Effects of sphingomyelin, cholesterol and zinc ions on the
binding, insertion and aggregation of the amyloid Ab
1)40
peptide in solid-supported lipid bilayers
Savitha Devanathan
1
, Zdzislaw Salamon
1
,Go
¨
ran Lindblom
1
, Gerhard Gro
¨
bner
2
and Gordon Tollin
1
1 Department of Biochemistry and Molecular Biophysics, University of Arizona, Tucson, AZ, USA
2 Department of Biophysical Chemistry, Umea
˚
University, Sweden
The 39–42 amino acid residue amyloid b peptide (Ab)
is a seminal etiologic factor in Alzheimer’s disease
(AD), a member of the large family of neurodegenera-
tive disorders with a common pathology in the form
of aberrant protein folding [1–4]. The unifying theme
for all of these amyloidogenic diseases is the pathologi-
cal conversion of specific proteins into toxic assem-
blies. In the case of AD, its key substance, Ab peptide,
is released as a soluble monomer, but seems to require

er formed from equimolar amounts of DOPC, SM and cholesterol was fol-
lowed using a high-resolution PWR sensor that allowed microdomains to
be observed. Biphasic binding to both domains occurred, but predomin-
antly to the SM-rich domain, initially to the surface and at higher peptide
concentrations within the interior of the bilayer. Again, aggregation was
observed and occurred within both microdomains, resulting in lipid dis-
placement. We attribute the aggregation in the DOPC-enriched domain to
be a consequence of lipid mixing within these microdomains, resulting in
the presence of small amounts of SM and cholesterol in the DOPC micro-
domain. When 1 mm zinc was present, an increase of approximately three-
fold in the amount of peptide association was observed, as well as large
changes in mass and bilayer structure as a consequence of peptide aggrega-
tion, occurring without loss of bilayer integrity. A structural interpretation
of peptide interaction with the bilayer is presented based on the results of
simulation analysis of the PWR spectra.
Abbreviations
Ab, amyloid b
1)40
peptide; AD, Alzheimer’s disease; AFM, atomic force microscopy; DOPC, dioleoylphosphatidylcholine; POPC,
palmitoyloleoylphosphatidylcholine; PWR, plasmon-waveguide resonance; SM, brain sphingomyelin; TFA, trifluoroacetic acid; TFE,
trifluoroethanol.
FEBS Journal 273 (2006) 1389–1402 ª 2006 The Authors Journal compilation ª 2006 FEBS 1389
currently associated with the neuropathological events
occurring in patients with AD [3,7–9]. Nevertheless,
globular and nonfibrillar Ab peptides are continuously
released during normal metabolism in healthy people,
with no problems observed, and therefore fundamental
questions behind the toxic mechanism in AD are
unsolved [10–12]. Recently, the discovery of various
soluble amyloid oligomers having a common structure,

Various lipid membranes have been shown to induce
an electrostatically driven surface accumulation, fol-
lowed by dramatically increased misfolding of Ab,at
rates much higher than in a membrane-free environ-
ment [13–23,25–28]. Membrane components, such as
anionic lipids, gangliosides or cholesterol, were shown
to be involved in various stages of Ab aggregation,
and raft-like neuronal membranes seem to play a signi-
ficant role in the regulation of Ab-production and its
cytotoxic products [20–23,29,30]. Interestingly, brain
lipid composition in patients with AD is significantly
altered, suggesting a link between lipid composition
and increased susceptibility to neuronal cell death
[16,31,32]. Because of its amphipathic nature and the
fact that patients with AD have altered neuronal lipid
compositions [16,17], in the present study we investi-
gated the role of raft-mimicking model neuronal
membranes on the behavior of Ab peptide. Using plas-
mon-waveguide resonance (PWR) spectroscopy [33,34]
we elucidated features of the peptide–membrane inter-
action, which might be important for raft membrane-
dependent aggregation and neurotoxic action, in par-
ticular the presence of sphingomyelin, cholesterol and
zinc ions.
Results and Discussion
In order to characterize the interaction of Ab with lipid
membranes, we used PWR spectroscopy to study the
association with bilayers composed of single lipids, of
binary lipid mixtures, or of a ternary mixture composed
of dioleoylphosphatidylcholine (DOPC) ⁄ sphingomyelin

