Minimal Lipidation Stabilizes Protein-Like Molecular Architecture

Bottom-up design of biomimetic assemblies

Nature has evolved the ability to assemble a variety of molecules into functional architectures that can specifically bind cellular ligands. Mimicking this strategy requires the design of a set of multifaceted molecules, where elements that direct assembly were conjugated to biologically specific components. The development of functional molecular building-blocks that assemble to form compartments for therapeutics addresses the desire to have controllable morphologies that interact with biological interfaces at nanometer length scales. The practical application of such 'bottom-up' assemblies requires the ability to predict the type of aggregated structure and to synthesize molecules in a highly controlled fashion. This bottom-up approach results in a molecular platform that mimics biological systems with potential for encapsulating and delivering drug molecules.

Differential modulation of human melanoma cell metalloproteinase expression by alpha2beta1 integrin and CD44 triple-helical ligands derived from type IV collagen

Tumor cell binding to components of the basement membrane is well known to trigger intracellular signaling pathways. Signaling ultimately results in the modulation of gene expression, facilitating metastasis. Type IV collagen is the major structural component of the basement membrane and is known to be a polyvalent ligand, possessing sequences bound by the alpha1beta1, alpha2beta1, and alpha3beta1 integrins, as well as cell surface proteoglycan receptors, such as CD44/chondroitin sulfate proteoglycan (CSPG). The role of alpha2beta1 integrin and CD44/CSPG receptor binding on human melanoma cell activation has been evaluated herein using triple-helical peptide ligands incorporating the alpha1(IV)382-393 and alpha1(IV)1263-1277 sequences, respectively. Gene expression and protein production of matrix metalloproteinases-1 (MMP-1), -2, -3, -13, and -14 were modulated with the alpha2beta1-specific sequence, whereas the CD44-specific sequence yielded significant stimulation of MMP-8 and lower levels of modulation of MMP-1, -2, -13, and -14. Analysis of enzyme activity confirmed different melanoma cell proteolytic potentials based on engagement of either the alpha2beta1 integrin or CD44/CSPG. These results are indicative of specific activation events that tumor cells undergo upon binding to select regions of basement membrane collagen. Based on the present study, triple-helical peptide ligands provide a general approach for monitoring the regulation of proteolysis in cellular systems.

Analysis of matrix metalloproteinase triple-helical peptidase activity with substrates incorporating fluorogenic L- or D-amino acids

The consequences of improper regulation of collagen turnover include diseases such as tumor cell metastasis and arthritis. Several fluorogenic triple-helical peptide (fTHP) substrates have been constructed presently to examine collagenolytic behavior. These substrates incorporate L- or D-2-amino-3-(7-methoxy-4-coumaryl)propionic acid (Amp) or L- or D-2-amino-3-(6,7-dimethoxy-4-coumaryl)propionic acid (Adp) as the fluorophore and N-2,4-dinitrophenyl (Dnp) as the quencher. The desired sequences were C6-(Gly-Pro-Hyp)5-Gly-Pro-[Amp/Adp]-Gly-Pro-Gln-Gly approximately Leu-Arg-Gly-Gln-Lys(Dnp)-Gly-Val-Arg-(Gly-Pro-Hyp)5-NH2. All four fTHPs formed stable triple-helices. Matrix metalloproteinase-2 (MMP-2) rates of hydrolysis for all fTHPs were considerably more rapid than corresponding MMP-1 rates. Evaluation of individual kinetic parameters indicated that MMP-2 bound to the fTHPs more efficiently than MMP-1. Comparison to a triple-helical substrate incorporating the same sequence but with a different fluorophore [Lys((7-methoxycoumarin-4-yl)acetyl); Lys(Mca)] demonstrated that the shorter side chain of Amp or Adp was better tolerated by MMP-1 and MMP-2. Adp may well be the fluorophore of choice for fTHPs, as (a) fTHPs incorporating Adp were obtained in significantly higher yields than the Amp-containing fTHPs, (b) Adp has a larger Stokes shift than either Amp or Lys(Mca) and thus has less chance of self-quenching, (c) Adp has a relatively high quantum yield, (d) the Adp/Dnp pair is compatible with multiwell plate reader formats, and (e) MMPs better tolerate Adp than Lys(Mca).

