CONFORMATION AND INTERACTIONS OF BOMBOLITIN-I ANALOGS WITH SDS MICELLES AND PHOSPHOLIPID-VESICLES - CD, FLUORESCENCE, 2-DIMENSIONAL NMR ANDCOMPUTER-SIMULATIONS
M. Chorev et al., CONFORMATION AND INTERACTIONS OF BOMBOLITIN-I ANALOGS WITH SDS MICELLES AND PHOSPHOLIPID-VESICLES - CD, FLUORESCENCE, 2-DIMENSIONAL NMR ANDCOMPUTER-SIMULATIONS, Biopolymers, 36(4), 1995, pp. 473-484
Bombolitins are five structurally related heptadecapeptides acting at
the membrane level able to lyse erythrocytes and liposomes and to enha
nce the activity of phospholipase A(2) (PLA(2)). In the presence of SD
S or phospholipid vesicles bombolitins are able to form amphiphilic al
pha-helical structures and this property seems to be the major determi
nant of bioactivity. In order to test the model of interaction between
bombolitin I and membranes, an analogue was synthesized in which all
the lysines were replaced by arginine: et-Leu-Ala-Arg-Ile-Gly-Arg-Val-
Leu-Ala-His-Val-NH2 ([Arg(2,9,12), Ile(10)] bombolitin I). The design
of this sequence allowed the synthesis of a second analogue through a
specific postsynthetic dansylation at epsilon-amino group of a lysine
residue replacing the original leucine residue at position 7. The firs
t analogue was fully characterized by CD and two-dimensional nmr in th
e presence of SDS or phospholipid vesicles. The peptide folds into an
amphilphilic alpha-helical conformation with the helical segment spann
ing the central part of the sequence from Ile(3) to His(16). This beha
vior is identical to that observed for the native sequence. The replac
ement of lysine residues by arginine has no detectable effect on the c
onformational preference of the peptide chain. By CD and fluorescence
spectroscopy measurements, the fluorophore-containing analogue [Arg(2,
9,12), Lys(7) (epsilon-dansyl)] bombolitin I also folded into the alph
a-helical conformation in the presence of SDS micelles or phospholipid
vesicles. In particular, the dansyl fluorophore, which is located app
roximately in the middle of the apolar surface of the amphiphilic heli
x, is clearly buried in a hydrophobic environment when the peptide is
bound to phospholipid vesicles. These findings support the hypothesis
that the peptide helices are oriented parallel to the vesicle surface.
(C) 1995 John Wiley & Sons, Inc.