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Self-assembly of giant peptide nanobelts.

ABSTRACT: Many alkylated peptide amphiphiles have been reported to self-assemble into cylindrical nanofibers with diameters on the order of a few nanometers and micrometer scale lengths; these nanostructures can be highly bioactive and are of great interest in many biomedical applications. We have discovered the sequences for these molecules that can eliminate all curvature from the nanostructures they form in water and generate completely flat nanobelts with giant dimensions relative to previously reported systems. The nanobelts have fairly monodisperse widths on the order of 150 nm and lengths of up to 0.1 mm. The sequences have an alternating sequence with hydrophobic and hydrophilic side chains and variations in monomer concentration generate a "broom" morphology with twisted ribbons that reveals the mechanism through which giant nanobelts form. Interestingly, a variation in pH generates reversibly periodic 2 nm grooves on the surfaces of the nanobelts. With proper functionalization, these nanostructures offer a novel architecture to present epitopes to cells for therapeutic applications.

SUBMITTER: Cui H

PROVIDER: S-EPMC2669492 | biostudies-literature | 2009 Mar

REPOSITORIES: biostudies-literature

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Self-assembly of giant peptide nanobelts.

Cui Honggang H Muraoka Takahiro T Cheetham Andrew G AG Stupp Samuel I SI

Nano letters 20090301 3

Many alkylated peptide amphiphiles have been reported to self-assemble into cylindrical nanofibers with diameters on the order of a few nanometers and micrometer scale lengths; these nanostructures can be highly bioactive and are of great interest in many biomedical applications. We have discovered the sequences for these molecules that can eliminate all curvature from the nanostructures they form in water and generate completely flat nanobelts with giant dimensions relative to previously report ...[more]

PMID: 19193022

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Project description:The characterization of self-assembling molecules presents significant experimental challenges, especially when associated with phase separation or precipitation. Transparent window infrared (IR) spectroscopy leverages site-specific probes that absorb in the "transparent window" region of the biomolecular IR spectrum. Carbon-deuterium (C-D) bonds are especially compelling transparent window probes since they are non-perturbative, can be readily introduced site selectively into peptides and proteins, and their stretch frequencies are sensitive to changes in the local molecular environment. Importantly, IR spectroscopy can be applied to a wide range of molecular samples regardless of solubility or physical state, making it an ideal technique for addressing the solubility challenges presented by self-assembling molecules. Here, we present the first continuous observation of transparent window probes following stopped-flow initiation. To demonstrate utility in a self-assembling system, we selected the MAX1 peptide hydrogel, a biocompatible material that has significant promise for use in drug delivery and medical applications. C-D labeled valine was synthetically introduced into five distinct positions of the twenty-residue MAX1 β-hairpin peptide. Consistent with current structural models, steady-state IR absorption frequencies and linewidths of C-D bonds at all labeled positions indicate that these side chains occupy a hydrophobic region of the hydrogel and that the motion of side chains located in the middle of the hairpin is more restricted than those located on the hairpin ends. Following a rapid change in ionic strength to initiate self-assembly, the peptide absorption spectra were monitored as function of time, allowing determination of site-specific time constants. We find that within the experimental resolution, MAX1 self-assembly occurs as a cooperative process. These studies suggest that stopped-flow transparent window FTIR can be extended to other time-resolved applications, such as protein folding and enzyme kinetics.

Project description:BackgroundDue to their natural tendency to self-assemble, proteins and peptides are important components for organic nanotechnology. One particular class of peptides of recent interest is those that form amyloid fibrils, as this self-assembly results in extremely strong, stable quasi-one-dimensional structures which can be used to organise a wide range of cargo species including proteins and oligonucleotides. However, assembly of peptides already conjugated to proteins is limited to cargo species that do not interfere sterically with the assembly process or misfold under the harsh conditions often used for assembly. Therefore, a general method is needed to conjugate proteins and other molecules to amyloid fibrils after the fibrils have self-assembled.ResultsHere we have designed an amyloidogenic peptide based on the TTR105-115 fragment of transthyretin to form fibrils that display an alkyne functionality, important for bioorthogonal chemical reactions, on their surface. The fibrils were formed and reacted both with an azide-containing amino acid and with an azide-functionalised dye by the Huisgen cycloaddition, one of the class of "click" reactions. Mass spectrometry and total internal reflection fluorescence optical microscopy were used to show that peptides incorporated into the fibrils reacted with the azide while maintaining the structure of the fibril. These click-functionalised amyloid fibrils have a variety of potential uses in materials and as scaffolds for bionanotechnology.DiscussionAlthough previous studies have produced peptides that can both form amyloid fibrils and undergo "click"-type reactions, this is the first example of amyloid fibrils that can undergo such a reaction after they have been formed. Our approach has the advantage that self-assembly takes place before click functionalization rather than pre-functionalised building blocks self-assembling. Therefore, the molecules used to functionalise the fibril do not themselves have to be exposed to harsh, amyloid-forming conditions. This means that a wider range of proteins can be used as ligands in this process. For instance, the fibrils can be functionalised with a green fluorescent protein that retains its fluorescence after it is attached to the fibrils, whereas this protein loses its fluorescence if it is exposed to the conditions used for aggregation.

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Self-assembly of giant peptide nanobelts.

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Self-assembly of giant peptide nanobelts.

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