Angiogenesis in collagen I requires alpha2beta1 ligation of a GFP*GER sequence and possibly p38 MAPK activation and focal adhesion disassembly

Angiogenesis depends on proper collagen biosynthesis and cross-linking, and type I collagen is an ideal angiogenic scaffold, although its mechanism is unknown. We examined angiogenesis using an assay wherein confluent monolayers of human umbilical vein endothelial cells were overlain with collagen in a serum-free defined medium. Small spaces formed in the cell layer by 2 h, and cells formed net-like arrays by 6-8 h and capillary-like lumens by 24 h. Blocking of alpha2beta1, but not alpha1 or alpha(v)beta3 integrin function halted morphogenesis. We found that a triple-helical, homotrimeric peptide mimetic of a putative alpha2beta1 binding site: alpha1(I)496-507 GARGERGFP*GER (where single-letter amino acid nomenclature is used, P* = hydroxyproline) inhibited tube formation, whereas a peptide carrying another putative site: alpha1(I)127-138 GLP*GERGRP*GAP* or control peptides did not. A chemical inhibitor of p38 mitogen-activated protein kinase (p38 MAPK), SB202190, blocked tube formation, and p38 MAPK activity was increased in collagen-treated cultures, whereas targeting MAPK kinase (MEK), focal adhesion kinase (FAK), or phosphatidylinositol 3-kinase (PI3K) had little effect. Collagen-treated cells had fewer focal adhesions and 3- to 5-fold less activated FAK. Thus capillary morphogenesis requires endothelial alpha2beta1 integrin engagement of a single type I collagen integrin-binding site, possibly signaling via p38 MAPK and focal adhesion disassembly/FAK inactivation.

Matrix metalloproteinases and collagen catabolism

The matrix metalloproteinase (MMP)/matrixin family has been implicated in both normal tissue remodeling and a variety of diseases associated with abnormal turnover of extracellular matrix components. The mechanism by which MMPs catabolize collagen (collagenolysis) is still largely unknown. Substrate flexibility, MMP active sites, and MMP exosites all contribute to collagen degradation. It has recently been demonstrated that the ability to cleave a triple helix (triple-helical peptidase activity) can be distinguished from the ability to cleave collagen (collagenolytic activity). This suggests that the ability to cleave a triple helix is not the limiting factor for collagenolytic activity-the ability to properly orient and potentially destabilize collagen is. For the MMP family, the catalytic domain can unwind and cleave a triple-helical structure, while the C-terminal hemopexin-like domain appears to be responsible for properly orienting collagen and destabilizing it to some degree. It is also possible that exosites within the catalytic and/or C-terminal hemopexin-like domain may exclude some MMPs from cleaving collagen. Overall, it appears that many proteases of distinct mechanisms possess triple-helical peptidase activity, and that convergent evolution led to a few proteases possessing collagenolytic activity. Proper orientation and distortion of the triple helix may be the key factor for collagenolysis.

Structure and function of integral membrane protein domains resolved by peptide-amphiphiles: application to phospholamban

We have used synthetic lipidated peptides ("peptide-amphiphiles") to study the structure and function of isolated domains of integral transmembrane proteins. We used 9-fluorenylmethyloxycarbonyl (Fmoc) solid-phase peptide synthesis to prepare full-length phospholamban (PLB(1-52)) and its cytoplasmic (PLB(1-25)K: phospholamban residues 1-25 plus a C-terminal lysine), and transmembrane (PLB(26-52)) domains, and a 38-residue model alpha-helical sequence as a control. We created peptide-amphiphiles by linking the C-terminus of either the isolated cytoplasmic domain or the model peptide to a membrane-anchoring, lipid-like hydrocarbon tail. Circular dichroism measurements showed that the model peptide-amphiphile, either in aqueous suspension or in lipid bilayers, had a higher degree of alpha-helical secondary structure than the unlipidated model peptide. We hypothesized that the peptide-amphiphile system would allow us to study the function and structure of the PLB(1-25)K cytoplasmic domain in a native-like configuration. We compared the function (inhibition of the Ca-ATPase in reconstituted membranes) and structure (via CD) of the PLB(1-25) amphiphile to that of PLB and its isolated transmembrane and cytoplasmic domains. Our results indicate that the cytoplasmic domain PLB(1-25)K has no effect on Ca-ATPase (calcium pump) activity, even when tethered to the membrane in a manner mimicking its native configuration, and that the transmembrane domain of PLB is sufficient for inhibition of the Ca-ATPase.

