Biomimetic organization: Octapeptide self-assembly into nanotubes of viral capsid-like dimension.

Abstract

The controlled self-assembly of complex molecules into well defined hierarchical structures is a promising route for fabricating nanostructures. These nanoscale structures can be realized by naturally occurring proteins such as tobacco mosaic virus, capsid proteins, tubulin, actin, etc. Here, we report a simple alternative method based on self-assembling nanotubes formed by a synthetic therapeutic octapeptide, Lanreotide in water. We used a multidisciplinary approach involving optical and electron microscopies, vibrational spectroscopies, and small and wide angle x-ray scattering to elucidate the hierarchy of structures exhibited by this system. The results revealed the hexagonal packing of nanotubes, and high degree of monodispersity in the tube diameter (244 A) and wall thickness (approximately equal to 18 A). Moreover, the diameter is tunable by suitable modifications in the molecular structure. The self-assembly of the nanotubes occurs through the association of beta-sheets driven by amphiphilicity and a systematic aromatic/aliphatic side chain segregation. This original and simple system is a unique example for the study of complex self-assembling processes generated by de novo molecules or amyloid peptides.

Full text

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Biomimetic organization: Octapeptide self-assembly
into nanotubes of viral capsid-like dimension
Ce ´line Vale ´ry†, Maı ¨te ´ Paternostre†‡§, Bruno Robert‡, Thadde ´e Gulik-Krzywicki¶, Theyencheri Narayanan?,
Jean-Claude Dedieu¶, Ge ´rard Keller†, Maria-Luisa Torres††, Roland Cherif-Cheikh††, Pilar Calvo††, and Franck Artzner†§‡‡
†Unite ´ Mixte de Recherche 8612, Centre National de la Recherche Scientifique, Faculte ´ de Pharmacie, 5 Rue J.B. Cle ´ment, 92296 Châtenay-Malabry Cedex,
France;‡Service de Biophysique des Fonctions Membranaires, De ´partement de Biologie Joliot Curie, Unite ´ de Recherche Associe ´e 2096, Centre National
de la Recherche Scientifique, Commissariat a ` l’Energie Atomique–Saclay, 91191 Gif-sur-Yvette, France;¶Centre de Ge ´ne ´tique Mole ´culaire, Centre
National de la Recherche Scientifique, 91198 Gif-sur-Yvette, France;?European Synchrotron Radiation Facility, BP 220, 38403 Grenoble Cedex,
France; and††Ipsen Pharma S.A., Ctra. Laurea ` Miro ´ 395, 08980-Sant Feliu de Llobregat, Barcelona, Spain
Edited by Daniel Branton, Harvard University, Cambridge, MA, and approved July 2, 2003 (received for review January 31, 2003)
The controlled self-assembly of complex molecules into well de-
fined hierarchical structures is a promising route for fabricating
nanostructures. These nanoscale structures can be realized by
naturally occurring proteins such as tobacco mosaic virus, capsid
proteins, tubulin, actin, etc. Here, we report a simple alternative
methodbasedonself-assemblingnanotubesformedbyasynthetic
therapeutic octapeptide, Lanreotide in water. We used a multidis-
ciplinary approach involving optical and electron microscopies,
vibrational spectroscopies, and small and wide angle x-ray scat-
tering to elucidate the hierarchy of structures exhibited by this
system. The results revealed the hexagonal packing of nanotubes,
and high degree of monodispersity in the tube diameter (244 Å)
and wall thickness (?18 Å). Moreover, the diameter is tunable by
suitable modifications in the molecular structure. The self-assem-
bly of the nanotubes occurs through the association of ?-sheets
driven by amphiphilicity and a systematic aromatic?aliphatic side
chain segregation. This original and simple system is a unique
example for the study of complex self-assembling processes gen-
erated by de novo molecules or amyloid peptides.
