Cyclotriveratrylene (CTV) as a new chiral triacid scaffold capable of inducing triple helix formation of collagen peptides containing either a native sequence or Pro-Hyp-Gly repeats

A new triacid scaffold is described based on the cone-shaped cyclotriveratrylene (CTV) molecule that facilitates the triple helical folding of peptides containing either a unique blood platelet binding collagen sequence or collagen peptides composed of Pro-Hyp-Gly repeats. The latter were synthesized by segment condensation using Fmoc-Pro-Hyp-Gly-OH. Peptides were coupled to this CTV scaffold and also coupled to the Kemp's triacid (KTA) scaffold. After assembly of peptide H-Gly-[Pro-Hyp-Gly]2-Phe-Hyp-Gly-Glu(OAll)-Arg-Gly-Val-Glu (OAll)-Gly-[Pro-Hyp-Gly]2-NH2 (13) by an orthogonal synthesis strategy to both triacid scaffolds, followed by deprotection of the allyl groups, the molecular constructs spontaneously folded into a triple helical structure. In contrast, the non-assembled peptides did not. The melting temperature (Tm) of (+/-) CTV[CH2C(O)N(H)Gly-[Pro-Hyp-Gly]2-Phe-Hyp-Gly-Glu-Arg-Gly-Val-Glu-Gly- [Pro-Hyp-Gly]2-NH2]3 (14) is 19 degrees C, whereas KTA[Gly-Gly-[Pro-Hyp-Gly]2-Phe-Hyp-Gly-Glu-Arg-Gly-Val-Glu-Gly- [Pro-Hyp-Gly]2-NH2]3 (15) has a Tm of 20 degrees C. Thus, it was shown for the first time that scaffolds were also effective in stabilizing the triple helix of native collagen sequences. The different stabilizing properties of the two CTV enantiomers could be measured after coupling of racemic CTV triacid to the collagen peptide, and subsequent chromatographic separation of the diastereomers. After assembly of the two chiral CTV scaffolds to the model peptide H-Gly-Gly-(Pro-Hyp-Gly)5-NH2 (24), the (+)-enantiomer of CTV 28b was found to serve as a better triple helix-inducing scaffold than the (-)-enantiomer 28a. In addition to an effect of the chirality of the CTV scaffold, a certain degree of flexibility between the CTV cone and the folded peptide was also shown to be of importance. Restricting the flexibility from two to one glycine residues resulted in a significant difference between the two collagen mimics 20a and 20b, whereas the difference was only slight when two glycine residues were present between the CTV scaffold and the peptide sequence in collagen mimics 30a and 30b.     

The role of cystine knots in collagen folding and stability,part I. Conformational properties of (Pro-Hyp-Gly)5 and (Pro-(4S)-FPro-Gly)5 model trimers with an artificial cystine knot

In analogy to the cystine knots present in natural collagens, a simplified disulfide cross-link was used to analyse the conformational effects of a C-terminal artificial cystine knot on the folding of collagenous peptides consisting of solely (Pro-Hyp-Gly) repeating units. Assembly of the alpha chains into a heterotrimer by previously applied regioselective disulfide-bridging strategies failed because of the high tendency of (Pro-Hyp-Gly)(5) peptides to self-associate and form homotrimers. Only when side-chain-protected peptides were used, for example in the Hyp(tBu) form, and a new protection scheme was adopted, selective interchain-disulfide cross-linking into the heterotrimer in organic solvents was successful. This unexpected strong effect of the conformational properties on the efficiency of well-established reactions was further supported by replacing the Hyp residues with (4S)-fluoroproline, which is known to destabilise triple-helical structures. With the related [Pro-(4S)-FPro-Gly](5) peptides, assembly of the heterotrimer in aqueous solution proceeded in a satisfactory manner. Both the intermediates and the final fluorinated heterotrimer are fully unfolded in aqueous solution even at 4 degrees C. Conversely, the disulfide-crossbridged (Pro-Hyp-Gly)(5) heterotrimer forms a very stable triple helix. The observation that thermal unfolding leads to scrambling of the disulfide bridges was unexpected. Although NMR experiments support an extension of the triple helix into the cystine knot, thermolysis is not associated with the unfolding process. In fact, the unstructured fluorinated trimer undergoes an equally facile thermodegradation associated with the intrinsic tendency of unsymmetrical disulfides to disproportionate into symmetrical disulfides under favourable conditions. The experimental results obtained with the model peptides fully support the role of triple-helix nucleation and stabilisation by the artificial cystine knot as previously suggested for the natural cystine knots in collagens.     