Non-covalent stabilization of a beta-hairpin peptide into liposomes

An oligopeptide modified on both the N- and C-termini with hydrophobic moieties was prepared on a solid phase and anchored into a liposome, stabilizing the fold of the peptide into a beta-hairpin, which would otherwise be a random coil.

Selective hydrolysis of triple-helical substrates by matrix metalloproteinase-2 and -9

The role of proteases in the tumor cell invasion process is multifaceted. Members of the matrix metalloproteinase (MMP) family have been implicated in primary and metastatic tumor growth, angiogenesis, and degradation of extracellular matrix (ECM) components. Differentiating between the up-regulation of MMP production and the presence of activated MMPs can be difficult but may well dictate which MMPs are critical to invasion. Because the hydrolysis of collagens is one of the committed steps in ECM turnover, we have investigated selective MMP action on collagenous substrates as a means to evaluate active MMPs. Two triple-helical peptide (THP) models of the MMP-9 cleavage site in type V collagen, alpha1(V)436-450 THP and alpha1(V)436-447 fTHP, were hydrolyzed by MMP-2 and MMP-9 at the Gly-Val bond, analogous to the bond cleaved by MMP-9 in the corresponding native collagen. Kinetic analyses showed k(cat)/K(m) values of 14,002 and 5,449 s(-1)m(-1) for MMP-2 and -9 hydrolysis of alpha1(V)436-447 fTHP, respectively. These values, along with individual k(cat) and K(m) values, are comparable with collagen hydrolysis by MMP-2 and -9. Neither THP was hydrolyzed by MMP-1, -3, -13, or -14. alpha1(V)436-447 fTHP and a general fluorogenic THP were used to screen for triple-helical peptidase activity in alpha(2)beta(1) integrin-stimulated melanoma cells. Binding of the alpha(2)beta(1) integrin resulted in the production of substantial triple-helical peptidase activity, the majority (>95%) of which was non-MMP-2/-9. THPs were found to provide highly selective substrates for members of the MMP family and can be used to evaluate active MMP production in cellular systems.

Melanoma cell CD44 interaction with the alpha 1(IV)1263-1277 region from basement membrane collagen is modulated by ligand glycosylation

Invasion of the basement membrane is believed to be a critical step in the metastatic process. Melanoma cells have been shown previously to bind distinct triple-helical regions within basement membrane (type IV) collagen. Additionally, tumor cell binding sites within type IV collagen contain glycosylated hydroxylysine residues. In the present study, we have utilized triple-helical models of the type IV collagen alpha1(IV)1263-1277 sequence to (a) determine the melanoma cell receptor for this ligand and (b) analyze the results of single-site glycosylation on melanoma cell recognition. Receptor identification was achieved by a combination of methods, including (a) cell adhesion and spreading assays using triple-helical alpha1(IV)1263-1277 and an Asp(1266)Abu variant, (b) inhibition of cell adhesion and spreading assays, and (c) triple-helical alpha1(IV)1263-1277 affinity chromatography with whole cell lysates and glycosaminoglycans. Triple-helical alpha1(IV)1263-1277 was bound by melanoma cell CD44/chondroitin sulfate proteoglycan receptors and not by the collagen-binding integrins or melanoma-associated proteoglycan. Melanoma cell adhesion to and spreading on the triple-helical alpha1(IV)1263-1277 sequence was then compared for glycosylated (replacement of Lys(1265) with Hyl(O-beta-d-galactopyranosyl)) versus non-glycosylated ligand. Glycosylation was found to strongly modulate both activities, as adhesion and spreading were dramatically decreased due to the presence of galactose. CD44/chondroitin sulfate proteoglycan did not bind to glycosylated alpha1(IV)1263-1277. Overall, this study (a) is the first demonstration of the prophylactic effects of glycosylation on tumor cell interaction with the basement membrane, (b) provides a rare example of an apparent unfavorable interaction between carbohydrates, and (c) suggests that sugars may mask "cryptic sites" accessible to tumor cells with cell surface or secreted glycosidase activities.