T
and has wide ranging applications in biotechnology and mate-
rials sciences (1). In fact, characteristic lengths ?100 nm are not
easily accessible at present by lithographic techniques, but can be
realized with biological self-assemblies such as tobacco mosaic
virus, capsid proteins (2), tubulin (3), or actin (4, 5). These
proteins under appropriate conditions possess the unique capa-
bility to form long filaments with a well defined diameter.
However, the fabrication cost often restricts their potential
interest in practical applications. Therefore, a simple alternative
route has been emerged based on de novo molecules that
self-organize in a programmed way (6–11). The design of such
biomimetic systems requires the understanding of the relation-
ship between the molecular structure and the self-assembly
process of the nanostructures. This inspiration from natural
fibers is difficult to implement when the building blocks them-
selves are complex, as in the case of proteins. Up to now, no
simple synthetic molecule was able to self-assemble into hollow
nanotubes with well defined characteristic length in the range of
20–30 nm.
Lanreotideisanoctapeptidesynthesizedasagrowthhormone
inhibitor. Lanreotide forms hydrogels (Autogel), which are
already used in acromegaly treatment as s.c. long-acting implants
(12). Here we report the molecular and supramolecular orga-
nization of self-assembling nanotubes formed by Lanreotide in
water (10% wt?wt, acetate salt). We chose a multidisciplinary
approach, by combining polarized light microscopy, electron
microscopy, vibrational spectroscopies, small and wide angle
x-ray scattering (SAXS and WAXS, respectively) to elucidate the
hierarchical structures formed by this system. The nanotubes are
remarkably monodisperse, with a diameter of 244 Å and a
wall thickness of ?18 Å. The study of a Lanreotide derivative
he ability of simple molecules to spontaneously organize into
well defined nanostructures is of fundamental importance
indicates the possibility to control the diameter of these tubes
from the molecular structure. The self-assembly of these nano-
tubes occurs through the association of ?-sheets driven by
amphiphilicity and a systematic aromatic?aliphatic side chain
segregation. This original and simple system is a unique example
ofmoleculesabletoself-organizeintowelldefinednanostucture.
The resolution of the structure at the molecular scale highlights
the simplicity of the interactions involved in the self-assembly
process, and could find implication for ?-amyloid fibers or de
novo self-assemblies.
Materials and Methods
Materials. Cyclic Lanreotide of sequence NH2-(D)Naph-Cys-Tyr-
(D)Trp-Lys-Val-Cys-Thr-CONH2 (BIM 23014C) and its cyclic
derivative of sequence NH2-(D)Naph-Cys-Tyr-(D)Phe-Lys-Val-
Cys-Thr-CONH2 (BIM 23A462C) were obtained from Ipsen
Pharma (Barcelona) as acetate salts (molecular masses of 1,095
and 1,060 Da, respectively, purity ?98%). Mixtures were made
by dissolving the peptides powders at 10–14% wt?wt in pure
water. Glycerol (99.9%) was purchased from Sigma.
Optical Microscopy. Very thin preparations between glass slides
were observed with a Nikon microscope equipped with two
crossed polarizers. A color plate was used to analyze the
deformation orientations.
Electron Microscopy. Electron microscopy observations were pre-
ceded by freeze-fracture and freeze-etching of samples contain-
ing 30% wt?wt dried glycerol as cryoprotectant. Small aliquots
of the samples were placed on copper grids, frozen in liquid
propane, and stored in liquid nitrogen. Freeze-fracture, freeze-
etching, and replication were successively performed by using a
Balzers 301 apparatus equipped with an electron gun for plat-
inum shadowing. Replicates were examined by using a Philips
301 electron microscope.