Rational design of single-composition ABC collagen heterotrimers

Design of heterotrimeric ABC collagen triple helices is challenging due to the large number of competing species that may be formed. Given the required one amino acid stagger between adjacent peptide strands in this fold, a ternary mixture of peptides can form as many as 27 triple helices with unique composition or register. Previously we have demonstrated that electrostatic interactions can be used to bias the helix population toward a desired target. However, homotrimeric assemblies have always remained the most thermally stable species in solution and therefore comprised a significant component of the peptide mixture. In this work we incorporate complementary modifications to this triple-helical design strategy to destabilize an undesirable competing state while compensating for this destabilization in the desired ABC composition. The result of these modifications is a new ABC triple-helical system with high thermal stability and control over composition, as observed by NMR. An additional set of modifications, which exchanges aspartate for glutamate, results in an overall lowering of stability of the ABC triple helix yet shows further improvement in the system's specificity. This rationally designed system helps to elucidate the rules governing the self-assembly of synthetic collagen triple helices and sheds light on the biological mechanisms of collagen assembly.     

Triple-helix propensity of hydroxyproline and fluoroproline: comparison of host-guest and repeating tripeptide collagen models

Peptide models have proved important in defining the structural features of the collagen triple-helix. Some models are based on multiple repeats of a given tripeptide unit, while a host-guest design includes an individual tripeptide unit substituted within a constant repeating Pro-Hyp-Gly framework. In the present study, proline, hydroxyproline, and fluoroproline residues are incorporated in X- or Y-positions of a guest triplet in the host-guest peptide design. All host-guest peptides, including Hyp-Pro-Gly, formed stable triple-helices, even though a triple-helix cannot be formed by (Hyp-Pro-Gly)10. The order of stability Pro-Hyp-Gly > Pro-Pro-Gly > Hyp-Pro-Gly remains the same in all models, while the Pro-Flp-Gly is very stabilizing in a repeating context but destabilizing in a host-guest context. The range of thermal stabilities and calorimetric enthalpies is very small among the five host-guest peptides, consistent with the concept that the effect of one Xaa-Yaa-Gly tripeptide unit in the host-guest system would be less than the much larger variations when there are 10 repeating units. However, a simple additive model based on host-guest peptides predicts a greater stability than experimentally observed. The difference in stability contributions of the same tripeptide unit in host-guest versus repeating tripeptide systems illustrates the impact of sequence environment on stability, and factors that play a role include ring puckering as a consequence of electron inductive effects, residual monomer structure, and native state hydration networks.     

Promoting self-assembly of collagen-related peptides into various higher-order structures by metal-histidine coordination

