Structural characterization and in vivo pro-tumor properties of a highly conserved matrikine

Elastin-derived peptides (EDPs) exert protumor activities by increasing tumor growth, migration and invasion. A number of studies have highlighted the potential of VGVAPG consensus sequence-derived elastin-like polypeptides whose physicochemical properties and biocompatibility are particularly suitable for in vivo applications, such as drug delivery and tissue engineering. However, among the EDPs, the influence of elastin-derived nonapeptides (xGxPGxGxG consensus sequence) remains unknown. Here, we show that the AGVPGLGVG elastin peptide (AG-9) present in domain-26 of tropoelastin is more conserved than the VGVAPG elastin peptide (VG-6) from domain-24 in mammals. The results demonstrate that the structural features of AG-9 and VG-6 peptides are similar. CD, NMR and FTIR spectroscopies show that AG-9 and VG-6 present the same conformation, which includes a mixture of random coils and β-turn structures. On the other hand, the supraorganization differs between peptides, as demonstrated by AFM. The VG-6 peptide gathers in spots, whereas the AG-9 peptide aggregates into short amyloid-like fibrils. An in vivo study showed that AG-9 peptides promote tumor progression to a greater extent than do VG-6 peptides. These results were confirmed by in vitro studies such as 2D and 3D proliferation assays, migration assays, adhesion assays, proteinase secretion studies and pseudotube formation assays to investigate angiogenesis. Our findings suggest the possibility that the AG-9 peptide present in patient sera may dramatically influence cancer progression and could be used in the design of new, innovative antitumor therapies.

Mutations in the ubiquitin-binding domain of OPTN/optineurin interfere with autophagy-mediated degradation of misfolded proteins by a dominant-negative mechanism

OPTN (optineurin) is an autophagy receptor and mutations in the OPTN gene result in familial glaucoma (E50K) and amyotrophic lateral sclerosis (ALS) (E478G). However, the mechanisms through which mutant OPTN leads to human diseases remain to be characterized. Here, we demonstrated that OPTN colocalized with inclusion bodies (IBs) formed by mutant HTT/huntingtin protein (mHTT) in R6/2 transgenic mice and IBs formed by 81QNmHTT (nuclear form), 109QmHTT (cytoplasmic form) or the truncated form of TARDBP/TDP-43 (TARDBP(ND251)) in Neuro2A cells. This colocalization required the ubiquitin (Ub)-binding domain (UbBD, amino acids 424 to 511) of OPTN. Overexpression of wild-type (WT) OPTN decreased IBs through K63-linked polyubiquitin-mediated autophagy. E50K or 210 to 410Δ (with amino acids 210 to 410 deleted) whose mutation or deletion was outside the UbBD decreased the IBs formed by 109QmHTT or TARDBP(ND251), as was the case with WT OPTN. In contrast, UbBD mutants, including E478G, D474N, UbBDΔ, 411 to 520Δ and 210 to 520Δ, increased accumulation of IBs. UbBD mutants (E478G, UbBDΔ) retained a substantial ability to interact with WT OPTN, and were found to colocalize with polyubiquitinated IBs, which might occur indirectly through their WT partner in a WT-mutant complex. They decreased autophagic flux evidenced by alteration in LC3 level and turnover and in the number of LC3-positive puncta under stresses like starvation or formation of IBs. UbBD mutants exhibited a weakened interaction with MYO6 (myosin VI) and TOM1 (target of myb1 homolog [chicken]), important for autophagosome maturation, in cells or sorted 109QmHtt IBs. Taken together, our data indicated that UbBD mutants acted as dominant-negative traps through the formation of WT-mutant hybrid complexes to compromise the maturation of autophagosomes, which in turn interfered with OPTN-mediated autophagy and clearance of IBs.

Elastomeric Polypeptide Biomaterials: Structure and Free Energy Transduction

The primary, secondary, tertiary and quaternary structures are presented and discussed for elastomeric polypeptides capable of undergoing inverse temperature transitions, that is, these polypeptides fold with the extrusion of water on raising the temperature through a transition. The elastomeric polypeptides, which are comprised of repeating peptide sequences, appear to be dominantly entropic elastomers. As these elastomers exhibit preferred secondary, tertiary and quarternary structure, they are not properly characterized as the random chain networks commonly ascribed to entropic elastomers. Instead, a mechanism of damping of internal chain dynamics on extension is described and referred to as the librational entropy mechanism of elasticity. Indeed, there are emerging a set of structural concepts for elastomeric polypeptides.

