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D W Urry

Publications and source records attributed to D W Urry.

At least 37 records · Page 2Linked to original sources
PubMed1995

Synthesis and characterization of the human elastin W4 sequence.

Following the nomenclature of Sandberg, the W4 sequence of human elastin, [sequence: see text], has been synthesized by solid-phase methods and characterized by carbon-13 nuclear magnetic resonance, amino-acid analysis, mass spectra and elemental analysis. This sequence was then polymerized to greater than 50 kDa as determined by retention in 50 kDa molecular weight cut-off dialysis tubing. It has been successfully cross-linked by gamma-irradiation (20 Mrad) to form an elastomeric matrix, designated as X20-poly(W4). Physical characterizations such as stress/strain, thermolelasticity, acid-base titration and inverse temperature transition studies have been carried out on this elastomer, which is homologous to the striking, poly(VPGVG), W4 sequence of bovine and porcine elastins. These results are compared with previous results on the polypentapeptide of elastin, (VPGVG)n, and it has been demonstrated that X20-poly(W4) also is a dominantly entropic elastomer. Finally, the working model for the structure of this human elastin sequence was derived computationally using molecular mechanics and dynamics calculations. Thus the human W4 sequence appears to be structurally and functionally equivalent to the bovine and porcine W4 sequences in spite of the less regular repeating pentamer sequence.

Amino Acid Sequence↗
PubMed1994

Electromechanical transduction: reduction-driven hydrophobic folding demonstrated in a model protein to perform mechanical work.

It has long been appreciated that hydrophobic folding is an important element of protein structure formation. Here it is demonstrated for the first time that the electrochemical or chemical reduction of a nicotinamide in a model protein, which increases hydrophobicity, can drive hydrophobic folding and assembly in such a way as to lift a weight or otherwise contract against a constant tensional force. The model protein, poly[0.73(GVGVP),0.27(GK(NMeN)GVP], can be gamma-irradiation cross-linked to form an elastic matrix which contracts on raising the temperature from below to above the transition range for hydrophobic folding and assembly. On reduction of the N-methyl nicotinamide, (NMeN), the transition temperature range is lowered from above to below 20 degrees C to drive contraction due to hydrophobic folding with the performance of mechanical work.

Amino Acid Sequence↗
PubMed1994

Nanometric design of extraordinary hydrophobic-induced pKa shifts for aspartic acid: relevance to protein mechanisms.

Commonly a key element enabling proteins to function is an amino acid residue or residues with functional side chains having shifted pKa values. This article reports the results on a set of protein-based polymers (model proteins) that exhibit hydrophobic folding and assembly transitions, and that have been designed for the purpose of achieving large hydrophobic-induced pKa shifts by selectively replacing Val residues by Phe residues. The high molecular weight polypentapeptides, actually poly(tricosapeptides) with six varied pentamers in fixed sequence, were designed and synthesized to have the same amino acid compositions but different proximities between a single aspartic acid residue and 5 Phe residues per 30 residues. With the 5 Phe residues distal from the Asp residue, the observed pKa shift was 2.9 when compared to the Val-containing reference. With the 5 Phe residues within 1 nm of the Asp residue, the pKa shift was 6.2. This represents a free energy of interaction of 8 kcal/mole. To our knowledge, this is the largest pKa shift documented for an Asp residue in a polypeptide- or protein-water system. Data are reviewed that do not support the usual electrostatic arguments for pKa shifts of charge-charge repulsion and/or unfavorable ion self-energies arising from displacement of water by hydrophobic moieties, but rather the data are interpreted to indicate the presence of an apolar-polar repulsive free energy of hydration, which results from a potentially highly cooperative competition between apolar and polar species for hydration.

Amino Acid Sequence↗
PubMed1994

Use of polypentapeptides of elastin to prevent postoperative adhesions: efficacy in a contaminated peritoneal model.