Triple-helical peptide analysis of collagenolytic protease activity

Matrix metalloproteinase (MMP) family members are involved in the physiological remodeling of tissues and embryonic development as well as pathological destruction of extracellular matrix components. To study the mechanisms of MMP action on collagenous substrates, non-fluorogenic and fluorogenic triple-helical peptide models of MMP-1 cleavage sites in interstitial collagens have been constructed. Triple-helical peptides were assembled by either (a) covalent branching or (b) self-association driven by hydrophobic interactions. Fluorogenic triple-helical peptide (fTHP) substrates contained the fluorophore/quencher pair of (7-methoxycoumarin-4-yl)acetyl (Mca) and N-2,4-dinitrophenyl (Dnp) in the P5 and P5' positions, respectively. Investigation of MMP family hydrolysis of THPs showed kcat/Km values in the order of MMP-13 > MMP-1 approximately MMP-1(delta243-450) approximately MMP-2 >> MMP-3. Studies on the effect of temperature on fTHP and an analogous fluorogenic single-stranded peptide (fSSP) hydrolysis by MMP-1 showed that the activation energies between these two substrates differed by 3.4-fold, similar to the difference in activation energies for MMP-1 hydrolysis of type I collagen and gelatin. The general proteases trypsin and thermolysin were also studied for triple-helical peptidase activity. Both of these enzymes exhibited similar activation energies to MMP-1 for hydrolysis of fTHP versus fSSP. These results suggest that 'triple-helical peptidase' activity can be distinguished from 'collagenolytic' activity, and that mechanistically distinct enzymes convergently evolved to develop collagenolytic activity.

Peptide-amphiphile nanofibers: a versatile scaffold for the preparation of self-assembling materials

Twelve derivatives of peptide-amphiphile molecules, designed to self-assemble into nanofibers, are described. The scope of amino acid selection and alkyl tail modification in the peptide-amphiphile molecules are investigated, yielding nanofibers varying in morphology, surface chemistry, and potential bioactivity. The results demonstrate the chemically versatile nature of this supramolecular system and its high potential for manufacturing nanomaterials. In addition, three different modes of self-assembly resulting in nanofibers are described, including pH control, divalent ion induction, and concentration.

Induction of protein-like molecular architecture by monoalkyl hydrocarbon chains

Numerous approaches have been described for creating relatively small folded biomolecular structures. "Peptide-amphiphiles," whereby monoalkyl or dialkyl hydrocarbon chains are covalently linked to peptide sequences, have been shown previously to form specific molecular architecture of enhanced stability. The present study has examined the use of monoalkyl hydrocarbon chains as a more general method for inducing protein-like structures. Peptide and peptide-amphiphiles have been characterized by CD and one- and two-dimensional nmr spectroscopic techniques. We have examined two structural elements: alpha-helices and collagen-like triple helices. The alpha-helical propensity of a 16-residue peptide either unmodified or acylated with a C(6) or C(16) monoalkyl hydrocarbon chain has been examined initially. The 16-residue peptide alone does not form a distinct structure in solution, whereas the 16-residue peptide adopts predominantly an alpha-helical structure in solution when a C(6) or C(16) monoalkyl hydrocarbon chain is N-terminally acylated. The thermal stability of the alpha-helix is greater upon addition of the C(16) compared with the C(6) chain, which correlates to the extent of aggregation induced by the respective hydrocarbon chains. Very similar results are seen using a 39-residue triple-helical model peptide, in that structural thermal stability (a) is increasingly enhanced as alkyl chain length is increased and (b) correlates to the extent of peptide-amphiphile aggregation. Overall, structures as diverse as alpha-helices, triple helices, and turns/loops have been shown to be induced and/or stabilized by alkyl chains. Increasing alkyl chain length enhances stability of the structural element and induces aggregates of defined sizes. Hydrocarbon chains may be useful as general tools for protein-like structure initiation and stabilization as well as biomaterial modification.

Use of Edman degradation sequence analysis and matrix-assisted laser desorption/ionization mass spectrometry in designing substrates for matrix metalloproteinases