Of particular interest is that these elastomers are capable of exhibiting free energy transduction, e.g., thermomechanical and chemomechanical. A principle is stated for thermomechanical transduction and a postulate is given for chemomechanical transduction which is supported by prediction and experimental verification. The underlying mechanism is considered to be an aqueous(hydration) mediated apolar(hydrophobic)-polar interaction free energy which arises out of a competition between apolar and polar groups for limited waters of hydration. In general, there emerges a simple structural perspective of free energy transduction in elastomeric polypeptide biomaterials that involves thermal, mechanical or chemical means of altering the equilibrium between folded and unfolded states, where the folded states are dynamic helices called β-spirals with dominantly hydrophobic intramolecular interturn contacts and the unfolded states have the hydrophobic groups exposed to water.

Properties And Prevention of Adhesions Applications of Bioelastic Materials

The origins, syntheses, variable composition and physical properties of bioelastic materials are discussed. The latter includes their capacity to undergo inverse temperature transitions to increased order on raising the temperature and to be designable to interconvert free energies involving the intensive variables of mechanical force, temperature, pressure, chemical potential, electrochemical potential and light.

Bioelastic materials include analogues and other chemical variations of the viscoelastic polypeptide, poly(Val-Pro-Gly-Val-Gly), and cross-linked elastomeric matrices thereof. This parent material has been shown to be remarkably biocompatible; it can be minimally modified to vary the rate of hydrolytic breakdown; it can contain enzymatically reactive sites; and it can have cell attachment sites included which promote excellent cell adhesion, spreading and growth to confluence.

One specific application is in the prevention of postoperative adhesion. There are some 30,000,000 per year surgical procedures in this country and a large portion of these would benefit if a suitable material were available for preventing adhesions. Bioelastic materials have been tested in a contaminated peritoneal model, and promising preliminary studies have been carried out in the rabbit eye model for strabismus surgery. In the peritoneal model, 90% of the 29 control animals exhibited significant adhesions; whereas, only 20% of the 29 animals using gas sterilized matrices had significant adhesions. On the basis of this data, it appears that cross-linked poly(VPGVG) is an effective physical barrier to adhesion formation in a trauma model with resulting hemorrhage and contamination.

The potential use of bioelastic materials as a pericardial substitute following the more than 400,000 open heart surgeries per year in the U.S. is under development beginning with the use of bioelastic matrices to prevent adhesions to the total artificial heart being used as a bridge to heart transplantation such that the site will be less compromised when receiving the donor heart.

Molecular biophysics of elastin structure, function and pathology

Owing to the presence of the recurring sequence XPGX' (where X and X' are hydrophobic residues), the molecular structure of the sequences between cross-links in elastin is viewed primarily as a series of beta-turns which become helically ordered by hydrophobic folding into beta-spirals, which in turn assemble hydrophobically into twisted filaments. Both hydrophobic folding and assembly occur when the temperature is raised above Tt, the onset of an inverse temperature transition. Using poly[fv(VPGVG),fx(VPGXG)] (where fv and fx are mole fractions with fv + fx = 1 and X is now any of the naturally occurring amino acid residues), plots of fx versus Tt result in a new hydrophobicity scale based directly on the hydrophobic folding and assembly processes of interest. With the reference values chosen at fx = 1, the most hydrophobic residues of elastin, Tyr (Y) and Phe (F), have low values of Tt, -55 and -30 degrees C, respectively, and the most hydrophilic residues, Glu (E-), Asp (D-) and Lys (K+), have high values of 250, 170 and 120 degrees C, respectively. Raising the average value of Tt for a chain or chain segment from below to above physiological temperature drives hydrophobic unfolding and disassembly; lowering Tt does the reverse. This delta Tt mechanism has been used reversibly to interconvert many energy forms and is used here to explain initiating events of elastogenesis, pulmonary emphysema, solar elastosis and the paucity of elastic fibres in scar tissue. In general, oxidation and/or photolysis convert(s) hydrophobic residues into polar residues with the consequences of irreversibly raising Tt to above 37 degrees C, hydrophobic unfolding and disassembly (fibre swelling), and greater susceptibility to proteolysis.

