Protein-based machines hydrophobic/elastic

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. 

V in Table 5.5 with 0,2,3,4, and 5 F residues per 30-mer exhibits a systematic nonlinear increase in steepness, that is, in positive cooperativity, and an associated nonlinear increased pKa shift, as plotted in Figure 5.34. The energy required to convert from the COOH state to the COO" state systematically in a supralinear way becomes less and less, as more Phe residues replace Val residues. The energy required to convert from the hydrophobically dissociated state of COO" to the hydrophobically associated (contracted) state of COOH becomes less, as the model protein becomes more hydro-phobic. The elastic-contractile protein-based machine becomes more efficient as it becomes more hydrophobic. The cooperativity of Model Protein iv with a Hill coefficient of 2.6 is similar... 

On the Relevance of Hydrophobic and Elastic Consilient Mechanisms to Biology s Protein-based Machines... 

This chapter discusses key protein-based machines of biology to demonstrate the relevance of the hydrophobic and elastic consilient mechanisms. The objective in this chapter, therefore, is to investigate selected examples of biology s protein-based machines and to look at the molecular level for a coherence of phenomena with the designed elastic model... 

In general, then, the energy conversions of biology reduce to the production of ATP and the uses of ATP, that is, the production of ATP by the five protein-based machines of the inner mitochondrial membrane and the thousands of subsequent protein-based machines that do the necessary work of the cell. This constitutes yet an enormous task that will fill hundreds of volumes in the future of protein-based machines. The intention of this volume, however, is to add a simplifying feature of a common groundwork of explanation for each of the hydrophobic and elastic consilient mechanisms. For the function of protein-based machines of biology, this perspective recovers an attractive element of simplification. 

Even so, crystal structures provide the best snapshots of forces in action. Crystal structures provide an unparalleled opportunity to assess relevance to the major protein-based machines of biology of the free energy transduction so dominantly displayed by elastic-contractile model proteins (as developed in Chapter 5). If the apolar-polar repulsive free energy of hydration, AG.p, the operative component of the Gibbs free energy of hydrophobic association, AGha> is active in ATP synthase, then it should become apparent in these snapshots. 

Elastic forces come into play as hydrophobic associations stretch interconnecting chain segments. Only if the elastic deformation is ideal does all of the energy of deformation become recovered on relaxation. To the extent that hysteresis occurs in the elastic deformation/ relaxation, energy is lost and the protein-based machine loses efficiency. Thus, the elastic consilient mechanism, whereby the force-extension curve can be found to overlay the force-relaxation curve becomes the efficient mechanical coupler within the vital force. The objective now becomes one of understanding the age-old problem of a reluctance to discard past idols. 

The concept of two distinct but interlinked mechanical processes, expanded here as the coupling of hydrophobic and elastic consilient mechanisms, entered the public domain in the publication of Urry and Parker. Experimental results on elastic-contractile model proteins forged the concept, and the work of Urry and Parker extended the concept to contraction in biology. Unexpected in our examination of the relevance of this perspective to biology was to find the first clear demonstration of the concept in biology in a protein-based machine of the electron transport chain as a transmembrane protein of the inner mitochondrial membrane. Unimaginable was the occurrence of the coupled forces precisely at the nexus at which electron transfer couples to proton pumping. 

ATPase (the Fi-motor of ATP synthase) demonstrate a dominant role of the hydrophobic and elastic consilient mechanisms in the function of this pivotal protein-based machine of biology. 

We have discussed the nexus of hydrophobic and elastic consilient mechanisms in Complex III at the intersection of electron flow and proton translocation (electro-chemical transduction) that was unimaginable, absent the detailed analysis of structure. The hydrophobic and elastic consilient mechanisms, however, when applied to the general structure and phenomenology of the Fi-motor of ATP synthase (chemo-chemical transduction), gave rise to a host of successful predictions, and, when applied to the structure and phenomenology of the myosin II motor (chemo-mechanical transduction), resulted in a half-dozen realized expectations. These findings do much to substantiate the relevance of the hydrophobic and elastic consilient mechanisms to the protein-based machines of biology. 

The above three discussed protein-based machines—Complex III of the electron transport chain, ATP synthase/Fj-ATPase, and the myosin II motor of muscle contraction—represent the three major classes of energy conversion that sustain Life. Therefore, the facility with which the consilient mechanisms explain their function indeed support the thesis that biology s vital force arises from the coupled hydrophobic and elastic consilient mechanisms. 

Thus, from the perspective of the inverse temperature transition, evolution and natural selection become apparent consequences for protein-based machines that function by the hydrophobic and elastic consilient mechanisms. 

As shown in the hexagonal array in Figure 5.22, five different energy inputs can perform mechanical work by the consilient mechanism. The set of elastic-contractile model proteins capable of direct utilization of hydrophobic association for contraction are called protein-based molecular machines of the first kind. These are enumerated below with brief consideration of the reversibility of these machines. 

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