Inverse temperature transition property

Convenient purification of microbially produced transductional protein-based polymers, e.g. poly(GVG T), from the cell lysate is based on a methodologv w hich utilizes the fundamental inverse temperature transitional properties (Urry et al., 1995b McPherson et al, 1996). First the bacterial cells are separated from the growth medium either by centrifugation or filtration and resuspened in Tris-HCl buffer, 50 mM, pH 8.0. Then the cells are lysed by ultrasonic disruption or French press to release the cell contents. The cell lysate is cooled to 4 C and centrifuged at high speed (10,000 x g) to remove the cold insoluble materials. The supernatant... 

Some polymers have been purified on the basis of their physicochemical properties. For example, silk-like polymers have been purified by taking advantage of their low solubility in aqueous medium (13). Elastin-like polymers (ELPs) have been purified by temperature cycling above and below their inverse temperature transition (Tt) (14). This technique has been extended to produce an ELP-tag that can be used to purify a number of recombinant proteins by temperature cycling, which may be faster and less expensive than affinity chromatography (15). 

Table 1. Hydrophobicity scale for protein-based polymers and proteins based on the properties of the inverse temperature transition of elastic protein-based polymers, poly[/v(GVGVP), (GXGVP)]. ...

Interestingly, this mechanical performance is accompanied by an extraordinary biocompatibiUty, although, however, the most striking properties are perhaps their acute smart and self-assembhng nature. These properties are based on a molecular transition of the polymer chain in the presence of water when their temperature is increased above a certain level. This transition, called the inverse temperature transition (ITT), has become the key issue in the development of new peptide-based polymers as molecular machines and materials. The understanding of the macroscopic properties of these materials in terms of the molecular processes taking place around the ITT has established a basis for their functional and rational design [102]. 

The essential aspect of the capacity of the inverse temperature transition to achieve diverse energy conversions resides within large chain molecules, which were just becoming known when the first edition of Schrodinger s book appeared. As we have sketched above, the functional properties of the model protein-... 

Due to the struggle to survive under circumstances of limited food supply, organisms evolve to use the most efficient mechanism available to their composition. The most efficient mechanism available to the proteins that sustain Life would seem to be the apolar-polar repulsive free energy of hydration as observed for the inverse temperature transitions for hydrophobic association. The efficiency of designed elastic-contractile protein-based machines and a number of additional properties make designed protein-based materials of substantial promise for the marketplace of the future. 

A vital property of these model proteins is that they are more ordered above the transition temperature defined by the binodal or coexistence line in Figure 5.3. The polymer component of this water-polypeptide system becomes more ordered or structured on increased temperature from below to above the transition. This behavior is the inverse of that observed for most systems, as discussed above. In particular, we developed the term inverse temperature transition when the precursor protein and chemical fragmentation products of the mammalian elastic fiber changed from a dissolved state, and therefore when molecules were randomly dispersed in solution, to a state of parallel-aligned twisted filaments as the temperature was raised from below to above the phase transition. - ... 

T, to a new value of T, caused by an energy input represented by % to provide a measure of the change in Gibbs free energy for hydrophobic association of the protein-based polymer. Therefore, Tt, the onset temperature for the inverse temperature transition, represents an intrinsic property of the hydrophobic consilient mechanism of energy conversion. 

By considering the T,-based hydrophobicity scale noted in Chapter 2 and developed in Chapter 5 (see Table 5.1), the primary family is readily recognized it is valine (Val, V), methionine (Met, M), isoleucine (He, I), leucine (Leu, L), and phenylalanine (Phe, F). These are all hydrophobic residues without any other functional capacity. The residues valine and methionine exhibit a similar degree of oil-like character. Substitution of one by the other would hardly change the temperature of the inverse temperature transition at all. Conversion from Val to He or Leu results in the simple addition of a CH2 group, which constitutes a modest increase in oil-like character. Conversion of Val to Phe does involve a substantied increase in oil-like character, but adds no other physical property, only an increase in oil-like character. 

As reviewed in Chapter 7 with a focus on the issue of insolubility, extensive phenomenological correlations exist between muscle contraction and contraction by model proteins capable of inverse temperature transitions of hydrophobic association. As we proceed to examination of muscle contraction at the molecular level, a brief restatement of those correlations follows with observations of rigor at the gross anatomical level and with related physiological phenomena at the myofibril level. Each of the phenomena, seen in the elastic-contractile model proteins as an integral part of the comprehensive hydrophobic effect, reappear in the properties and behavior of muscle. More complete descriptions with references are given in Chapter 7, sections 7.2.2, and 7.2.3. 

The responsive behavior of ELRs has been defined as their ability to respond to external stimuli. This property is based on a molecular transition of the polymer chain in the presence of water at a temperature above a certain level, known as the Inverse Temperature Transition (ITT). This transition, whieh shares most of the properties of the lower critical solution temperature (LCST), although it also differs in some respects, particularly as regards the ordered state of the folded state, is clearly relevant for the application of new peptide-based polymers as molecular devices and biomaterials. Below a specific transition temperature (T,), the free polymer chains remain as disordered, random coils [20] that are fully hydrated in aqueous solution, mainly by hydrophobic hydration. This hydration is characterized by ordered, clathrate-like water structures somewhat similar to those described for crystalline gas hydrates [21, 22], although somewhat more heterogeneous and of varying perfection and stability [23], surrounding the apolar... 

In contrast to the amines, inversion of configuration for phosphines is generally negligibly slow at ambient temperature. This property has made it possible for chiral phosphines to be highly useful as ligands in transition metal-catalyzed asymmetric syntheses. 

FIGURE 28, Modified Arrhenius plot of Jin In against Inverse temperature for thermally oxidized poly-(butadlene). The glass-transition temperature Is clearly visible, plus a transition attributed to an Intramolecular property of the probe [after figure in Eur. Polym. J., 13., 825 (1977)]. 

---