The effect of a recombinant elastin-mimetic coating of an ePTFE prosthesis on acute thrombogenicity in a baboon arteriovenous shunt

A recombinant elastin-mimetic triblock protein polymer with an inverse transition temperature (approximately 20 degrees C) was used to impregnate small-diameter (4 mm i.d.) expanded polytetrafluoroethylene (ePTFE) vascular grafts. Scanning electron microscopy confirmed that initial elastin impregnation of the graft followed by further multilayer coating with elastin films filled in the fibril and node structure of the luminal surface of the ePTFE graft and was macroscopically smooth. Elastin protein polymer impregnation reduced the advancing contact angle of the luminal surface to 43 degrees, which was comparable to the advancing contact angle of 47 degrees for a cast elastin film. Attenuated total reflection infrared spectroscopy and Coomassie blue staining revealed little discernable change in the protein surface film after 24 h of shear at 500 s(-1) and 37 degrees C. Excellent short-term blood-contacting properties as determined by minimal fibrin and platelet deposition were demonstrated using a baboon extracorporeal femoral arteriovenous shunt model. The results of this study demonstrate the applicability of an elastin-mimetic triblock protein polymer as a non-thrombogenic coating or as a component of a tissue-engineered composite.

Effect of storage upon material properties of lyophilized porcine extracellular matrix derived from the urinary bladder

Xenogeneic extracellular matrices (ECMs) have been developed as off-the-shelf biologic scaffolds that have been effectively used in preclinical and clinical applications for tissue reconstruction. Such materials must be suitable for terminal sterilization and capable of storage for extended periods of time without significant changes in material properties and bioactivity. Material properties of interest for ECM scaffolds include hydrostatic permeability index (PI), uniaxial maximum load and elongation, maximum tangential stiffness (MTS), suture retention strength (SRS), and ball-burst strength (BBS). The present study evaluated these material properties for lyophilized forms of an ECM scaffold derived from the porcine urinary bladder, termed urinary bladder matrix (UBM), that was terminally sterilized by e-beam irradiation at 22 kGy and stored at room temperature (RT; 20-24 degrees C) or refrigerated temperature (REFT; 4-8 degrees C) for up to 12 months. UBM devices showed no change in SRS, BBS, and hydrostatic PI after the evaluation period. Lyophilized devices stored at RT showed an increase in maximum load and MTS while devices stored at REFT showed an increase in maximum elongation after 1 year of storage (p < 0.05). These results indicate that structural changes in the UBM device may slowly occur as a function of prolonged storage and storage temperature.

Comparative structures and properties of elastic proteins

Elastic proteins are characterized by being able to undergo significant deformation, without rupture, before returning to their original state when the stress is removed. The sequences of elastic proteins contain elastomeric domains, which comprise repeated sequences, which in many cases appear to form beta-turns. In addition, the majority also contain domains that form intermolecular cross-links, which may be covalent or non-covalent. The mechanism of elasticity varies between the different proteins and appears to be related to the biological role of the protein.

Elastomeric proteins: biological roles, structures and mechanisms

Elastomeric proteins are able to withstand significant deformations without rupture before returning to their original state when the stress is removed. Although elastomeric proteins differ considerably in their amino acid sequence, they all have a complex domain structure and share two common properties. Namely, they contain elastomeric domains, comprised of repeated sequences, and additional domains that form intermolecular crosslinks. Furthermore, several protein contain beta-turns as a structural motif within the elastomeric domains.

Short elastin-like peptides exhibit the same temperature-induced structural transitions as elastin polymers: implications for protein engineering