SAXS. X-ray diffraction experiments were performed at the High
Brilliance beam line (ID2), European Synchrotron Radiation
Facility in Grenoble, France (13). The undulator x-ray beam (of
wavelength 0.99 Å) was selected by a channel-cut Si(111) crystal,
and focused by rhodium-coated toroidal mirror. The beam size
defined by the collimating slits was 0.2 mm ? 0.2 mm. The
detectorwasanimageintensifiedcharge-coupleddevicecamera,
and the sample-to-detector distance varied between 150 and
650 cm.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: SAXS, small angle x-ray scattering; WAXS, wide angle x-ray scattering.
§M.P. and F.A. contributed equally to the work.
‡‡To whom correspondence should be addressed. E-mail: franck.artzner@cep.u-psud.fr.
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X-Ray Fiber Diffraction and Analysis. The setup was the same as in
SAXS, with a sample-detector distance of 90 cm. In addition,
high-resolution x-ray patterns were collected with a 45 ? 36-cm2
image-plate detector at a distance of 65 cm. Theoretically, the
fiber diffraction pattern (14) is horizontal layer lines localized in
the reciprocal space at qz? lc* and whose intensity Il(qr) is
Il?qr? ? ??Fl?qr, ?, lc*???2,
[1]
where ?, qr, and qzare the angular, radial, and axial cylindrical
coordinates of the reciprocal space, and with
Fl?qr, ?, lc*? ? ?
n???
2??
??
Fnl?qr?exp?in??
[2]
Fnl?qr? ? exp?in?
0
?
?nl?r?Jn?2?r?2?r dr,
[3]
where Jnis the Bessel function of order n and
2??
00
?nl?r? ?
1
2??
c
?M?r, ?, z?exp??i?n? ?2?lz
c??dr d?,
[4]
where ?M(r, ?, z) is the electron density of the tube function in
cylindrical coordinate ?, r, and z. In the case of a thin cylinder
of radius r0, the diffuse scattering is reduced to horizontal lines
with intensity profiles I(qr.r0). For peaks corresponding to q ?
h.i* ? k.j*, with i* and j* the reciprocal vectors of the (i, j)
lattice, the profile is a Bessel function of order l ? h.n ? k.m, i.e.,
I(qr.r0) ? [Jl(qr.r0)?qr.r0]2, and the vertical position is qz ?
h.iz* ? k.jz*.
Fourier-Transform Raman Spectroscopy. Spectra were recorded at 4
cm?1resolutionbyusingaBrukerIFS66interferometercoupled
to a Bruker FRA 106 Raman module equipped with a contin-
uous Nd:YAG laser providing excitation at 1,064 nm. All spectra
were recorded at room temperature with backscattering geom-
etry from concentrated samples held in standard aluminum
cups. The spectra obtained resulted from 5,000 coadded
interferograms.
Fourier-Transform Infrared Spectroscopy. Attenuated total reflec-
tance (ATR) Fourier transform infrared spectra were measured
at a 2-cm?1resolution with a Bruker IFS 66 spectrophotometer
equipped with a 45° N ZnSe ATR attachment. The spectra
obtained resulted from the average of 50 scans and were
corrected for the linear dependence on the wavelength of the
absorption measured by ATR. The water signal was removed by
subtraction of pure water spectrum. Analysis of the conforma-
tions of the peptides was performed by deconvolution of the
absorption spectra as a sum of Gaussian components.
Results
Nanotube Morphology and Organization.Lanreotideacetateandits
derivative spontaneously form gels in water at 10% (wt?wt)
concentration. Optical textures observed between crossed po-
larizers (Fig. 1) are developable surfaces, which are compatible
with a columnar hexagonal liquid-crystal phase. Electron mi-
crographs of freeze-etching replicates show tightly packed long
and thin nanotubes (Fig. 2 a and b). In the case of Lanreotide,
SAXS experiments reveal that these nanotubes have a 2D
hexagonal packing with a lattice parameter (ahex) of 365 Å, a
monodisperse diameter (?) of 244 Å and a wall thickness (e) of
?18 Å (Fig. 2 c and d). Moreover, the absence of order along the
direction of the tubes axis demonstrates that the nanotubes
freely slide in a hexagonal liquid crystalline phase (15, 16).