The matrix metalloproteinase (MMP) family has been implicated in the process of a variety of diseases such as arthritis, atherosclerosis, and tumor cell metastasis. We have been designing single-stranded peptides (SSPs) and triple-helical peptides (THPs) as potential discriminatory MMP substrates. Edman degradation sequence and matrix-assisted laser desorption/ionization mass spectrometric (MALDI-MS) analyses of proteolytic activity have been utilized to aid in further substrate design. THP models of the alpha1(I)772-786 sequence from type I collagen were synthesized to examine the triple-helical substrate specificity of MMP family members. Sequence and MALDI-MS analyses were used in conjunction with a fluorometric assay to determine the exact point of cleavage by each MMP. MMP-1 (interstitial collagenase) cleaved the substrates at a single Gly-Ile bond, analogous to the cleavage site in type I collagen. MMP-2 (Mr 72 000 type IV collagenase; gelatinase A) was found to cleave the substrates at two sites, a Gly-Ile bond and a Gly-Gln bond. MMP-3 (stromelysin 1) was found to cleave only one of the substrates after reaction for 48 h. Ultimately, sequence and MALDI-MS analyses allowed us to detect an additional cleavage site for MMP-2 in comparison to MMP-1, while MMP-3 was found to cleave a substrate after an extended time period. The second cleavage site would cause the kinetic parameters for MMP-2 to be overestimated by the fluorometric assay. Further design variations for these substrates need to consider the presence of more stable triple-helical conformation (to eliminate MMP-3 binding) and the removal of Gly-Gln bonds that may be susceptible to MMP-2.

Self-assembled peptide fibers from valylvaline bola-amphiphiles by a parallel beta-sheet network

A series of dipeptide-based bola-amphiphiles, bis(N-alpha-amide-L-valyl-L-valine) 1, n-alkane dicarboxylate (n=4-12), have been synthesized. The bola-amphiphiles with n=4 and 6 self-assembled to form crystalline solids in water, whereas those with n=7-12 produced peptide fibers. FT-IR spectroscopy and X-ray diffraction patterns revealed that the peptide fibers have parallel-type beta-sheet networks between the valylvaline units. FT-IR deconvolution study of carboxyl regions indicated that these crystalline solids and peptide fibers are stabilized by interlayer bifurcated and intralayer lateral hydrogen-bond networks between the end carboxylic acid groups, respectively.

Chemical synthesis of proteins

The manipulation of protein structure enables a better understanding of the principles of protein folding, as well as the development of novel therapeutics and drug-delivery vehicles. Chemical synthesis is the most powerful approach for constructing proteins of novel design and structure, allowing for variation of covalent structure without limitations. Here we describe the various chemical methods that are currently used for creating proteins of unique architecture and function.

Hydrolysis of triple-helical collagen peptide models by matrix metalloproteinases

The matrix metalloproteinase (MMP) family has been implicated in the process of a variety of diseases such as arthritis, atherosclerosis, and tumor cell metastasis. To study the mechanisms of MMP action on collagenous substrates, we have constructed homotrimeric triple-helical peptide (THP) models of the collagenase cleavage sites in types I and II collagen. The THPs incorporate either the alpha1(I)772-786 or the alpha1(II)772-783 sequence. The alpha1(I)772-786 and alpha1(II)772-783 THPs were hydrolyzed by MMP-1 at the Gly-Ile and Gly-Leu bonds, respectively, analogous to the bonds cleaved in corresponding native collagens. Thus, the THPs contained all necessary information to direct MMP-1 binding and proteolysis. Subsequent investigations using the alpha1(I)772-786 THP showed hydrolysis by MMP-2, MMP-13, and a COOH-terminal domain-deleted MMP-1 (MMP-1(Delta(243-450))) but not by MMP-3 or a COOH-terminal domain-deleted MMP-3 (MMP-3(Delta(248-460))). Kinetic analyses showed a k(cat)/K(m) value of 1,808 s(-1) m(-1) for MMP-1 hydrolysis of alpha1(I)772-786 THP, approximately 10-fold lower than for type I collagen. The effect is caused primarily by relative K(m) values. MMP-2 and MMP-13 cleaved the THP more rapidly than MMP-1, but MMP-2 cleavage occurred at distinct multiple sites. Comparison of MMP-1 and MMP-1(Delta(243-450)) hydrolysis of alpha1(I)772-786 THP showed that both can cleave a triple-helical substrate with a slightly higher K(m) value for MMP-1(Delta(243-450)). We propose that the COOH-terminal domain of MMPs is necessary for orienting whole, native collagen molecules but may not be necessary for binding to and cleaving a THP. This proposal is consistent with the large distance between the MMP-1 catalytic and COOH-terminal domains observed by three-dimensional structural analysis and supports previous suggestions that the features of the catalytic domain contribute significantly toward enzyme specificity.