Elastin is a major protein component of the vascular wall and is responsible for its unusual elastic properties. Polymers of its repeating VPGVG sequences have been synthesised and shown to exhibit an inverse temperature transition where, as temperature rises, the polymer collapses from an extended chain to a beta-spiral structure with three VPGVG units per turn, each pentamer adopting a type II beta-turn conformation. These studies, however, have not established whether the temperature-driven conformational change is an intrinsic property of the individual pentameric sequences or a global, co-operative effect of many pentamers within the beta-spiral structure. Here, we examine by circular dichroism the behaviour of elastin-like peptides (VPGVG)n, where n varies between 1 and 5. Remarkably, we find that all lengths of peptide undergo an extended left and right arrow beta-turn transition with increasing temperature, suggesting that the induction of the beta-spiral occurs at the level of single pentameric units. The origin of this effect is a positive DeltaS term for the transition. At 35 degreesC, the average transition midpoint temperature, the value of TDeltaS is about 15 kcal mol-1. With larger oligomers (n=3), there is only a modest rise in DeltaS, suggesting that the dominant entropic effect resides within the monomer and that interactions between these units make only a small contribution to the energetics of the transition. Charges at the termini, and residue replacements or additions, regulate the transitions for the short peptides in a manner similar to that observed for the longer polymers. The behaviour of the same peptides in trifluoroethanol and SDS solutions is consistent with formation of the beta-turn being driven by interactions between non-polar groups. The significance of this behaviour for the rational design of temperature-induced responses in proteins is discussed.

Elastomeric polytetrapeptide matrices: hydrophobicity dependence of cell attachment from adhesive (GGIP)n to nonadhesive (GGAP)n even in serum

The cross-linked polytetrapeptide matrices based on the repeating amino acid sequences, GGAP, GGVP and GGIP, were prepared and tested for cell adhesion promoting activity in both the absence and presence of fetal bovine serum. For comparison, X20-poly(GVGVP), a matrix previously shown to be a poor support for cell attachment and spreading, was included. In the absence of serum, all three polytetrapeptide-based matrices and the polypentapeptide-based matrix were negative for the adhesion of fibroblasts and endothelial cells. In the presence of serum, various sub-maximal levels of cell adhesion were found for all matrices except for the matrix based on GGAP. An apparent correlation was noted between the degree of cell attachment to the different polytetrapeptide-based matrices and the hydrophobicity of those matrices where increased hydrophobicity results in increased cell attachment. The property of being refractory to ligamentum nuchae fibroblast and human umbilical vein endothelial cell adhesion in the presence of serum indicates a potential use for X20-poly(GGAP) in the development of, for example, additional physical barriers for the prevention of post-surgical and post-trauma adhesions.

Self-assembly of bioelastomeric structures from solutions: mean-field critical behavior and Flory-Huggins free energy of interactions

Elastic and quasi-elastic light scattering studies were performed on aqueous solutions of poly(Val-Pro-Gly-Gly), a representative synthetic bioelastomer that differs from the previously studied poly(Val-Pro-Gly-Val-Gly) by the deletion of the hydrophobic Val in position four. When the spinodal line was approached from the region of thermodynamic stability, the intensity of light scattered by fluctuations, and the related lifetime and correlation length, were observed to diverge with mean-field critical exponents for both systems. Fitting of the experimental data allowed determining the spinodal and binodal (coexistence) lines that characterize the phase diagrams of the two systems, and it also allowed a quantitative sorting out of the enthalpic and entropic contributions to the Flory-Huggins interaction parameters. The contribution of valine is derived by comparison of the two cases. This can be viewed as sorting out the effect of a modulation of the solute. The same approach may allow sorting out the entropic and enthalpic effect of modulations of the solvent by cosolutes (or by cosolvents). This could be of particular interest in the case of small osmolytes, affording important adaptive roles in nature, at the cost of very limited changes in genetic information. Finally, the suggestion is further supported that statistical fluctuations of anomalous amplitude, such as those occurring in proximity of the spinodal line, have a role in promoting the process of self-assembly of extended supramolecular structures. On the practical side, the present approach appears useful in the design of novel synthetic model systems for bioelastomers.

Synthesis of 4% Glu-containing Val1 and Ile1-polypentapeptides: model protein systems for demonstrating mechanochemical coupling

The synthesis of 4% Glu-polypentapeptide (PPP) (i.e., 4 Glu residues per 100 amino acid residues) and 4% Glu-Ile1-PPP, in which Val1 is substituted by a more hydrophobic Ile residue, is carried out by copolymerizing the p-nitrophenyl-active esters of GE(OMe)GVP and GE(OMe)GIP with their parent pentamers GVGVP and GVGIP in 1:4 ratios, respectively. After removal of the methyl ester on the side chain of Glu, these polymers exhibited a remarkable pH dependence of the temperature for their inverse temperature transitions, which are followed as turbidity development at 300 nm. On gamma-irradiation crosslinking, the elastomeric bands obtained exhibited a pH-mediated contraction and relaxation. Thus, for the first time, mechanochemical coupling is demonstrated in a synthetic polypeptide system. That the basic mechanism involves the hydrophobic effect (chemical modulation of an inverse temperature transition) and not ion-ion electrostatic repulsion is also discussed.