Lanreotide Conformation. FT-Raman spectroscopy shows the
presence of a disulfide bridge in the Lanreotide structure, with
a gauche–gauche–gauche conformation as evidenced by the
presence of the characteristic 506-cm?1vibration (Fig. 3a) (17).
The amide I vibrations observed by Fourier transform infrared
spectroscopy indicate that 35% of the hydrogen bonds implying
backbone carbonyl groups are involved in antiparallel ?-sheet,
15% in turn and 50% in random conformations (Fig. 3b) (18).
These data strongly support a planar ?-hairpin conformation for
the peptide backbone with a turn located at the D-tryptophan
residue, which is stabilized by the disulfide bridge and intramo-
lecular hydrogen bonds. This conformation enhances the am-
phiphilic nature of the peptide by exposing the hydrophilic
disulfide bridge on one face of the ?-hairpin, whereas the
hydrophobic residues are exposed on the other face. Further-
more, the aromatic residues are segregated from the aliphatic
ones, each being located on one ?-strand. Given the ?-hairpin
conformation, three couples of hydrogen bond donors?
acceptors are in the right orientation to form a ?-sheet fiber.
Fiber Diffraction. The organization within the nanotube wall is
crystalline as shown by an exceptionally well aligned WAXS
pattern (mosaicity ?0.5°) acquired with the Lanreotide deriva-
tive (Fig. 4a). This diffraction pattern can be unambiguously
interpreted in terms of a 2D curved crystal (further analysis
reveals the formation of ripples along the i vector constituted by
two filaments). The position of diffuse scattering maxima can be
indexed by a 2D monoclinic lattice i ? 20.7 Å, j ? 20.8 Å, ? ?
117.2°, with j at an angle of 48.3° with respect to the direction of
the cylinder axis. The line shapes of the diffuse scattering can be
simulated (Fig. 4 b and c) by Bessel functions corresponding to
the Fourier transform of a 2D lattice (Fig. 4d). The molecular
organization of both Lanreotide and its derivative are identical
as indicated by the similarity of all of the cell parameters (Table
1). In both cases, the Patterson function of the nanotube walls,
calculated from the main diffuse scattering, reveals a 20.8 Å
alternation of low and high electron density along the j vector
Fig. 1.
b) and its derivative (c and d) observed between cross-polarizers (?45°)
through thin preparations (magnification, ?2,500). A color plate is added in
b. (c) Texture growing from isotropic liquid (magnification, ?1,250). The
observedfan-shapetexturesarecharacteristicdeformationsofparallelplanes
in developable surfaces (arrows). These deformations are compatible with
hexagonal columnar liquid-crystal phases (or lamellar phases).
Optical textures of hexagonal columnar phases of Lanreotide (a and
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(Fig. 4e), i.e., a segregation between aromatic?aliphatic residues.
A ?-sheet stacking made by a unique peptide translation leads
to a repeat distance of ?9.4 Å (2 ? 4.7 Å) and is not in
agreement with the experimental one of 20.8 Å. Moreover,
such a stacking would not create the aromatic?aliphatic alter-
nation. On the contrary, ?-sheet fibers built from an alternated
stacking of antiparallel peptides (Fig. 4e) would be in agree-
ment with both observed repeat distance and aromatic?
aliphatic segregation.
Structural Model of Nanotube Wall. The surface S per unit cell is
380 Å2and contains two molecules. If we assume that, as for
proteins, the Lanreotide density ranges from 1.2 to 1.3, then the
volume V of the molecule can be estimated to be 1,400–1,500 Å3.