Conformational analysis and stability of collagen peptides by CD and by 1H- and 13C-NMR spectroscopies

Four small type I collagen CNBr peptides containing complete natural sequences were purified from bovine skin and investigated by CD and 1H- and 13C-nmr spectroscopies to obtain information concerning their conformation and thermal stability. CD showed that a triple helix was formed at 10 degrees C in acidic aqueous solution by peptide alpha l(I) CB2 only, and to lesser extent, by alpha 1(I) CB4, whereas peptides alpha 1(I) CB5 and alpha 2(I) CB2 remained unstructured. Analytical gel filtration confirmed that peptides alpha 1(I) CB2 and alpha 1(I) CB4 only were able to form trimeric species at temperature between 14 and 20 degrees C, and indicated that the monomer = trimer equilibrium was influenced by the chaotropic nature of the salt present in the eluent, by its concentration, and by temperature variations. CD measurements at increasing temperatures showed that alpha 1(I) CB2 was less stable than its synthetic counterpart due to incomplete prolyl hydroxylation of the preparation from the natural source. 1H- and 13C-nmr spectra acquired in the temperature range 0-47 and 0-27 degrees C, respectively, indicated that with decreasing temperature the most abundant from of alpha 1(I) CB2 was in slow exchange with an assembled form, characterized by broad lines, as expected for the triple-helical conformation. A large number of trimer cross peaks was observed both in the proton and carbon spectra, and these were most likely due to the nonequivalence of the environments of the three chains in the triple helix. This nonequivalence may have implications for the aggregation of collagen molecules and for collagen binding to other molecules. The thermal transition from trimer to monomer was also monitored by 1H-nmr following the change in area of the signal belonging to one of the two beta protons of the C-terminal homoserine. The unfolding process was found to be fully reversible with a melting temperature of 13.4 degrees C, in agreement with CD results. The qualitative superposition of the melting curves obtained by CD for the peptide bond characteristics and by nmr for a side chain suggests that triple-helical backbone and side chains constitute a single unit.

Cellular recognition of synthetic peptide amphiphiles in self-assembled monolayer films

The incorporation of lipidated cell adhesion peptides into self-assembled structures such as films provides the opportunity to develop unique biomimetic materials with well-organized interfaces. Synthetic dialkyl tails have been linked to the amino-terminus, carboxyl-terminus, and both termini of the cell recognition sequence Arg-Gly-Asp (RGD) to produce amino-coupled, carboxyl-coupled, and looped RGD peptide amphiphiles. All three amphiphilic RGD versions self-assembled into fairly stable mixed monolayers that deposited well as Langmuir-Blodgett films on surfaces, except for films containing amino-coupled RGD amphiphiles at high peptide concentrations. FT-IR studies showed that amino-coupled RGD head groups formed the strongest lateral hydrogen bonds. Melanoma cells spread on looped RGD amphiphiles in a concentration-dependent manner, spread indiscriminately on carboxyl-coupled RGD amphiphiles, and did not spread on amino-coupled RGD amphiphiles. Looped RGD amphiphiles promoted the adhesion, spreading, and cytoskeletal reorganization of melanoma and endothelial cells while control looped Arg-Gly-Glu (RGE) amphiphiles inhibited them. Antibody inhibition of the integrin receptor alpha3beta1 blocked melanoma cell adhesion to looped RGD amphiphiles. These results confirm that novel biomolecular materials containing synthetic peptide amphiphiles have the potential to control cellular behavior in a specific manner.

Induction of protein-like molecular architecture by self-assembly processes

One of the most intriguing self-assembly processes is the folding of peptide chains into native protein structures. We have developed a method for building protein-like structural motifs that incorporate sequences of biological interest. A lipophilic moiety is attached onto an N(alpha)-amino group of a peptide chain, resulting in a 'peptide-amphiphile'. The alignment of amphiphilic compounds at the lipid solvent interface is used to facilitate peptide alignment and structure initiation and propagation. Peptide-amphiphiles containing potentially triple-helical structural motifs have been synthesized. The resultant head group structures have been characterized by circular dichroism and NMR spectroscopies. Evidence for a self-assembly process of peptide-amphiphiles has been obtained from: (a) circular dichroism spectra and melting curves characteristic of triple-helices, (b) one- and two-dimensional NMR spectra indicative of stable triple-helical structure at low temperatures and melted triple-helices at high temperatures, and (c) pulsed-field gradient NMR experiments demonstrating different self-diffusion coefficients between proposed triple-helical and non-triple-helical species. The peptide-amphiphiles described here provide a simple approach for building stable protein structural motifs using peptide head groups.