Collagen is an important and widely used biomaterial and therapeutic. The construction of large-scale collagen structures via the self-assembly of small collagen-related peptides has been extensively studied in the past decade. Here, we report a highly effective and simple means to assemble small synthetic collagen-related peptides into various higher-order structures by utilizing metal-histidine coordination. In this work, two short collagen-related peptides in which histidine residues were incorporated as metal binding sites were designed and chemically synthesized: HG(PPG)(9)GH (X9) and HG(PPG)(4)(PHG)(PPG)(4)GH (PHG). Circular dichroism measurements indicated that these two peptides form only marginally stable collagen triple helices but that their stability can be increased upon the addition of metal ions. Dynamic light scattering analyses, turbidity measurements, TEM, and SEM results demonstrated the metal ion-dependent self-assembly of X9 and PHG into supramolecular structures ranging from various nanofibrils to microscale spherical, laminated, and granulated assemblies. The topology and size of these higher-order structures depends both on the metal ion identity and the location of the binding sites. Most intriguingly, the assembled fibrils show similar D-periodicity to that of natural collagen. Our results demonstrate that metal-histidine coordination can serve as an effective force to induce the self-assembly of unstable collagen-related peptides into higher-order structures.     

Reversible Covalent End-Capping of Collagen Model Peptides

The combination of supramolecular aggregation of collagen model peptides with reversible covalent end-capping of the formed triple helix in a single experimental set-up yielded minicollagens, which were characterized by a single melting temperature. In spite of the numerous possible reaction intermediates, a specific synthetic collagen with a leading, middle and trailing strand is formed in a highly cooperative self-assembly process.     

Role of length-dependent stability of collagen-like peptides

Understanding the structure, folding, and stability of collagen is complex because of its length and variations in the amino acid (AA) sequence composition. It is well known that the basic constituent of the collagen helix is the triplet repeating sequence of the form Gly-X(AA)-Y(AA). On the basis of previous models and with the frequency of occurrence of the triplets, the ((Gly-Pro-Hyp)n)3 (where n is the number of triplets) sequence replicate has been chosen as the model for the most stable form of the collagen-like sequence. With a view to understand the role of sequence length (or the number of triplets) on the stability of collagen, molecular dynamics simulations have been carried out by varying the number of triplet units on the model collagen-like peptides. The results reveal that five triplets are required to form the stable triple helix. Further analysis shows that the intermolecular structural rigidity of the imino acid residues, hydrogen bonding, and water structure around the three chains of the triple helix play the dominant roles on its structure, folding, and stabilization.     

Self-assembled heterotrimeric collagen triple helices directed through electrostatic interactions

Collagen, a fibrous protein, is an essential structural component of all connective tissues such as cartilage, bones, ligaments, and skin. Type I collagen, the most abundant form, is a heterotrimer assembled from two identical alpha1 chains and one alpha2 chain. However, most synthetic systems have addressed homotrimeric triple helices. In this paper we examine the stability of several heterotrimeric collagen-like triple helices with an emphasis on electrostatic interactions between peptides. We synthesize seven 30 amino acid peptides with net charges ranging from -10 to +10. These peptides were mixed, and their ability to form heterotrimers was assessed. We successfully show the assembly of five different AAB heterotrimers and one ABC heterotrimer. The results from this study indicate that intermolecular electrostatic interactions can be utilized to direct heterotrimer formation. Furthermore, amino acids with poor stability in collagen triple helices can be "rescued" in heterotrimers containing amino acids with known high triple helical stability. This mechanism allows collagen triple helices to have greater chemical diversity than would otherwise be allowed.     

Collagen-like peptides and peptide–polymer conjugates in the design of assembled materials

Collagen is the most abundant protein in mammals, and there has been long-standing interest in understanding and controlling collagen assembly in the design of new materials. Collagen-like peptides (CLPs), also known as collagen-mimetic peptides (CMPs) or collagen-related peptides (CRPs), have thus been widely used to elucidate collagen triple helix structure as well as to produce higher-order structures that mimic natural collagen fibers. This mini-review provides an overview of recent progress on these topics, in three broad topical areas. The first focuses on reported developments in deciphering the chemical basis for collagen triple helix stabilization, which we review not with the intent of describing the basic structure and biological function of collagen, but to summarize different pathways for designing collagen-like peptides with high thermostability. Various approaches for producing higher-order structures via CLP self-assembly, via various types of intermolecular interaction, are then discussed. Finally, recent developments in a new area, the production of polymer–CLP bioconjugates, are summarized. Biological applications of collagen contained hydrogels are also included in this section. The topics may serve as a guide for the design of collagen-like peptides and their bioconjugates for targeted application in the biomedical arena.     