This is similar to what was observed for the DOPC
bilayer, and occurred with a similar binding affinity
(Fig. 2B; Table 1). However, in the SM bilayer, after
peptide binding and upon further equilibration with
time (up to  15 h), a slow progressive increase in spec-
tral position to higher-incident angles was observed.
These changes, which we attribute to peptide aggrega-
tion, are plotted in Fig. 2C; they occurred exponentially
with a half-time of  4.6 h (Table 2). We have obtained
similar results to these with bilayers composed of
DOPC and SM in a 1 : 1 mole ratio (data not shown).
Factors affecting Ab binding in lipid bilayers S. Devanathan et al.
1390 FEBS Journal 273 (2006) 1389–1402 ª 2006 The Authors Journal compilation ª 2006 FEBS
Interaction of Ab with binary lipid bilayers
As shown by the data in Fig. 3, and by the K
D
values
in Table 1, Ab was bound fivefold more tightly to an
SM bilayer containing cholesterol (1 : 0.35 mole ratio)
and resulted in an approximately twofold larger mag-
nitude in the spectral shifts obtained at 5 lm peptide
concentration (40 mdeg for p-polarization versus 27
mdeg for s-polarization; s-polarized data not shown).
Again, time-dependent aggregation of the peptide
occurred, with a half-time of  4.2 h (Fig. 3C;
Table 2). However, in this case the spectral changes
involved shifts towards lower-incident angles (for
p-polarization, )23 mdeg and for s-polarization,
)9 mdeg; s-polarized data not shown), contrary to that
observed with the SM bilayer in the absence of choles-

for the DOPC-enriched domain (compare Fig. 4B,C).
Table 1. Amyloid b
1)40
peptide (Ab) binding affinities (p-polariza-
tion). DOPC, dioleoylphosphatidylcholine; SM, sphingomyelin.
Bilayer K
D
(lM)
Resonance
shifts (mdeg)
a
DOPC 0.160 ± 0.02 11 ± 1
SM 0.220 ± 0.03 17 ± 1
SM ⁄ cholesterol 0.043 ± 0.01 40 ± 2
DOPC ⁄ SM ⁄ cholesterol
DOPC-rich domain 0.370 ± 0.02 )6±2
SM-rich domain 0.004 ± 0.001 (K
D1
)3±1
0.110 ± 0.01 (K
D2
) )15 ± 2
DOPC ⁄ SM ⁄ cholesterol (+ 1 m
M Zn)
DOPC-rich domain 0.450 ± 0.09 )20 ± 2
SM-rich domain 0.003 ± 0.001 (K
D1
)20±2
0.022 ± 0.001 (K
D2

M
Tris (pH 7.4). Experiments were performed at 25 ± 0.1 °C. (B) Plot
of p-polarized PWR resonance minimum spectral shifts as a func-
tion of the concentration of Ab added to the PWR sample compart-
ment. The binding data were fit by a single hyperbola (solid line),
and the binding affinity values and the magnitude of the spectral
shift are given in Table 1.
S. Devanathan et al. Factors affecting Ab binding in lipid bilayers
FEBS Journal 273 (2006) 1389–1402 ª 2006 The Authors Journal compilation ª 2006 FEBS 1391
It is worth noting that accumulation of peptide at the
microdomain surface, rather than insertion into its
interior, is also possible. We attribute the initial positive
shift to a mass increase resulting from peptide binding
to the bilayer surface, and the subsequent negative shift
to peptide insertion into the bilayer and lipid displace-
ment. The higher spectral resolution allowed us to
observe both of these processes in this experiment. Con-
sistent with the larger spectral shifts for the SM-rich
microdomain, and thus a higher peptide concentration,
the binding affinity of the peptide for this domain was
approximately fourfold larger than for the DOPC-
enriched domain (Table 1). Note that a shift to lower-
incident angles occurred for both microdomains, again
indicating insertion of peptide within the bilayer, pro-
ducing a less densely packed bilayer as a result of
expulsion of lipid molecules. That this occurred in both
microdomains is probably a consequence of the fact
that during microdomain formation a small amount of
SM and cholesterol is mixed into the DOPC portion of
the bilayer, and a small amount of DOPC and choles-