The thickness t of one fiber estimated by using t ? 2.V?S ranges
between 7.4 and 8 Å, which is about half the wall thickness of the
nanotubes (18 Å). Therefore, two superimposed ?-sheet fibers
constitute a single filament, which is visualized on the Patterson
Fig. 2.
electron micrographs of a 14% wt?wt Lanreotide acetate–water sample. The
planes of fracture are perpendicular (a) and parallel (b) to the director of the
tightly packed thin tubes. (Insets) A ?2 enlargement of the corresponding
micrographs. (c) SAXS with sample–detector distance of 6 m. Superimposed
lines indicate calculated values in the case of a 2D columnar hexagonal phase
with a packing parameter ahexof 365 Å, which corresponds to the distance
between the centers of the nanotubes. (d) SAXS with a sample–detector
distance of 1.5 m. The diffraction peaks are not resolved, but their envelope
(form factor) is observed. The zeros are in agreement with a Bessel function
(J0(q?r0)?q?r0)2(dashed curve), which corresponds to the form factor of a
monodisperse cylinder of radius r0? 122 Å. The wall thickness of the nano-
tubes, estimated from the position of the last oscillation, is ?18 Å.
Characterization of Lanreotide nanotubes. (a and b) Freeze-fracture
Fig. 3.
tional spectroscopies. (a) Fourier transform (FT)–Raman spectroscopy. The
figure shows the frequency range of disulfide bond vibrations. The 506-cm?1
vibration (arrow) indicates a gauche–gauche–gauche disulfide bridge. The
519-cm?1vibration is characteristic of the Naphthalene ring of the D-
naphthylalanineresidue.(b)Fouriertransforminfraredspectrumoftheamide
I region (vibrations of the carbonyl groups) after subtraction of the water
contribution. The percentages of backbone carbonyls involved in hydrogen
bonds in different conformations have been estimated after deconvolution,
i.e., 35% of antiparallel ?-sheet (1,618 and 1,689 cm?1), 15% of turn (1,663
cm?1), and 50% of random (1,639 cm?1).
Conformation of Lanreotide in the nanotubes determined by vibra-
Fig. 4.
resolution fiber diffraction of the Lanreotide derivative at 10% wt?wt (ace-
tate) in water. (b and c) Simulations of diffuse scattering at wide angles
(WAXS) of selected zones (rectangles in a). (d) Two-dimensional Patterson
functionindicatingthemainelectrondensityvariationsofthenanotubewall.
(e) Zoom of the unit cell and definition of the cell vectors i and j. The black
circles indicate the 2-fold symmetry axes. The ?-hairpin backbone of Lan-
reotide is drawn on the zoom to fit the regions of high (red) and low (blue)
electrondensities.Notethealternationoflowandhighelectrondensityareas
along j and the continuity of these areas along i.
Crystalline structure of the wall of Lanreotide nanotubes. (a) High-
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function (Fig. 4d). Thus, the amphiphilic nature of the peptide
induces the formation of a bilayer (Fig. 5 a and b), in which the
confined hydrophobic residues are protected from water by the
inner and the outer ?-sheet fibers and by the hydrophilic
residues.
Four fiber organizations within the filament are in agreement
with the alternation of aliphatic and aromatic residues. All of
them are constituted by two molecules related by a 2-fold axis.
The first two fiber organizations (Fig. 7, which is published as
supporting information on the PNAS web site, www.pnas.org)
would exhibit a repeat distance equal to four times the hydrogen
bondrepeatdistanceofa?-sheet(4.75Å),i.e.,19.0Å.Thesetwo
fiber possibilities are in contradiction with the experimental
repeat distances (20.8 Å for Lanreotide and 21.1 Å for its
derivative) and, consequently, the fiber solution is among the
two other ones. The two remaining solutions (Fig. 5b) would
exhibit a repeat distance of [(4*4.75)2? 72]1/2? 20.2 Å, in which
the 7 Å represents the length of a shift of one residue along the
peptide backbone. Because a filament is constituted by two
amphiphilic ?-sheet fibers and because a bilayer formed by two
identical organizations cannot be spontaneously curved, the
organization of the inner and the outer ?-sheet fibers has to be
different. At the molecular level, the two remaining ?-sheet
organizations only differ in the nature of the amino acids
involved in the intermolecular hydrogen bonds. The stacking of
these two different ?-sheets, described in Fig. 5b, exhibit 2-fold
axes that would meet exactly when aromatic residues interact in
a Naph?Tyr?Tyr?Naph sequence. Therefore, we proposed that
thefilamentsareconstitutedbytheassociationofthesetwotypes
of fibers.