Positive and negative design leads to compositional control in AAB collagen heterotrimers

Although collagen is the most abundant protein in the human body and has at least 28 types, research involving collagen mimetic systems only recently began to consider the innate ability of collagen to control helix composition and register. Collagen triple helices can be homotrimeric or heterotrimeric, and while some types of natural collagen form only one specific composition of helix, others can form multiple compositions. It is critical to fully understand and, if possible, reproduce the control that native collagen has on helix composition and register. In this Article, we utilize both positive and negative design for the assembly of specific AAB heterotrimers using charged amino acids to form intrahelix electrostatic interactions, which promote heterotrimer formation and simultaneously discourage homotrimers. Homotrimers are further discouraged by reducing hydroxyproline content, which would otherwise lead to nonspecific promotion of triple helix formation. We combine peptides in a 2:1 ratio in which the more abundant peptide has a charge 1/2 and opposite of the less abundant peptide, which can result in the formation of a zwitterionically neutral AAB heterotrimer. Using this approach, we are able to design collagen mimetic systems with full control over the composition of the resulting triple helix. All previous reports on synthetic collagen heterotrimers have shown mixed populations with respect to composition due to varying amounts of residual homotrimers. Our results yield a greater understanding of the self-assembly of collagenous sequences as well as provide a novel design scheme, both positive and negative, for the synthesis of extracellular matrix mimetics.     

Stereoelectronic and steric effects in the collagen triple helix: toward a code for strand association

Collagen is the most abundant protein in animals. The protein consists of a helix of three strands, each with sequence X-Y-Gly. Natural collagen is most stable when X is (2S)-proline (Pro) and Y is (2S,4R)-4-hydroxyproline (4R-Hyp). We had shown previously that triple helices in which X is (2S,4S)-4-fluoroproline (4S-Flp) or Y is (2S,4R)-4-fluoroproline (4R-Flp) display hyperstability. This hyperstability arises from stereoelectronic effects that preorganize the main-chain dihedral angles in the conformation found in the triple helix. Here, we report the synthesis of strands containing both 4S-Flp in the X-position and 4R-Flp in the Y-position. We find that these strands do not form a stable triple helix, presumably because of an unfavorable steric interaction between fluoro groups on adjacent strands. Density functional theory calculations indicate that (2S,3S)-3-fluoroproline (3S-Flp), like 4S-Flp, should preorganize the main chain properly for triple-helix formation but without a steric conflict. Synthetic strands containing 3S-Flp in the X-position and 4R-Flp in the Y-position do form a triple helix. This helix is, however, less stable than one with Pro in the X-position, presumably because of an unfavorable inductive effect that diminishes the strength of the interstrand 3S-FlpC=O...H-NGly hydrogen bond. Thus, other forces can counter the benefits derived from the proper preorganization. Although (Pro-Pro-Gly)7 and (4S-Flp-4R-Flp-Gly)7 do not form stable homotrimeric helices, mixtures of these two peptides form stable heterotrimeric helices containing one (Pro-Pro-Gly)7 strand and two (4S-Flp-4R-Flp-Gly)7 strands. This stoichiometry can be understood by considering the cross sections of the two possible heterotrimeric helices. This unexpected finding portends the development of a "code" for the self-assembly of determinate triple helices from two or three strands.     