A
0 5 10 15
15
30
45
C
Resonance shifts (mdeg)
Time (h)
Fig. 2. Binding and aggregation of Ab in a
sphingomyelin (SM) bilayer. (A) p-Polarized
plasmon-waveguide resonance (PWR) spec-
tra are shown for an SM bilayer before
(curve 1) and after (curve 2; circles) the addi-
tion of Ab (5 l
M bulk concentration in the
aqueous cell compartment). Curve 3 (trian-
gles) shows the spectrum after equilibration
for 15 h. Other conditions were as in Fig. 1.
(B) Plot of PWR spectral shifts induced by
Ab binding to the bilayer with an increasing
concentration of added peptide. The data
were fit by a single hyperbola, with the
binding constant and total spectral shift
given in Table 1. (C) Plot of the time course
of spectral changes for p-polarization associ-
ated with peptide aggregation. A single
exponential fit to the data is shown (solid
line) with a half-time and total spectral shift
as presented in Table 2.
Table 2. Aggregation kinetics (p-polarization). DOPC, dioleoylphos-

2+
on Ab interaction with a ternary
lipid bilayer
The binding of metal ions, such as Zn
2+
,toAb pep-
tides has been shown to facilitate peptide penetration
of the hydrocarbon core of the membrane and subse-
quent aggregation [22,37]. In order to test the effect of
zinc addition in the present experiments on peptide
binding and bilayer structural changes caused by
aggregation, we used a DOPC ⁄ SM ⁄ cholesterol (1 : 1 : 1
mole ratio) bilayer in contact with a buffer containing
1mm Zn
2+
, present on both sides of the bilayer. The
spectral changes produced as a result of peptide bind-
ing and aggregation in the presence of zinc are shown
in Fig. 5A,B. Control experiments showed that no
PWR spectral changes occurred as a result of Zn
2+
interaction with the lipid bilayer in the absence of pep-
tide. Figure 5A shows the spectral changes for p-polar-
ization at various early time-points up to 200 min after
the addition of 5 lm peptide. The binding and aggre-
gation process was observed to follow biphasic kinet-
ics, with an initial shift to lower-incident angles that
occurred in  30 min, followed at later time-points by
a shift to higher angles accompanied by a decrease in
spectral amplitude for the lower-incident angle reson-

1
Reflectance
Incident angle (deg)
B
012345
0
10
20
30
40
Resonance shifts (mdeg)
Aβ (µM)
0481216
-20
0
20
40
C
Resonance shifts (mdeg)
Time (h)
Fig. 3. Binding and aggregation of Ab in a
SM ⁄ cholesterol (1 : 0.35) bilayer. (A) p-Polar-
ized PWR spectra are shown for a bilayer
before (curve 1) and after (curve 2; squares)
Ab was added to the sample cell (5 l
M bulk
concentration in the aqueous compartment).
Curve 3 (triangles) shows the spectrum
after equilibration for 15 h. Other conditions
were as in Fig. 1. (B) Plot of the spectral