Considering this structural model of the filaments, the nano-
tubes would be formed by the self-assembly of 26 identical
filaments of Lanreotide (18 identical filaments for the deriva-
tive) resulting in the high monodispersity of the nanotube
diameter (Fig. 5c and Table 1). Furthermore, fiber diffraction
pattern indicates that these filaments coil up around the tube at
an angle of 48.5° with respect to the direction of the cylinder axis.
Considering this filament orientation, the model gives a hydro-
gen bond orientation of 29° with respect to the direction of the
cylinder axis.
Discussion
Interactions Driving Nanotube Formation. The structure of Lan-
reotide nanotubes in water reveals the interactions responsible
for the self-assembly. Along the three directions of the nanotube
wall crystal, the driving forces are the hydrophobic effect
generating a bilayer of fibers forming the filament (Fig. 5 a and
b), the hydrogen-bond network maintaining the filament struc-
ture along the j vector (Fig. 5b), and the hydrophobic effect again
stabilizing the lateral packing of 26 filaments along the i vector
(Fig. 5c). In addition, the whole structure highlights a systematic
segregation of aromatic from aliphatic residues. Indeed, fila-
ments exhibit a rigorous and systematic alternation of aromatic
and aliphatic regions along the hydrogen bonds direction (j) and
within the bilayers of fibers (Fig. 5b). Moreover, the Patterson
electron density map (Fig. 4e) shows that interactions between
filaments lead to the formation of continuous regions of either
Table 1. Nanotube parameters
ahex, Å
?, Å
d, Å i (n), Åj (m), Å
?, °
S, Å2
Lanreotide
Derivative
365
259
244
166
243
176
20.7 (13)
20.2 (11)
20.8 (26)
21.1 (18)
119.0
117.2
377
380
Supramolecular and molecular parameters of the nanotubes formed by
Lanreotide and its derivative in water. Supramolecular parameter: ahexis the
hexagonal parameter (Fig. 5d) obtained by SAXS (Fig. 2c), ? is the diameter of
the nanotubes (Fig. 5c) from SAXS (Fig. 2d), and d ? ahex? ??2 (see text).
Molecular parameter calculated from the fiber diffraction X-ray pattern (Fig.
4 and Fig. 6, which is published as supporting information on the PNAS web
site, www.pnas.org): i and j are the unit-cell vectors of the bidimensional
curved crystal (Fig. 4e), ? is the (i, j) angle, and S is the surface of the unit cell.
n and m are the number of filaments whose direction is along i and j,
respectively, constituting a nanotube.
Fig.5.
of Lanreotide-acetate nanotubes in water. (a) (Left) The Lanreotide molecule
in the ?-hairpin planar conformation, which is stabilized by the disulfide
bridge, the turn, and intramolecular hydrogen bonds. (Right) Interaction
betweentwoLanreotidemoleculeswithinthewall(bilayer)ofthenanotubes.
(Bottom) CPK models of a conformation in agreement with experimental
data.Thesegregationofaromaticresidues(red)fromaliphaticresidues(blue)
and from hydrophilic region (green) is remarkable. (b) The structure of a
filament with two different ?-sheet fibers superimposed with their C22-fold
axes (black circles) meeting together. The segregation between aliphatic?
aromatic residues is conserved within the filament organization. (Inset) Pack-
ing of the aromatic residues within the ?-sheet fibers. (c) Self-assembly of 26
filamentstoformananotube.(d)Liquidcrystallinehexagonalcolumnarphase
formed by the nanotubes.