We investigated the use of a sheet of polypentapeptide of elastin as a physical barrier to adhesion formation in a contaminated peritoneal wound model. A total of 88 rats were studied with random assignment of animals to three study groups; control (29), polypentapeptide steam sterilized (30), and polypentapeptide gas sterilized (29). Animals were anesthetized and a laparotomy was conducted to reveal the cranial portion of the ileum. The abdominal wall muscle peritoneum was excoriated until hemorrhage was noted. In sham animals, there was no physical barrier placed between bowel loop and the abdominal wall. In two of the study groups, the polypentapeptide sheet was placed directly over the excoriated area. The intestinal loop was then loosely secured to excoriated area with 2-O nylon (stay suture) which was tied subcutaneously in all groups. Four puncture wounds were made with a 20-gauge hypodermic needle in the bowel that was apposed to the excoriated peritoneal musculature which allowed leakage of intestinal contents and contamination. On Day 7 postsurgery, the animals were anesthetized and the stay suture was removed. On Day 14, all animals were sacrificed and adhesions were graded. The incidence of significant adhesions was 28% for the barrier group versus 90% for control animals (P < 0.05). The results of this study indicate that the polypentapeptide of elastin sheet is an effective physical barrier in this surgically induced contaminated wound model.

Animals↗
PubMed1993

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.

Amino Acid Sequence↗
PubMed1993

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.

Amino Acid Sequence↗
PubMed1992

Reduction-driven polypeptide folding by the delta Tt mechanism.

Poly(Gly-Val-Gly-Val-Pro), i.e., poly(GVGVP), exhibits composition and solute dependence of Tt, the temperature of the inverse temperature transition at which hydrophobic folding and assembly occur on raising the temperature. Importantly, a means whereby the value of Tt is lowered from above to below the working temperature becomes an isothermal means of driving folding and assembly, i.e., of achieving free energy transduction. Using poly[0.73(GVGVP),0.27(GK[NMeN]GVP)] where [NMeN] indicates N-methyl nicotinamide attached to the epsilon-NH2 of the Lys(K) residue, chemical and electrochemical reductions are found to remarkably lower the value of Tt; reduction can drive hydrophobic folding and assembly as effectively as decreasing ionization. Changing the redox state of a protein becomes yet another means of achieving free energy transduction by the delta Tt mechanism.

Amino Acid Sequence↗
PubMed1992

Hydrophobicity-induced pK shifts in elastin protein-based polymers.

Three polypentapeptides--poly[0.8(GVGVP), 0.2(GEGVP)], poly[0.8(GVGIP), 0.2(GEGIP)], and poly[0.75(GFGVP), 0.25(GEGVP)]--all analogues of the polypentapeptide of elastin--(Val1-Pro2-Gly3-Val4-Gly5)n or poly(VPGVG)--have been prepared to determine the effect of changing the hydrophobicity, i.e., Val1----Ile1 (I) and Val4----Phe4 (F), on the pKa and the temperature dependence of pKa of the Glu (E) residue. Shifts in pKa as large as 1.7 units are observed and the temperature dependence is much steeper for the structure-dependent proximity of the more hydrophobic Ile1 residues to the Glu4 residue. Even though this system is dominated by the inverse temperature transition of hydrophobically driven folding on raising the temperature, the effect of adding 0.15 N NaCl is to suppress the hydrophobicity-induced pKa shift.

Amino Acid Sequence↗
PubMed1992

Hydrophobicity scale for proteins based on inverse temperature transitions.

In general, proteins fold with hydrophobic residues buried, away from water. Reversible protein folding due to hydrophobic interactions results from inverse temperature transitions where folding occurs on raising the temperature. Because homoiothermic animals constitute an infinite heat reservoir, it is the transition temperature, Tt, not the endothermic heat of the transition, that determines the hydrophobically folded state of polypeptides at body temperature. Reported here is a new hydrophobicity scale based on the values of Tt for each amino acid residue as a guest in a natural repeating peptide sequence, the high polymers of which exhibit reversible inverse temperature transitions. Significantly, a number of ways have been demonstrated for changing Tt such that reversibly lowering Tt from above to below physiological temperature becomes a means of isothermally and reversibly driving hydrophobic folding. Accordingly, controlling Tt becomes a mechanism whereby proteins can be induced to carry out isothermal free energy transduction.

Amino Acid Sequence↗
PubMed1992

Hydrophobicity of amino acid residues: differential scanning calorimetry and synthesis of the aromatic analogues of the polypentapeptide of elastin.