The role of cystine knots in collagen folding and stability,part II. Conformational properties of (Pro-Hyp-Gly)n model trimers with N- and C-terminal collagen type III cystine knots

In mature collagen type III the homotrimer is C-terminally cross-linked by an interchain cystine knot consisting of three disulfide bridges of unknown connectivity. This cystine knot with two adjacent cysteine residues on each of the three alpha chains has recently been used for the synthesis and expression of model homotrimers. To investigate the origin of correct interchain cysteine pairings, (Pro-Hyp-Gly)(n) peptides of increasing triplet number and containing the biscysteinyl sequence C- and N-terminally were synthesised. The possibilities were that this origin may be thermodynamically coupled to the formation of the collagen triple helix as happens in the oxidative folding of proteins, or it could represent a post-folding event. Only with five triplets, which is known to represent the minimum number for self-association of collagenous peptides into a triple helix, air-oxidation produces the homotrimer in good yields (70 %), the rest being intrachain oxidised monomers. Increasing the number of triplets has no effect on yield suggesting the formation of kinetically trapped intermediates, which are not reshuffled by the glutathione redox buffer. N-terminal incorporation of the cystine knot is significantly less efficient in the homotrimerisation step and also in terms of triple-helix stabilisation. Compared to an artificial C-terminal cystine knot consisting of two interchain disulfide bridges, the collagen type III cystine knot produces collagenous homotrimers of remarkably high thermostability, although the concentration-independent refolding rates are not affected by the type of disulfide bridging. Since the natural cystine knot allows ready access to homotrimeric collagenous peptides of significantly enhanced triple-helix thermostability it may well represent a promising approach for the preparation of collagen-like innovative biomaterials. Conversely, the more laborious regioselectively formed artificial cystine knot still represents the only synthetic strategy for heterotrimeric collagenous peptides.     

异氰酸苯酯诱导的类胶原多肽自组装

Synthetic matrices provide powerful tools for dissecting molecular interactions involved in the organization of the extracellular matrix (ECM), establishment of cell axis polarity, and suppression of neoplasticity in pre-cancerous endothelial cells. Collagen is the most abundant protein in extracellular matrix. A de novo approach is essential for the synthesis of collagen matrices which can have a broad impact on the understanding of matrix biology and our capacity to construct safe and medically useful biomaterials. Conventionally, the ECM has been studied by an analytical "top-down" approach, where the individual components of the matrix are first isolated and then characterized to explore their biochemical and functional properties. Since native collagen is difficult to modify and can engender pathogenic and immunological side effects, its application on tissue regeneration is limited. Therefore, we attempted to synthesize artificial collagen directly through small organic molecule recognition. The collagen-like peptides possess various benefits such as being clean, programmable, and easy to modify; therefore, in recent years, they have been used as ideal substrates for the synthesis of collagen nanomaterials. The self-assembly of collagen-like peptides is mainly driven by various non-covalent interactions such as electrostatic attraction, π-π stacking, and metal coordination. This renders a difficulty in the rational design of uniform nanostructures from short synthesized peptides and demands a novel strategy. To date, small organic molecules have been rarely used for the self-assembly of collagen-like peptides. In the present study, we attempted to use the small organic molecules for the combined supramolecular self-assembly of collagen-like peptides. Initially, the collagen-like peptides, (POG)₆ and (POG)₈, synthesized by the solid-phase synthesis technique, were both modified chemically using 4, 4'-methylene bis(phenyl isocyanate) to obtain the collagen-like hybrid peptides, AP₆ and AP₈, respectively. Phenyl isocyanate contributes to the formation of potential weak forces, such as hydrogen bonds and π-π stacking at the N-terminal regions of the collagen-like hybrid peptides. The purity and molecular weight of the collagen-like hybrid peptides were analyzed using analytical high-performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization time of flight (MALDI-TOF), respectively. The stability of AP₆ and AP₈ triple helices was analyzed by circular dichroism (CD) spectroscopy. The small organic molecule 4, 4'-methylene bis(phenyl isocyanate) promoted the unfolding of (POG)₆ and increased the melting temperature (T_m) of (POG)₈ from 37.7 to 58.8 ℃to form a triple helix. The hydrodynamic radii of collagen-like hybrid peptides were measured by dynamic light scattering (DLS). Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to analyze the morphology of the aggregation states. AFM results showed that the collagen-like hybrid peptides, AP₆ and AP₈, formed nanofibers spontaneously. Consistent with the AFM results, TEM showed that the AP₆ and AP₈ collagen-like hybrid peptides also formed nanofiber structures. The formation of stable complexes was attributed to the presence of multiple weak interactions such as hydrogen bonding, π-π stacking, and hydrophobic interactions. In the present study, we demonstrated that the chemical modification of collagen-like polypeptides at the N-terminus via the small organic molecule, 4, 4'-methylene bis(phenyl isocyanate), promoted the intramolecular and intermolecular assembly of collagen-like peptides. A simple and effective strategy has been developed in this study to promote the self-assembly of collagen-like peptides.     