zinc on the formation of a helical peptide structure that
facilitates insertion and pore formation as a result of
aggregation [22,37,38]. Furthermore, the atomic force
microscopy (AFM) studies of Lin et al. [39], on solid-
supported bilayers, have shown that the interaction of
Ab results in the formation of conducting ion channels
that have rectangular or hexagonal shapes with four or
six subunits, are 80–120 A
˚
in diameter and protrude
 10 A
˚
from the bilayer surface. The large PWR spec-
tral changes shown in Fig. 5 are consistent with struc-
tures of this magnitude inserted into the bilayer.
Fig. 4. Binding and aggregation of Ab in a DOPC ⁄ SM ⁄ cholesterol (1 : 1 : 1) bilayer. Spectra were obtained using a high-resolution sensor.
Other experimental conditions are as given in the legend to Fig. 1. (A) p-Polarized PWR spectra are shown for the membrane before (curve
1) and after (curve 2; squares) addition of the peptide (5 l
M bulk concentration in the aqueous cell compartment). Based on previous results
[35], the resonance at smaller-incident angles is ascribed to a DOPC-enriched microdomain, and the resonance at larger incident angles to
an SM-enriched microdomain. The initial addition of peptide resulted in binding to both microdomains, but to a larger extent in the SM-rich
domain. Spectra are also shown after the sample had equilibrated for 3 h (curve 3; circles) and 15 h (curve 4; triangles). These changes are
ascribed to peptide aggregation. (B,C) Plots of initial peptide binding, resulting in shifts to larger angles (inset to B) and binding at higher con-
centrations resulting in shifts to smaller angles. Binding to the SM-rich domain is shown in (B) and to the DOPC-rich domain in (C). Data
were fit with three hyperbolic curves (solid lines), yielding the affinity constants and spectral shifts in Table 1. (D) Plots of the time course of
spectral changes for the DOPC-rich microdomain (open triangles) and the SM-rich microdomain (closed triangles) associated with peptide
aggregation. Solid lines correspond to single exponential fits, with half-times and total shifts given in Table 2.
Factors affecting Ab binding in lipid bilayers S. Devanathan et al.
1394 FEBS Journal 273 (2006) 1389–1402 ª 2006 The Authors Journal compilation ª 2006 FEBS
Spectral simulation and structural modeling

occurred mainly in the SM-rich microdomain (data not shown). With time, additional resonance shifts occurred, mainly in the SM-rich micro-
domain, along with large changes in amplitude. The resonance for the DOPC-rich domain diminished in intensity, whereas that for the SM-
rich domain increased in intensity and large shifts to longer angles occurred. Note that the t ¼ 208 min resonance is repeated in both panels
for reference purposes. (C,D) Plots of initial peptide binding, resulting in shifts to larger angles (inset to C) and binding at higher concentra-
tions resulting in shifts to smaller angles. Binding to the SM-rich domain is shown in (C) and to the DOPC-rich domain in (D). Data were fit
with three hyperbolic curves (solid lines) to yield affinity constants and spectral shifts as given in Table 1. Initial insertion into the SM-rich
domain was followed by incorporation into both microdomains.
S. Devanathan et al. Factors affecting Ab binding in lipid bilayers
FEBS Journal 273 (2006) 1389–1402 ª 2006 The Authors Journal compilation ª 2006 FEBS 1395
membrane properties have been changed by the pep-
tide–bilayer interaction. This is accomplished by evalu-
ation of the optical parameters for the lipid layer
before and after binding of peptide and subsequent
aggregation, and of the layer composed of peptide (or
a portion of the peptide) that extends beyond the lipid
surface. Both p- and s-polarized data were used in such
simulations. Figure 7 shows an example of the simula-
ted spectra superimposed on the experimental spectra,
obtained with s-polarized red light (k ¼ 632.8 nm).
The optical parameters resulting from such simulations
for bilayers composed of DOPC, of SM and of
SM ⁄ cholesterol are summarized in Tables 3–5 for the
binding and aggregation processes. The error limits
shown in these tables correspond to the standard
errors obtained from the fitting procedure. It must be
noted that we have not been able to satisfactorily
simulate the spectra obtained with the DOPC ⁄
SM ⁄ cholesterol bilayers, with and without zinc, using
the high-resolution resonator. This requires additional
information about the effects of varying amounts of