Relative hydrophobicities of aromatic amino acid residues are investigated by using differential scanning calorimetry (DSC) on 10 synthetic copolypentapeptides of poly(VPGVG) of elastin. Utilizing the hydrophobic-driven process of the inverse temperature transition exhibited by these polypentapeptides in aqueous solution, the relative hydrophobicities of Phe, Trp, and Tyr residues are determined by the critical temperature and heat of the transition. The DSC data for the aromatic residue containing copolypentapeptide aqueous solution indicate that tryptophan is the most hydrophobic amino acid residue, phenylalanine the third most hydrophobic on basis of transition temperature and the second on basis of transition heat. For tyrosine, significant differences are observed between the phenolic and the phenoxide anionic states. At pH 7, where tyrosine is protonated, it is found to be the second most hydrophobic amino acid residue on the basis of the transition temperature, whereas on the basis of the heat of transition, it is less hydrophobic than both tryptophan and phenylalanine. Changing the pH from pH 7 to pH 12, for example, for poly[0.8(VPGVG), 0.2(VPGYG)] in aqueous solution shifts the transition temperature from 7 to 49 degrees C with a dramatically reduced heat. On the basis of both the transition temperature scale and the heat of transition, the hydroxylated tyrosine appears less hydrophobic than glycine.

Amino Acid Sequence↗
PubMed1992

Cell adhesion and growth on synthetic elastomeric matrices containing Arg-Gly-Asp-Ser-3.

Synthetic elastomeric polypeptide matrices based on the repeating amino acid sequences of elastin have biophysical and biological properties which are favorable for prosthetic materials. An important requirement envisaged for some applications is the ability to support cell adhesion and growth. The X20-poly-(GVGVP), the gamma-irradiation cross-linked elastomeric matrix based on the repeating pentamer Val-Pro-Gly-Val-Gly, and X20-poly[n(GVGVP), (GRGDSP)] containing the covalently incorporated cell adhesion sequence Arg-Gly-Asp-Ser (RGDS) were synthesized. These matrices were tested for their ability to support the adhesion and growth of bovine aortic endothelial cells and of bovine ligamentum nuchae fibroblasts. Adhesion experiments carried out in albumin-containing media showed that matrices containing 60:1, 40:1, and 20:1 ratios of (GVGVP):(GRGDSP) supported maximal cell attachment, that matrices containing 100:1 exhibited an intermediate level of attachment and that matrices composed of 500:1 and (GVGVP) alone were very poor supports for cell attachment. Serum in the media promoted submaximal cell attachment to X20-poly(GVGVP) but did not permit substantial cell growth. Cell growth was supported by matrices having high ratios of (GRGDSP). Ratios of 60:1, 40:1, and 20:1 supported three population doublings of endothelial cells over 3 days resulting in confluent matrix-adherent monolayers. Ratios of 40:1 and 20:1 similarly supported the growth of fibroblasts.

Amino Acid Sequence↗
PubMed1991

Phosphorylation and dephosphorylation modulation of an inverse temperature transition.

Poly[15(IPGVG),(RGYSLG)], where RGYSLG is a protein kinase site, was synthesized. On raising the temperature of a 5 mg/ml solution, this polypeptide undergoes an inverse temperature transition at 18 degrees C in which it folds into a contracted state by optimizing intramolecular hydrophobic interactions. Averaging the data of five experiments, phosphorylation by means of a 3':5' cyclic AMP dependent protein kinase to the extent of one phosphate in 360 residues raises the temperature of the folding transition to 32 degrees C. The shift is completely reversed on dephosphorylation by alkaline phosphatase. Phosphorylation is hereby shown to be the most potent chemical perturbation known for shifting the temperature of an inverse temperature transition, which has been shown to be an efficient mechanism for achieving chemomechanical transduction (mechanochemical coupling).

Alkaline Phosphatase↗
PubMed1991

Differential scanning calorimetry studies of NaCl effect on the inverse temperature transition of some elastin-based polytetra-, polypenta-, and polynonapeptides.