Selective covalent capture of collagen triple helices with a minimal protecting group strategy

Collagens and their most characteristic structural unit, the triple helix, play many critical roles in living systems which drive interest in preparing mimics of them. However, application of collagen mimetic helices is limited by poor thermal stability, slow rates of folding and poor equilibrium between monomer and trimer. Covalent capture of the self-assembled triple helix can solve these problems while preserving the native three-dimensional structure critical for biological function. Covalent capture takes advantage of strategically placed lysine and glutamate (or aspartate) residues which form stabilizing charge–pair interactions in the supramolecular helix and can subsequently be converted to isopeptide amide bonds under folded, aqueous conditions. While covalent capture is powerful, charge paired residues are frequently found in natural sequences which must be preserved to maintain biological function. Here we describe a minimal protecting group strategy to allow selective covalent capture of specific charge paired residues which leaves other charged residues unaltered. We investigate a series of side chain protecting groups for lysine and glutamate in model peptides for their ability to be deprotected easily and in high yield while maintaining (1) the solubility of the peptides in water, (2) the self-assembly and stability of the triple helix, and (3) the ability to covalently capture unprotected charge pairs. Optimized conditions are then illustrated in peptides derived from Pulmonary Surfactant protein A (SP-A). These covalently captured SP-A triple helices are found to have dramatically improved rates of folding and thermal stability while maintaining unmodified lysine–glutamate pairs in addition to other unmodified chemical functionality. The approach we illustrate allows for the covalent capture of collagen-like triple helices with virtually any sequence, composition or register. This dramatically broadens the utility of the covalent capture approach to the stabilization of biomimetic triple helices and thus also improves the utility of biomimetic collagens generally.

A minimal protecting group strategy is developed to allow selective covalent capture of collagen-like triple helices. This allows stabilization of this critical fold while preserving charge–pair interactions critical for biological applications.     

2D Crystal Engineering of Nanosheets Assembled from Helical Peptide Building Blocks

The successful integration of 2D nanomaterials into functional devices hinges on developing fabrication methods that afford hierarchical control across length scales of the entire assembly. We demonstrate structural control over a class of crystalline 2D nanosheets assembled from collagen triple helices. By lengthening the triple helix unit through sequential additions of Pro‐Hyp‐Gly triads, we achieved sub‐angstrom tuning over the 2D lattice. These subtle changes influence the overall nanosheet size, which can be adjusted across the mesoscale size regime. The internal structure was observed by cryo‐TEM with direct electron detection, which provides real‐space high‐resolution images, in which individual triple helices comprising the lattice can be clearly discerned. These results establish a general strategy for tuning the structural hierarchy of 2D nanomaterials that employ rigid, cylindrical structural units.     