entials; half-times and spectral shifts are given in Table 2.
61.54 61.64 61.74
0.75
0.85
0.95
Incident an
g
le, de
g
Reflectance
1
2
3
Fig. 7. Examples of simulated spectra (solid lines) superimposed
on experimental spectra (symbols), obtained with a SM ⁄ cholesterol
membrane using s-polarized red light. Spectra are shown for the
membrane before (curve 1) and after (curve 2) addition of peptide.
Curve 3 was obtained after aggregation.
Table 3. Optical parameters of lipid bilayers prior to Ab binding.
DOPC, dioleoylphosphatidylcholine; n
p
, p-polarized refractive index;
n
s
, s-polarized refractive index; SM, sphingomyelin; t
av
, average
thickness.
Bilayer n
p

structures which are arranged in the peptide layer in a
random way, thereby creating an average isotropic dis-
tribution of conformations. It is worth noting that
such anisotropies can result from either molecular con-
formation or molecular orientation, or both; these can-
not be distinguished by the present methods.
In none of the three membrane systems did the ini-
tial binding of peptide cause any significant changes in
the lipid bilayer parameters (Table 4). This suggests
that the peptide was not anchored deeply within these
membranes, indicating that the bulk of the peptide
mass remained largely on the surface of the membrane.
However, the peptide layer was appreciably different
for the SM ⁄ cholesterol membrane, having a higher
mass density, a significant anisotropy (n
p
> n
s
), and a
larger thickness. Thus, more peptide was bound when
cholesterol was included in the bilayer, and the struc-
ture of the peptide layer was different. In order to
explain the anisotropic nature of the peptide layer, it
seems reasonable to assume that some of bound pep-
tides had an extended conformation (b-sheet like) and
bound with their long axis perpendicular to the plane
of the lipid membrane. Furthermore, the 4.7 nm thick-
ness of the peptide layer indicates that the hydropho-
bic tail of the peptide must be buried within the lipid
bilayer. This type of arrangement of the bound peptide

Bilayer
Lipid layer (after binding) Peptide layer (after binding)
n
p
(± 0.003) n
s
(± 0.002) t
av
(nm) (± 0.2) n
p
(± 0.005) n
s
(± 0.005) t
av
(nm) (± 0.2)
DOPC 1.460 1.445 5.0 1.340 1.340 3.0
SM 1.520 1.450 5.8 1.365 1.365 3.0
SM ⁄ chol 1.555 1.522 6.2 1.420 1.400 4.7
Table 5. Optical parameters of lipid and peptide layers after amyloid b
1)40
peptide (Ab) aggregation. chol, cholesterol; DOPC, dioleoylphos-
phatidylcholine; n
p
, p-polarized refractive index; n
s
, s-polarized refractive index; SM, sphingomyelin; t
av
, average thickness.
Bilayer
Lipid layer (after aggregation) Peptide layer (after aggregation)

of the surfaces of each of the bilayers. This requires
further study.
The differences between the membranes increased
further with time after the initial binding process. As
noted above, and as shown in Table 5, after 15 h there
were no significant changes in either the bilayer or the
peptide layer with the DOPC membrane (i.e. no pep-
tide aggregation occurred). In contrast, changes
occurred in both of these layers with the SM mem-
brane. Thus, the surface mass density of the peptide
layer decreased, as reflected by the smaller value of n
s
,
and a significant refractive index anisotropy was
induced (n
p
> n
s
). A corresponding increase in the
mass density in the lipid bilayer occurred, without a
significant change in anisotropy. These results clearly
indicate that some peptide mass was inserted into the
lipid membrane, and that the mass distribution within
the peptide layer was altered. In order for the latter to
occur, a significant conformational rearrangement
must take place, involving either creating more aniso-
tropic conformations or reorganizing the existing
anisotropic conformations so as to create long-range
molecular order, or both. A plausible interpretation of
these effects is that some of the surface-bound peptide

