:Dansyl Compounds; D004563:Electrochemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D008555:Melitten / Q000031:analogs & derivatives* / Q000737:chemistry*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013373:Substance P / Q000031:analogs & derivatives* / Q000737:chemistry*; D013816:Thermodynamics; D011503:Transglutaminases
D003619:Dansyl Compounds; D008051:Lipid Bilayers; D008555:Melitten; D013373:Substance P; D011503:Transglutaminases