Mechanochemical coupling in synthetic polypeptides by modulation of an inverse temperature transition.

Abstract

For the polypentapeptide of elastin, (L-Val-L-Pro-Gly-L-Val-Gly The polypeptide ofinterest is the polypentapeptide of elastin, (L-Val-L-Pro-Gly-L-Val-Gly)n, discovered in porcine elastin (1, 2). In bovine elastin, the longest sequence between lysine residues, which can form the cross-links, is 72 residues; for a continuous and unsubstituted sequence of 57 residues, this is the polypentapeptide (3). The synthetic polypentapeptide is soluble in water in all proportions below 250C, but when the temperature is raised above 250C, aggregation occurs, followed by settling and phase separation. At 40'C, the more dense viscoelastic phase is 38% peptide and 62% water by weight (4 In thermoelasticity studies when the synthetic elastomer is stretched and held at fixed length and the temperature is raised through the transition range from 20'C to 40'C, there is a dramatic increase in elastomeric force (5). Above 40TC, however, in a plot of In(elastomeric force/temperature) versus temperature the slope is nearly 0 (5); these data, along with composition studies that show a near constant coacervate volume and composition in the 40-60'C temperature range (4), provide one basis for indicating that the elastomeric force is dominantly entropic in origin. A most instructive demonstration that this transition, centered near 30'C, in which elastomeric force develops is an inverse temperature transition is given when the more hydrophobic polypentapeptide (L-Ile-L-Pro-Gly-L-Val-Gly),,-i.e., the [Ilel]polypentapeptide-is similarly cross-linked and studied (18). For this more hydrophobic elastomeric matrix, the temperature of the transition for development of elastomeric force in a thermoAbbreviations: 4%-Glu-PPP, elastin polypentapeptide in which 4% of the residues are glutamic acid; X2-, crosslinked at 20 Mrad y-irradiation. *With the exception of two reports from one other laboratory (6, 7), to our knowledge, the only synthesis and physical characterizations of the sequential polypeptides of elastin and their analogs are due to the work of, and collaborations involving, this laboratory. Because of this, an unseemly high proportion of the references in this article will necessarily be to our own publications. 3407The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

The molecular basis of the temperature‐ and pH‐induced conformational transitions in elastin‐based peptides

“…Urry and co-workers have observed that when the valine in position 4 of (VPGVG) n is replaced in 1 out of 5 pentamers by a glutamic acid residue, the transition temperature shifts from 25°C at both pH 2 and pH 7 to 25°C at pH 2 and 70°C at pH 7. 17 Moreover, this biopolymer also undergoes a pH-modulated contraction and relaxation with a change from higher to lower pH at 37°C. 17 Therefore, the glutamic acidsubstituted (VPGVG) 18 represents an interesting model system for the study of the contributions of polar and nonpolar side chains and their hydration to the conformational states of biopolymers.…”

Development of Rules for Folding of Biotechnology Produced Protein.

“…to the less polar COOH moieties). This is because the temperature of the transition is lowered as the polypeptide becomes more hydrophobic, and it is raised as the polypeptide becomes less hydrophobic (16). The molecular interpretation is that the pull of the C00r-moiety to achieve its waters of hydration destructures the waters of hydrophobic hydration, thereby removing the thermodynamic driving force for folding (18).…”

“…Simplicity of the Assay System and efficiency of the ATt Mechanism for Chemomechanical Transduction: For both thermomechanical transduction and chemomechanical transduction, the demonstration of forces developed and work performed can be by means of the simple assay of watching a strip of the cross-linked matrix pick up a weight when the energy source is thermal for thermomechanical transduction (thermally driven folding), or pick up a weight when the energy source is chemical, for example, as when the salt concentration is raised or when the concentration of proton is raised to achieve chemically driven folding (16,17). The forces are obviously real, and they are dramatic with an efficiency, for example, in the conversion of chemical energy into mechanical work that is more than an order of magnitude greater than previously demonstrated for the charge-charge repulsion mechanism of chemomechanical transduction (13).…”

“…Polymers IV and V were designed on the basis of the working 13-spiral structure of poly(GVGVP) shown schematically in Figure 5A (13,16). For the 13-spiral structure, the distance between turns is approximately one nanometer (30,31).…”

“…This mechanism can be used to drive chemomechanical transduction as the polypeptide folding into a 3spiral can be used to lift a weight in elastomeric bands obtained on y-irradiation of the coacervate state (13,16,17). This mechanism for driving folding and unfolding is an order of magnitude more efficient in the amount of chemical energy (due to an increase in proton concentration) required to lift a given weight than is the charge-charge repulsion mechanism using the same COOH/CO--chemical couple (13,21), and (ap/0f)a, where f is force, is negative for the new mechanism (13,35) and positive for the latter (21).…”