Differential scanning calorimetry studies of the effect of NaCl on protein-based polymer self-assembly has been carried out on six elastin-based synthetic sequential polypeptides--i.e., the polypentapeptide (L-Val1-L-Pro2-Gly3-L-Val4-Gly5)n and its more hydrophobic analogues (L-Leu1-L-Pro2-Gly3-L-Val4-Gly5)n and (L-Val1-L-Pro2-L-Ala3-L-Val4-Gly5)n; the polytetrapeptide (L-Val1-L-Pro2-Gly3-Gly4)n and its more hydrophobic analogue (L-Ile1-L-Pro2-Gly3-Gly4)n; and the polynonapeptide (a pentatetra hybrid), (L-Val1-L-Pro2-Gly3-L-Val4-Gly5-L-Val6-L-Pro7-Gly8-Gly9++ +)n. Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order of the polypentapeptide, as the temperature is raised from below to above that of the transition, has been repeatedly observed using different physical characterizations. In the present experiments, it is observed that the transition temperatures of the polypeptides studied are linearly dependent on NaCl concentration. The molar effectiveness of NaCl in shifting the transition temperature delta Tm/[N], is about 14 degrees C/[N], with the dependence on peptide hydrophobicity being fairly small. Interestingly, however, the delta delta Q/[N] does depend on the hydrophobicity of a polypeptide.

Amino Acid Sequence↗
PubMed1990

Differential scanning calorimetry studies of the inverse temperature transition of the polypentapeptide of elastin and its analogues.

Differential scanning calorimetry studies have been carried out on the sequential polypeptide of elastin, (L-Val1-L-Pro2-Gly3-L-Val4-Gly5)n, abbreviated as PPP, and its more hydrophobic analogues (L-Leu1-L-Pro2-Gly3-L-Val4-Gly5)n, referred to as Leu1-PPP, and (L-Ile1-L-Pro2-Gly3-L-Val4-Gly5)n, referred to as Ile1-PPP Consistent with inverse temperature transitions, the temperatures of the transitions for which maximum heat absorption occurs are inversely proportional to the hydrophobicities of the polypentapeptides (31 degrees C for PPP, 16 degrees C for Leu1-PPP, and 12 degrees C for Ile1-PPP), and the endothermic heats of the transitions are small and increase with increasing hydrophobicity, i.e., 1.2, 2.9, and 3.0 kcal/mol pentamer for PPP, Leu1-PPP, and Ile1-PPP, respectively. Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order, as the temperature is raised above that of the transition, has been repeatedly observed using different physical characterizations. Furthermore, the studies demonstrated identical conformations for PPP and Il21-PPP above and below the transition. Both heats and temperatures of the transitions vary with hydrophobicity, but not in simple proportionality.

Amino Acid Sequence↗
PubMed1990

Conformation of a cyclic decapeptide analog of a repeat pentapeptide sequence of elastin: cyclo-bis(valyl-prolyl-alanyl-valyl-glycyl).

The conformation of a cyclic decapeptide analog of a repeat sequence of elastin has been determined in the crystalline state using X-ray crystallographic techniques. Tetragonal crystals were grown from a solution of the decapeptide in water; space group P4(2)2(1)2, a = 19.439(2) & c = 13.602(1) A, with four formula units (C40H66N10O10.4H2O) per unit cell. The cyclic decapeptide in the crystal exhibits exact twofold symmetry. The asymmetric unit contains one pentapeptide and two water molecules for a total of 32 nonhydrogen atoms. The structure has been determined by the application of direct methods and refined by full-matrix least squares to an R index of 0.053 for 2272 reflections with intensities greater than 2 sigma(I). The backbone conformation of the asymmetric pentapeptide can be described as consisting of a double beta bend of Type III-I. The Type III turn has Pro (phi = -59.3 degrees, psi = -26.8 degrees) and Ala (phi = -65.9 degrees, psi = -23.1 degrees) at the corners while Type I turn has Ala (phi = -65.9 degrees, psi = -23.1 degrees) and Val (phi = -98.9 degrees, psi = 8.3 degrees) as the corner residues. The cyclic decapeptide has two such double bends linked together by Gly-Val bridges.

Amino Acid Sequence↗