Conformational study of [Met5]enkephalin-Arg-Phe in the presence of phosphatidylserine vesicles.
The interaction of [Met5]enkephalin-Arg.Phe with phosphatidylserine (PtdSer) was studied by circular dichroism (CD), two-dimensional nuclear magnetic resonance spectroscopy, hybrid distance geometry simulated annealing (DG-SA) and molecular dynamics (MD) calculations. The very low solubility of [Met5]enkephalin-Arg-Phe and the instability of the solution containing PtdSer vesicles at low pH values did not allow us to observe the amide proton resonances in the usual two-dimensional NMR work. NOESY cross-peaks of protons of side chains from two-dimensional NMR were converted into distances which were used as restraints for modelling with DG-SA and MD. Our results indicate that, in aqueous solutions at pH 7.68 [Met5]enkephalin-Arg-Phe exists in the absence of PtdSer as a random distribution of conformers, whereas in the presence of PtdSer it adopts conformations containing a common orientation of the bonds of C alpha 2, C alpha 3, C alpha 4, and C alpha 5, although different orientations of the peptide planes are consistent with the results. Two of the reported conformers from MD simulations are characterized by the presence of a 2<--4 gamma and inverse gamma turns centered on Gly3. A gradual decline of order was observed when moving from the central moiety of the peptide to both the N-terminus and C-terminus. Finally, the DG-SA and MD calculations resulted in a structure such that the orientation of the Phe4 and Met5 side chains favours hydrophobic interactions with the apolar portion of the PtdSer vesicle to form a hydrophobic cluster. These data support the hypothesis of a role of lipids to modify the conformation of [Met5]enkephalin-Arg-Phe to permit the interactions with the receptor site.
D'Alagni
M
M
Centro di Studio per la Chimica dei Recettori e delle Molecole Biologicamente Attive, C. N. R., Roma, Italy.
Delfini
M
M
Di Nola
A
A
Eisenberg
M
M
Paci
M
M
Roda
L G
LG
Veglia
G
G
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000737:chemistry; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010718:Phosphatidylserines / Q000737:chemistry*; D011487:Protein Conformation; D013816:Thermodynamics
D008081:Liposomes; D010718:Phosphatidylserines; D004744:Enkephalin, Methionine; C027511:enkephalin-Met, Arg(6)-Phe(7)-