The presence of cholesterol facilitates peptide insertion
into the bilayer and promotes the aggregation process.
This leads to the formation of a less densely packed
bilayer. The presence of Zn
2+
also enhances insertion
and aggregation, and promotes large bilayer structural
changes by peptide aggregates resulting in a more por-
ous membrane. The large effects of SM and cholesterol
on peptide insertion and aggregation are consistent
with the reported occurrence of the amyloid precursor
protein and Ab in neuronal membrane rafts [20–
23,29,30].
Experimental procedures
Materials
Solid-supported lipid bilayers (DOPC, SM, cholesterol and
their mixtures; Avanti Polar Lipids, Birmingham, AL,
USA) were made using solutions of either the single lipid
components or mixtures containing various molar ratios
of lipids (10 mgÆmL
)1
total lipid concentration) in buta-
nol ⁄ squalene (10 : 0.1, v ⁄ v). The buffer solution in contact
with the bilayer in the sample cell for all the experiments
was 10 mm Tris (pH 7.4) at 25 °C, either in the absence of
additional salt ions or in the presence of 1 mm Zn
2+
ions.
The 40-residue amyloid peptide (Ab
1)40

The PWR spectrum can be described by the depth, the
half-width and the angular position of the resonances,
which are determined by the optical characteristics of the
sensor and the immobilized molecules at the plasmon
excitation wavelength. Molecular interactions or composi-
tion changes occurring at the surface are detected as
changes in these spectral characteristics in real time.
Thus, PWR provides a means to directly measure the
binding, insertion and aggregation of molecules, either at
the lipid bilayer surface or upon incorporation into the
bilayer.
Formation of lipid membranes and peptide
incorporation
The principles of creating a self-assembled single solid-sup-
ported planar lipid bilayer membrane on a PWR resonator
surface have been described in previous publications
[45,46]. Here, we will briefly review those principles. Bilay-
ers were prepared by spreading a small amount of the
appropriate lipid solution in the butanol ⁄ squalene solvent
onto a 2 mm orifice in a Teflon block, separating the silica
surface of the PWR resonator from the aqueous compart-
ment. The hydrated silica surface attracts the polar head
groups of the lipid to form a monolayer with the hydrocar-
bon tails oriented towards the excess lipid solution. Bilayer
formation is spontaneously initiated when the sample com-
partment is filled with an aqueous buffer solution, resulting
in a thinning process to form the second monolayer. A
plateau-Gibbs border, consisting of an annulus of excess
lipid solution, anchors the bilayer to the Teflon block. This
border allows lipid molecules to be transferred into or out

and in the bilayer distribution of such microdomains from
one experiment to another (i.e. in the ratio between the
lipid ordered and disordered phases), as well as in the
sampling of such microdomains by the laser beam [35]. This
can result in variability in the spectral line shape from
Fig. 8. Schematic diagram of a PWR apparatus. A lipid bilayer with
inserted peptides is shown immobilized on the resonator surface.
The presence of a silica layer allows excitation by both p-polarized
and s-polarized light. Excitation produces an evanescent electro-
magnetic field localized on the outer silica surface; molecules
immobilized on this surface interact with the field causing spectral
changes. Adapted from a previous publication [44].
S. Devanathan et al. Factors affecting Ab binding in lipid bilayers
FEBS Journal 273 (2006) 1389–1402 ª 2006 The Authors Journal compilation ª 2006 FEBS 1399
experiment to experiment (compare, for example, Fig. 4A
with Fig. 5A). The diffusion of the microdomains within
the bilayer is relatively slow and occurs in the order of min-
utes [47,48]. PWR spectra were taken at regular intervals to
follow the equilibration processes involved in bilayer forma-
tion occurring on the resonator surface.
After bilayer membrane equilibration, lyophilized TFA ⁄
TFE-pretreated Ab, freshly dissolved in aqueous buffer,
was added in small (microliter) aliquots to the aqueous
compartment of the PWR cell (total volume  1 mL), and
binding of peptide to the bilayer was observed as a change
in the resonance position minimum, with time, for both
p- and s-polarization. In all experiments, the total Ab con-
centration in the sample cell after these additions was 5 lm.
The binding process reached equilibrium  5 min after pep-
tide addition. Inasmuch as time-dependent aggregation of