Schematicviewofthedifferenthierarchicallevelsintheself-assembly
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aliphatic or aromatic residues along the i vector. This feature
essentially results from the constraints exerted by the disulfide
bridge and intramolecular interactions on the Lanreotide back-
bone. Indeed, the resulting ?-hairpin conformation enhances the
initial segregation present in the peptide sequence.
Implication for ?-Sheet Fibrils. E. Gazit (19) recently pointed out
the importance of aromatic ?-stacking in the self-assembly
process leading to amyloid fibrils. This analysis was essentially
based on the statistics of aromatic residues occurring in amyloid-
related sequences. Similarly, in the two ?-strands of the native
PrP human prion protein, responsible for the Creutzfeld–Jakob
disease (20), three residues among the eight hydrophobic ones
are aromatic (tyrosine), suggesting the involvement of aromatic
residues in the conformation change of the prion protein. Here
we show that aromatic residues are segregated from aliphatic
residues in all of the hierarchical levels of the supramolecular
organization of Lanreotide nanotubes. Therefore, we propose
that the aliphatic?aromatic segregation plays a significant role in
the conversion to ?-sheet fibrils.
The importance of the peptide charge in the formation of
fibrils has been reported (21, 22). Fibrils formation does not
occur (i) if the peptide charge is vanishing because of precipi-
tation or (ii) when the effective charge is too high and inhibits
the fiber formation by electrostatic repulsion. In the case of
Lanreotide, the effective charge is of ?2. A filament in a
nanotube is under two electrostatic repulsion forces, one coming
from the neighbor filaments in the same nanotube and the other
coming from the neighbor nanotubes. The former repulsion
tends to increase the size of the nanotube, whereas the latter
tends to make it decrease. The electrostatic field generated by
the neighbor filaments can be approximated by ??2? with ? the
surfacechargeofthewalland?thedielectricpermitivity.Forthe
neighbor nanotubes, the electrostatic field can be estimated in
first approximation by ?.??2?d, with ? being the nanotube
diameter and d being the distance between the considered
filament and the center of the neighbor nanotube. The filament
would be at mechanical equilibrium when both electric fields are
balanced, i.e., when d is ??. This means that the mechanical
equilibrium would be reached when the distance between the
nanotubes is about their radius (122 Å for Lanreotide and 83 Å
for its derivative). The experimental data, for both Lanreotide
and derivative, are in agreement with this simple model (Table
1) and suggest that electrostatic forces play a major role in the
formation of nanotubes in the hexagonal lattice.
The supramolecular organization of Lanreotide reported here
demonstrates that this system is able to investigate the minimal
interactions required for generating large self-assembling nano-
tubes already observed with proteins (23–26) or lipids (27, 28).
Furthermore,thepotentialapplicationsofthistypeofnanotubes
include nanofiltration of biological molecules (29) and templates
to fabricate ordered mesoporous materials (1). Currently, a
Lanreotide acetate hydrogel of higher concentration than the
one studied here is used as a therapeutic in the treatment of
acromegaly in the form of a long-acting s.c. implant (Autogel)
(12). The exceptional self-assembling properties of Lanreotide
acetate in water suggest a correlation between Lanreotide
nanotube organization and the controlled release properties of
this pharmaceutical product.
We are grateful to Dr. Dominique Durand for the high quality of her
support during preliminary experiments performed on D43 at LURE
synchrotron. This work was supported by Centre National de la Recher-
che Scientifique (AC Nanosciences-Nanotechnologies), Universite ´ Paris
XI, and by a Beaufour–Ipsen?Centre National de la Recherche Scien-
tifique grant (to C.V.). European Synchrotron Radiation Facility is
acknowledged for provision of beam time (SC801).
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