Metal-mediated tandem coassembly of collagen peptides into banded microstructures

The ability to recapitulate the features of natural collagen at the micro- and nanoscale with novel biopolymers has the potential to lead to improved biomaterials. Herein we describe stimuli-responsive collagen-based peptides (IdaCol and HisCol) that together form higher order assemblies in the presence of added metal ions. SEM and TEM imaging of these assemblies revealed microscale petal-like and intertwined fiber morphologies, each with periodic banding on the nanometer scale. The observed banding is consistent with tandem coassembly of alternating IdaCol and HisCol triple helical blocks that may laterally associate either in or out of register to form higher order structures, and mimics the banding found in natural collagen fibers.     

Computational design of a collagen A:B:C-type heterotrimer

We have successfully designed an A:B:C collagen peptide heterotrimer using an automated computational approach. The algorithm maximizes the energy gap between the target and competing misfolded states while enforcing a minimum target stability. Circular dichroism (CD) measurements confirm that all three peptides are required to form a stable, structured triple helix. This study highlights the power of automated computational design, providing model systems to probe the biophysics of collagen assembly and developing general methods for the design of fibrous proteins.     

Photocontrol of the collagen triple helix: synthesis and conformational characterization of bis-cysteinyl collagenous peptides with an azobenzene clamp

For the photomodulation of the collagen triple helix with an azobenzene clamp, we investigated various collagenous peptides consisting of ideal (Gly-Pro-Hyp) repeats and containing cysteine residues in various positions for a side chain-to-side chain crosslink with a suitable chromophore derivative. Comparative conformational analysis of these cysteine peptides indicated an undecarepeat peptide with two cysteine residues located in the central portion in i and i+7 positions and flanked by (Gly-Pro-Hyp) repeat sequences as the most promising for the cross-bridging experiments. In aqueous alcoholic solution the azobenzene-undecarepeat peptide formed a stable triple helix in equilibrium with the monomeric species as a trans-azobenzene isomer, whereas photoisomerization to the cis isomer leads to unfolding of at least part of the triple helix. Furthermore, the residual supercoiled structure acts like an intermolecular knot, thus making refolding upon cis-to-trans isomerization a concentration-independent fast event. Consequently, these photoswitchable collagenous systems should be well suited for time-resolved studies of folding/unfolding of the collagen triple helix under variable thermodynamic equilibria.     

Peptides that anneal to natural collagen in vitro and ex vivo

Collagen comprises ? of the protein in humans and ? of the dry weight of human skin. Here, we implement recent discoveries about the structure and stability of the collagen triple helix to design new chemical modalities that anchor to natural collagen. The key components are collagen mimetic peptides (CMPs) that are incapable of self-assembly into homotrimeric triple helices, but are able to anneal spontaneously to natural collagen. We show that such CMPs containing 4-fluoroproline residues, in particular, bind tightly to mammalian collagen in vitro and to a mouse wound ex vivo. These synthetic peptides, coupled to dyes or growth factors, could herald a new era in assessing or treating wounds.     

Dielectric assembly of a collagen-model polypeptide in a triple helix

In expectation of the formation of a thermally stable, dielectric supramolecular assembly of a polypeptide with an amino acid sequence similar to that of type-2 collagen, a sequential polypeptide consisting of the repetition of the Pro-Pro-Gly tripeptide was synthesized by solid-phase synthesis. Column chromatography of an ethanol solution of (Pro-Pro-Gly)₁₀ NH₂ showed the presence of a double helix or triple helix of the polypeptide. The pattern of a circular dichroism (CD) spectrum of an ethanol solution of (Pro-Pro-Gly)₁₀ NH₂ was very similar to that of an aqueous solution of (Pro-Pro-Gly)₁₀ OH, strongly suggesting the presence of a triple helix of the polypeptide in ethanol. An oriented monolayer assembly of (Pro-Pro-Gly)₁₀ NH₂ was formed on a thin gold film. The distribution of surface unevenness and the surface potential were investigated with Kelvin force microscopy. The rising spots carried an electric potential from room temperature to 150 °C. The correspondence showed the usefulness of the oriented monolayer of the sequential polypeptide materials for thermally stable, dielectric nanodevices. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3632–3639, 2003