by changes in the anisotropic ordering of peptide molecules
and influences on the lipid bilayer structure. This has the
advantage of allowing information to be obtained concern-
ing such structural modifications. In order to determine
whether aggregation required additional peptide to be
recruited from the aqueous medium, some experiments were
carried out in which the excess peptide in solution was
removed by washing with fresh buffer subsequent to pep-
tide binding to the bilayer. These experiments resulted in
spectral shifts (owing to aggregation) with time that were
approximately the same magnitude as those obtained with-
out washing. Thus, we conclude that aggregation proceeded
using peptide that was already bound to the bilayer. All
PWR experiments reported here were carried out using a
Beta-PWR instrument (Proterion Corp., Piscataway, NJ,
USA) using either 543.5 nm or 632.8 nm wavelength excita-
tion. Both wavelengths yielded similar results. As performed
in previous studies [35,36], spectral simulation was used to
analyze some of the PWR data to provide insights into the
structural consequences of peptide binding and aggregation.
Acknowledgements
This work was supported, in part, by grants from the
US National Institutes of Health (GM 59630 to G.T.
and Z.S.), from the Amgen Corporation (to G.T., Z.S.
and S.D.), from the Swedish Research Council (to
G.L. and G.G.), from the Umea
˚
University Biotechno-
logy Fund (to G.G.) and from the Alzheimer Founda-
tion (to G.G.).

Biochemistry 39, 10831–10839.
9 Klein WL, Stine WB Jr & Teplow DB (2004) Small
assemblies of unmodified amyloid beta-protein are the
Factors affecting Ab binding in lipid bilayers S. Devanathan et al.
1400 FEBS Journal 273 (2006) 1389–1402 ª 2006 The Authors Journal compilation ª 2006 FEBS
proximate neurotoxin in Alzheimer’s disease. Neurobiol
Aging 25, 569–580.
10 Kayed R, Head E, Thompson JL, McIntire TM, Milton
SC, Cotman CW & Glabe C (2003) Common structure
of soluble amyloid oligomers implies common mechan-
ism of pathogenesis. Science 300, 486–489.
11 De Strooper B & Ko
¨
nig G (2001) An inflammatory
drug prospect. Nature 414, 159–160.
12 Yuan J & Yankner BA (2000) Apoptosis in the nervous
system. Nature 407, 802–809.
13 Simons M, Keller P, De Strooper B, Beyreuther K,
Dotti CG & Kimons K (1998) Cholesterol depletion
inhibits the generation of beta-amyloid in hippocampal
neurons. Proc Natl Acad Sci USA 95, 6460–6464.
14 Pettegrew JW, Panchalingam K, Hamilton RL &
McClure RJ (2001) Brain membrane phospholipid
alterations in Alzheimer’s disease. Neurochem Res 26,
771–782.
15 Kracun I, Kalanj S, Cosovic C, Talanhranilovic J &
Cosovic C (1992) Cortical distribution of gangliosides in
Alzheimer’s disease. Neurochem Int 20, 433–438.
16 Waschuk SA, Elton EA, Darabie AA, Fraser PE &
McLaurin J (2001) Cellular membrane composition

