Propensity of self-assembling



peptides has the propensity of self-assembling, as the concentration of peptides increases in the solution, the monomers interact with each other via intermolecular hydrogen bonding to form β-sheet tapes and ribbons which, at certain concentration forms entangled gel networks. These tapes and ribbons stack together to form nanofibrils which, at certain concentration forms nematic gels. This self-assembly process is driven by van der Waal forces, weak noncovalent interactions, hydrogen bonding, electrostatic interactions, stacking effects and hydrophobicity.  The ability of β-sheet peptides to self assemble into well defined nanostructures makes these interesting into nano-engineered projects. Here we explore the properties and applications of these well defined nano structures.

The properties of peptide based self assembled nanostructures can be engineered by designing an appropriate peptide to match the criteria of the specific application.


Tape is the simplest form of polymer made of β-sheet self-assembly. Here we are investigating the β-sheets tapes formed by a 24-reside peptide K-24, with primary structure (NH2-Lys-Leu-Glu-Ala-Leu-Tyr-Val-Leu-Gly-Phe-Phe-Gly-Phe-Thr-Leu-Gly-Ile-Arg-COOH). K24 peptides form β-sheet tapes in amphiphilic solvents such as methanol or 2-chloroethanol, transparent viscoelastic gels are formed at concentrations above 0.002 volume fraction (~3mg m/l), of ~8nm wide and 0.1µm length with a 4.7 Ao structural periodicity. These tapes are twisted due to the intrinsic chirality of the peptides [1]. It has a left handed twist around the long axis of the tape which stems from the chirality of the monomers. Tapes have two distinct faces, which are chemically different i.e., one face of the tape is less soluble than the other. Their affinity to the solvent and difference in the chemical structure give rise to a cylindrical curvature which causes the tape to curl into helical configuration. [2] Further information of the gel structure is given by rheological properties. These gels are optically isotropic, and when sheared it becomes optically birefringment. The response to the stress is seen to be linear up to strains of 230%. Viscosity of the gel depends on the concentration of the peptide i.e. a 0.0011 v/v K24 solution in methanol (1.5 mg m/l) is a fluid whereas a 0.0074 v/v solution in methanol (10 mg m/l) gives a solid like transparent gel.  The chemical stability of the peptide bond and thermostability of the tapes proposes that these polymers are robust. Tapes show similarity, in structural terms to protein fibrils.[3] Persistent lengths, long contour, lateral tape-tape attractions and topological entanglement properties are responsible for the formation of large mesh size at low concentrations of peptide.[4] mechanical properties namely elastic and viscous moduli are comparable with biopolymer gels under linear deformation, but show much greater recoverable strain, which reveals that gels are brittle and stronger than biopolymer gels. Another remarkable property of gels is, they respond to the chemical and physical triggers. Reversibility of gelation is a significant property of the polymer network. These gels are biodegradable and biocompatible.


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Tapes can interact with each other to give rise to more complex polymeric nanostructures. Ribbons are formed due to the chemical anisotropy in the tapes which results in intertape attractions and forms double tape (ribbon). Ribbons have two faces which are identical and are characterized by a saddle curvature.


The physical properties of the peptide materials studied are sensitively related to the charge fraction, the chirality and the interpeptide energy. There is a complicated variety of physical intereactions which occur in self assembling peptides.

Both sides of β-sheet ribbons are same and hence they stack on each other to form fibrils.Here we are investigating the fibrils formed by P11-II with structure (CH3CO-Gln-Gln-Arg-Phe-Gln-Trp-Gln-Phe-Glu-Gln-Gln-NH2)

Fibrils have a well defined screw-like structure with typical minimum and maximum widths. The formation of fibrils at higher concentrations of p11-11 implies the presence of a weaker attraction between the polar sides of p11-11 ribbons. Despite this attraction the fibril dispersions are stable and the fibril diameter is finite. The fibril width corresponds to expected length of an 11 reside b strand and thickness corresponds to roughly 4 ribbons. Fibrils are made typically of 8 ribbons. The energy required to break such fibril is scission energyis higher than a single ribbon. The fibril also exhibit a left had twist with a helix pitch. The fibrils have a persistence length which makes the fibrils considerably more rigid than the ribbons. The expexted persistant length made of p=4 ribbons is upto 64 ribbons higher than the ribbon persistant lenth. The rigidity of the fibrils give rise to the formation of nematic phase. The fibrils behave more like typical semirigid chains with hard core excluded volumes. Rheological measurements show that fibril based gels are brittle and do not relax even after days, behaviour reminiscent of permanent gels of semi rigid polymers. In contrast tape based gels are more extendable and relax slowly with time, behaviour indicative of transient gels of semi flexible polymers. Properties like flexibility, contour length and cross linking mechanism determine the liuid crystalline structure and gealtion properties of the solution.  Fibril formation takes up to several weeks to complete..gelation occurs even more slowly.the extremely slow kinetics originates from the multiplicity of molecular interactions in fibrils.