pK shift of functional group in mechanochemical coupling due to hydrophobic effect: evidence for an apolar-polar repulsion free energy in water

In the sequential polypeptide poly[4(VPGVG),(VPGEG)] and its more hydrophobic analog poly[4(IPGVG),(IPGEG)] when the material is gamma-irradiation cross-linked to form an elastomeric matrix, mechanochemical coupling occurs on changing the pH, that is, motion and mechanical work are achieved by a change in proton chemical potential. The temperature dependence of aggregation at different pH values in phosphate buffered saline demonstrates the pK to be shifted approximately one pH unit higher for the more hydrophobic sequential polypeptide. The pH dependence of contraction or relaxation for each elastomer shows a similar shift. Data are reviewed and 2D-NMR data are presented which argue that the pK shift is not due to different conformations of the polypentapeptides. Specifically it is proposed that there exist a competition between carboxylates and hydrophobic side chains for mutually incompatible water structures; this results in an apolar-polar repulsion free energy in water with the difference in free energy reflecting the difference in the lle and Val hydrophobicities.

A method for fixation of elastin demonstrated by stress/strain characterization

In the process of examining the effects of oxidants on the mechanical properties of purified ligamentum nuchae elastin, it was found that sodium hypochlorite as constituted in Clorox will fix elastin at any preset extension. The treatments were carried out at a 1 to 5 dilution and at 0, 20 and 40% extensions. In each case, the new resting length was near the preset length and the elastic modulus increased remarkably, for example, from 1 to 5 x 10(7) dynes/cm2 for the sample preset at 20% extension. As reflected in the increased elastic modulus, the fixation was achieved by the formation of irreversible cross-links. Due to the near absence of side chains containing chemically reactive groups suitable for contributing to the formation of additional cross-links required in fixation, this is the first method whereby irreversible fixation of elastin has been achieved. The absence of a suitable fixative for elastic tissues such as lung, arteries, etc. has limited the microscopic characterization of functional extended states of these tissues.

Entropic elastic processes in protein mechanisms. I. Elastic structure due to an inverse temperature transition and elasticity due to internal chain dynamics

Numerous physical characterizations clearly demonstrate that the polypentapeptide of elastin (Val1-Pro2-Gly3-Val4-Gly5)n in water undergoes an inverse temperature transition. Increase in order occurs both intermolecularly and intramolecularly on raising the temperature from 20 to 40 degrees C. The physical characterizations used to demonstrate the inverse temperature transition include microscopy, light scattering, circular dichroism, the nuclear Overhauser effect, temperature dependence of composition, nuclear magnetic resonance (NMR) relaxation, dielectric relaxation, and temperature dependence of elastomer length. At fixed extension of the cross-linked polypentapeptide elastomer, the development of elastomeric force is seen to correlate with increase in intramolecular order, that is, with the inverse temperature transition. Reversible thermal denaturation of the ordered polypentapeptide is observed with composition and circular dichroism studies, and thermal denaturation of the crosslinked elastomer is also observed with loss of elastomeric force and elastic modulus. Thus, elastomeric force is lost when the polypeptide chains are randomized due to heating at high temperature. Clearly, elastomeric force is due to nonrandom polypeptide structure. In spite of this, elastomeric force is demonstrated to be dominantly entropic in origin. The source of the entropic elastomeric force is demonstrated to be the result of internal chain dynamics, and the mechanism is called the librational entropy mechanism of elasticity. There is significant application to the finding that elastomeric force develops due to an inverse temperature transition. By changing the hydrophobicity of the polypeptide, the temperature range for the inverse temperature transition can be changed in a predictable way, and the temperature range for the development of elastomeric force follows. Thus, elastomers have been prepared where the development of elastomeric force is shifted over a 40 degrees C temperature range from a midpoint temperature of 30 degrees C for the polypentapeptide to 10 degrees C by increasing hydrophobicity with addition of a single CH2 moiety per pentamer and to 50 degrees C by decreasing hydrophobicity.(ABSTRACT TRUNCATED AT 400 WORDS)