heimer’s disease. Biochim Biophys Acta 1610, 281–290.
22 Curtain CC, Ali FE, Smith DG, Bush AI, Masters CL
& Barnham KJ (2003) Metal ions, pH, and cholesterol
regulate the interactions of Alzheimer’s disease amyloid-
beta peptide with membrane lipid. J Biol Chem 278 ,
2977–2982.
23 Kremer JJ, Pallitto MM, Sklansky DJ & Murphy RM
(2000) Correlation of beta-amyloid aggregate size and
hydrophobicity with decreased bilayer fluidity of model
membranes. Biochemistry 39, 10309–10318.
24 Demeester N, Baier G, Enzinger C, Goethals M, Van-
dekerckhove J, Rosseneu M & Labeur C (2000) Apop-
tosis induced in neuronal cells by C-terminal amyloid
beta-fragments is correlated with their aggregation prop-
erties in phospholipid membranes. Mol Membr Biol 17,
219–228.
25 Koppaka V & Axelsen PH (2000) Accelerated accumu-
lation of amyloid beta proteins on oxidatively damaged
lipid membranes. Biochemistry 39, 10011–10016.
26 Kawahara M, Kuroda Y, Arispe N & Rojas E (2000)
Alzheimer’s beta-amyloid, human islet amylin, and pri-
on protein fragment evoke intracellular free calcium ele-
vations by a common mechanism in a hypothalamic
GnRH neuronal cell line. J Biol Chem 275, 14077–
14083.
27 Yip CM & McLaurin J (2001) Amyloid-beta peptide
assembly: a critical step in fibrillogenesis and membrane
disruption. Biophys J 80, 1359–1371.
28 Yip CM, Darabie AA & McLaurin J (2002) Abeta42-
peptide assembly on lipid bilayers. J Mol Biol 318, 97–

Biophys J 73, 2791–2797.
34 Salamon Z & Tollin G (2001) Plasmon resonance spec-
troscopy: probing molecular interactions at surfaces and
interfaces. Spectroscopy 15, 161–175.
35 Salamon Z, Devanathan S, Alves I & Tollin G (2005)
Plasmon-waveguide resonance studies of lateral segrega-
tion of lipids and proteins into microdomains (rafts) in
solid-supported bilayers. J Biol Chem 280, 11175–11184.
36 Alves I, Salamon Z, Hruby V & Tollin G (2005) Ligand
modulation of lateral segregation of a G-protein-
coupled receptor into lipid microdomains in
S. Devanathan et al. Factors affecting Ab binding in lipid bilayers
FEBS Journal 273 (2006) 1389–1402 ª 2006 The Authors Journal compilation ª 2006 FEBS 1401
sphingomyelin ⁄ phosphatidylcholine solid-supported
bilayers. Biochemistry 44, 9168–9178.
37 Curtain CC, Ali F, Volitakis I, Cherny RA, Norton RS,
Beyreuther K, Barrow CJ, Masters CL, Bush AI & Barn-
ham KJ (2001) Alzheimer’s disease amyloid-beta binds
copper and zinc to generate an allosterically ordered
membrane-penetrating structure containing superoxide
dismutase-like subunits. J Biol Chem 276, 20466–20473.
38 Bush AI (2003) The metallobiology of Alzheimer’s dis-
ease. Trends Neurosci 26, 207–214.
39 Lin H, Bhatia R & Ratneshwar L (2001) Amyloid beta
protein forms ion channels: implications for Alzheimer’s
disease pathophysiology. FASEB J 15 , 2433–2444.
40 Ji S-R, Wu Y & Sui S-F (2002) Cholesterol is an impor-
tant factor affecting the membrane insertion of beta-amy-
loid peptide (A beta 1–40), which may potentially inhibit
the fibril formation. J Biol Chem 277, 6273–6279.

48 Ora
¨
dd G, Westerman PW & Lindblom G (2005) Lateral
diffusion coefficients of separate lipid species in a tern-
ary raft-forming bilayer: a pfg-NMR multinuclear
study. Biophys J 89, 315–320.
49 Ege C & Lee KY (2004) Insertion of Alzheimer’s A beta
40 peptide into lipid monolayers. Biophys J 87, 1732–
1740.
Factors affecting Ab binding in lipid bilayers S. Devanathan et al.
1402 FEBS Journal 273 (2006) 1389–1402 ª 2006 The Authors Journal compilation ª 2006 FEBS