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Mixing of cationic and anionic solutions forms polyelectrolyte β-sheets which self assembles into fibillar network and produces biodegradable and biocompatible nematic hydrogels which have potential applications in encapsulation, immobilization and separation of cells, enzymes or antibodies, proteins. [9]

One of the potential applications of self assembled peptides is injectable joint lubricants for osteoarthritis (OA). Due to the low viscosity of the peptide solutions delivery of the sample can be done by injection.  These are used as a new viscosupplementation treatment for early stage OA. Basing on the design criteria of Hyaluronic acid (HA) (plays significant role in joint lubrication), a range of de novo peptides are prepared which self assemble into nematic fluids and gels under physiological conditions. Due to the higher scission energy of tapes and ribbons, fibrils are found to be robust as its scission energy is comparable to scission energy of covalent bond. Tape forming peptides are to be designed, because tapes are more flexible than fibrils and hence they are more reminiscent of the properties of HA and also tapes are more effective water binding and lubrication. [10]

Fibrillar scaffolds are used in dental treatment. Peptides are designed to form 3D fibrillar scaffolds in response to external triggers, which can be used in treatment of dental caries and skeletal tissue engineering. P11 -4 changes the de and remineralization behaviour of caries-like lesions under varying pH conditions.  Treatment with P11 -4 solutions resulted in change in net mineral gain by the lesions. This result suggests that self assembling peptides are useful in dental tissue engineering.[11]

Silica nanotubes can be developed by using nanofibrils as a template. Sol-gel condensation of precursor tetraethoxysilane (TEOS) in the presence of positively charged L-P11-3 peptide fibril templates, followed by template extraction results in hollow silica nanotubes. The resulted nanotubes are expected to be chiral and the central pore reflects the dimension of the fibril. Nanotubes with morphologies are produced even before, but by using a template we can prescribe the diameter, pitch, twist and chirality, which provide control of the internal surface architecture. This will result in developing functional materials with prescribed chirality and diameter which has applications in chiral catalysis and separations. [12]

Herewepresentedabioinspiredsilicificationprocessto rapidlyproducewell-definedsilicacompositetapes.For thatself-assembledPEO-peptidenanotapes,exhibiting functionalpatches,wereutilizedtodirectthesilicification process.Inanalogytobiosilicificationprocesses,hydro- lyzedalkoxysilanespecieswereprovided,directlyassilica precursor.Arapidenrichmentoftheprecursoronthe functionalnanotapescontrolsthesilicicacid,preventing uncontrolled3-Dcondensationanddirectingthesilica networkformation.Thus,verylowconcentrationsofsilicic acid(270106

M)andshortreactiontimes(10s)are sufficienttoformwell-definedsilicananocompositetapes. Thesecouldbepotentiallyusedasbuildingblocksforthe bottom-upconstructionofdirectionalscaffoldsoras precursorsforanisotropicsilicatapeswithmesoand microporosity.

By using self-assembledPEO-peptidenanotapesasanink todrawthecompositefibers,themacroscopicformofthefibernetworks,thelinewidth,and bothnetworkorientationaswellasnetworkanisotropycanbedefined.Theplottingprocess reliesonabiomimeticsilicificationroute,whichcombinesself-assemblyandpeptide-directed silicificationinacooperativemanner.Thelocalinjectionof PEO-peptidenanotapesintoathinlayerofadilutesolution ofpre-hydrolyzedTMOSleadstotherapidformationofthe compositefibers,whichexhibitseverallevelsofhierarch- icalorder.

Freeze drying of peptide hydrogels proved am ore efficient method of removing the solvent without destroying the self assembled fibrillar network, leading to a microscopic, aligned lamellar structure consisting of thousands of stacked peptide nanofibrils. These chiral , nanostructured ,low density aerogels are characterized by chemical versatility and regular display of functional groups on their surface.[peptide aerogels]

Control over the process of self assembly is crucial to the design of peptide sustems that assemble and disaasemble with physicochemical cues, including pH, light, ionic strength, temperature and concentration,. pH switiching for example is a relatively simple approach for controlling self assembly. An example is b-peptide p11-4 which is ph sensitive due to the ionisable glutamate and arginine side chains. At concentration below <10 mg/ml it is soluble at neutral ph but adopts a hydrogel state at low ph by self assembly of anti paralle b-sheet tapes which then stack together to form fibrils. It will also form a hydrogel state above critical concentration at ph 7.4 and salt concentration 140mm in cell culture medium with applications including enamel remineralization, injectable scaffolds and joint lubricants.[bio materials for self assembly]


Peptides have an intrinsic propensity for self assembly. Learing to control it can lead to a wealth of versatile peptide based self assembled nanoistructures whose properties can be engineered by appropriate peptide design to match the requirements of specific applications. At high enough concentration in solution these aggregates give rise to organogels, hydrogels or nematic fluids and gels.[dynamic modes fibrils]