Inverse temperature transitions assembly transition

The inverse temperature transition is a specific mechanism whereby thermal energy (heat) provides an increase in order of the protein part of the system. A decrease in entropy of this sort has been termed negative entropy by Schrodinger. ° While the total entropy (disorder) for the complete system of protein and water increases as the temperature is raised, the structural protein component, critical to the conversion of thermal energy to mechanical work, increases in negative entropy. The protein component increases in order by the folding that shortens length and by the assembly of oillike domains that builds structures. 

The Inverse Temperature Transition A Hydrophobic Folding and Assembly Transition... 

The protein-based polymer is soluble in water at temperatures below its coexistence line where the hydrophobic residues are surrounded by hydrophobic hydration. As the positive (-TAS) term due to hydrophobic hydration becomes larger than the negative AH term, simply due to increasing the value of T, solubility of a protein-based polymer is lost, and it hydrophobicaUy folds and assembles. The inverse temperature transition is a hydrophobic association transition. 

More oil-like R-groups in our model protein studies resulted in lower temperatures for the onset of the inverse temperature transition of hydrophobic folding and assembly (see section 5.3.2). We argued that more oil-like R-groups in... 

Remember that the difference between these polymers is quite modest. They differ by only one CH2 in each five residues. However, because they exhibit inverse temperature transitions at different onset temperatures, one polymer can be separated from the other and self-assembled into an ordered structure with a minimal input of energy. 

A.2.3 Fr ATPase Assembles on Raising the Temperature by Hydrophobic Association of an Inverse Temperature Transition... 

Because assembly of the Fi-ATPase is dominated by an inverse temperature transition of hydrophobic association, the structure disassembles on lowering the temperature, that is, it exhibits cold denatmation. 

Now, it has been shown for materials such as poly(propylene diol) (wherein both the absorption maximum for loss shear modulus and loss permittivity overlap near the frequency of IHz) that their normalized curves perfectly superimpose over their frequency band width. - As shown in Figure 9.15, the lower frequency loss shear modulus curves uniquely overlap with the loss permittivity data at higher frequency. As such the former is melded to calibrate the loss permittivity data to obtain a coarse estimate of the elastic modulus values. This provides an independent demonstration of the mechanic il resonance near 3 kHz and also allows reference to the 5 MHz dielectric relaxation as a mechanical resonance. Thus, as the folding and assembly of the elastic protein-based polymers proceed through the phase (inverse temperature) transition, the pentamers wrap up into a structurally repeating helical arrangement like that represented in Figure 9.17. 

Figure 1 A. Temperature versus normalized turbidity curves for a series of guest amino acid residues occurring at the frequency of 4 guest residues per 100 residues, i.e., fx = 0.2. The value of Tj, the temperature for the onset of the inverse temperature transition for hydrophobic folding and assembly, is defined as the temperature for 50% of maximal turbidity. Note that more hydrophobic guest residues lower the value of T,. and less hydrophobic, more polar residues raise the value of Ti.

The importance of ELRs resides in the fact that these polymers show a versatile and broad range of interesting properties above and beyond their simple mechanical performance that are not easily found together in other materials, including stimuli-responsive behavior or the ability to self-assemble. These properties arise due to a molecular transition of the polymer chain in the presence of water at temperatures above a certain level. This transition, known as the Inverse Temperature Transition (ITT) [7, 8], has become the key issue in the development of peptide-based polymers for use as molecular machines and materials. 

T[ and Tj, are the on-set temperature for the hydrophobic folding and assembly transition, that is, inverse temperature transition, in pbs (0.15 N NaCl, 0.01 M phosphate) as determined by light scattering and in water as determined by DSC, respectively. Both values are linearly extrapolated tofx = 1 and rounded to a number divisible by 5. AH and AS are the values at/x = 0.2 on the curve for a linear fit of the DSC derived endothermic heats and entropies of the transitions for die polymers in water. 

Elastin-like polypeptides are polymers that consist of alternating hydrophobic blocks and crosslinking domains. Such polymers can be produced recombinantly and are composed of the repeating amino acid sequence (Val-Pro-Gly-Xaa-Gly)m, where Xaa is a hydrophobic domain that facilitates both self-aggregation and elastomeric functions. Thus, they undergo an inverse phase transition, which can be used to promote temperature-dependent self-assembly [125]. 

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